1.
An identifier in java must begin with a letter , a
dollar sign($), or an underscore
(-);
subsequent characters may be letters, dollar signs, underscores, or digits.
2.
There are three top-level elements that may appear
in a file. None of these elements is required. If they are present, then they
must appear in the following order:
-package declaration
-import statements
-class definitions
-package declaration
-import statements
-class definitions
3.
A static method can't be overridden to non-static
and vice versa.
4.
The variables in java can have the same name as
method or class.
5.
All the static variables are initialized when the
class is loaded.
6.
An interface can extend more than one interface,
while a class can extend only one class.
7.
The variables in an interface are implicitly final
and static.If the interface , itself, is declared as public the methods and
variables are implicitly public.
8.
A final class cannot have abstract methods.
9.
All methods of a final class are automatically
final.
10.
While casting one class to another subclass to
superclass is allowed without any type casting.
e.g.. A extends B , B b = new A(); is valid but not the reverse.
e.g.. A extends B , B b = new A(); is valid but not the reverse.
11.
The String class in java is immutable. Once an
instance is created, the string it contains cannot be changed.
e.g. String s1 = new String("test"); s1.concat("test1"); Even after calling concat() method on s1, the value of s1 will remain to be "test". What actually happens is a new instance is created.
But the StringBuffer class is mutable.
e.g. String s1 = new String("test"); s1.concat("test1"); Even after calling concat() method on s1, the value of s1 will remain to be "test". What actually happens is a new instance is created.
But the StringBuffer class is mutable.
12.
The short circuit logical operators && and
|| provide logical AND and OR operations on boolean types and unlike & and
| , these are not applicable to integral types. The valuable additional feature
provided by these operators is the right operand is not evaluated if the result
of the operation can be determined after evaluating only the left operand.
13.
The difference between x = ++y; and x = y++;
In the first case y will be incremented first and then assigned to x. In second case first y will be assigned to x then it will be incremented.
In the first case y will be incremented first and then assigned to x. In second case first y will be assigned to x then it will be incremented.
14.
The initialization values for different data types
in java is as follows
byte = 0, int = 0, short = 0, char = '\u0000', long = 0L, float = 0.0f, double = 0.0d, boolean = false,
object referenece(of any object) = null.
byte = 0, int = 0, short = 0, char = '\u0000', long = 0L, float = 0.0f, double = 0.0d, boolean = false,
object referenece(of any object) = null.
15.
An overriding method may not throw a checked
exception unless the overridden method also throws that exception or a
superclass of that exception.
16.
Interface methods can't be native, static,
synchronized, final, private, protected or abstract.
17.
The String class is a final class, it can't be
subclassed.
18.
The Math class has a private constructor, it can't
be instantiated.
19.
The two kinds of exceptions in java are : Compile
time (Checked ) and Run time (Unchecked) exceptions. All subclasses of
Exception except the RunTimeException and its subclasses are checked
exceptions.
Examples of Checked exception : IOException, ClassNotFoundException.
Examples of Runtime exception :ArrayIndexOutOfBoundsException,NullPointerException, ClassCastException, ArithmeticException, NumberFormatException.
Examples of Checked exception : IOException, ClassNotFoundException.
Examples of Runtime exception :ArrayIndexOutOfBoundsException,NullPointerException, ClassCastException, ArithmeticException, NumberFormatException.
20.
The various methods of Java.lang.Object are
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString and wait.
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString and wait.
21.
Garbage collection in java cannot be forced. The
methods used to call garbage collection thread are System.gc() and Runtime.gc()
22.
Inner class may be private, protected, final,
abstract or static.
23.
To refer to a field or method in the outer class
instance from within the inner class, use Outer.this.fieldname .
24.
Inner classes may not declare static initializers or
static members unless they are compile time constants i.e. static final var =
value;
25.
A nested class cannot have the same name as any of
its enclosing classes.
26.
An example of creation of instance of an inner class
from some other class:
class Outer
{
public class Inner{}
}
class Another
{
public void amethod()
{
Outer.Inner i = new Outer().new Inner();
}
}
class Outer
{
public class Inner{}
}
class Another
{
public void amethod()
{
Outer.Inner i = new Outer().new Inner();
}
}
27.
The range of Thread priority in java is 1-10. The
minimum priority is 1 and the maximum is 10. The default priority of any thread
in java is 5.
28.
Using the synchronized keyword in the method
declaration, requires a thread obtain the lock for this object before it can
execute the method.
29.
A synchronized method can be overridden to be not
synchronized and vice versa.
30.
There are two ways to mark code as synchronized:
a.) Synchronize an entire method by putting the synchronized modifier in the method's declaration.
b.) Synchronize a subset of a method by surrounding the desired lines of code with curly brackets ({}).
a.) Synchronize an entire method by putting the synchronized modifier in the method's declaration.
b.) Synchronize a subset of a method by surrounding the desired lines of code with curly brackets ({}).
31.
The notify() mthod moves one thread, that is waiting
on this object's monitor, into the Ready state. This could be any of the
waiting threads.
32.
The notifyAll() method moves all threads, waiting on
this object's monitor into the Ready state.
33.
The argument to switch can be either byte, short ,
char or int.
34.
Breaking to a label (using break <labelname>;)
means that the loop at the label will be terminated and any outer loop will
keep iterating. While a continue to a label (using continue <lablename>;)
continues execution with the next iteration of the labeled loop.
35.
To ensure that assertions don't become performance
liability, you can disable them when your program is started. Also by default,
assertions are disabled.
36.
An assertion is a statement in the Java language
that enables you to test your assumptions about your program.
37.
Some of the advantages of writing assertions while
programming are:
a.) Detect and correct bugs
b.) Enhance maintainability as writing assertions helps you document the inner workings of your code
a.) Detect and correct bugs
b.) Enhance maintainability as writing assertions helps you document the inner workings of your code
38.
In order for the javac compiler to accept code
containing assertions, you must use the -source 1.4 command-line option as in
the below example:
javac -source 1.4
TestClass.java
39.
The setClassAssertionStatus returns a boolean
instead of throwing an exception if it is invoked when it's too late to set the
assertion status (i.e., if the named class has already been initialized)
40.
A static method can only call static variables or
other static methods, without using the instance of the class. e.g. main()
method can't directly access any non static method or variable, but using the
instance of the class it can.
41.
The if() statement in java takes only boolean as an
argument. Please note that if (a=true){}, provided a is of type boolean is a
valid statement and the code inside the if block will be executed.
42.
The (-0.0 == 0.0) will return true, while
(5.0==-5.0) will return false.
43.
An abstract class may not have even a single
abstract method but if a class has an abstract method it has to be declared as
abstract.
44.
The valueOf() method converts data from its internal
format into a human-readable form. It is a static method that is overloaded
within String class for all of Java's built-in types, so that each type can be
converted properly into a string.
45.
The main difference between Vector and ArrayList is
that Vector is synchronized while the ArrayList is not.
46.
The statement float f = 5.0; will give compilation
error as default type for floating values is double and double can't be
directly assigned to float without casting.
47.
The equals() method in String class compares the
values of two Strings while == compares the memory address of the objects being
compared.
e.g. String s = new String("test"); String s1 = new String("test");
s.equals(s1) will return true while s==s1 will return false.
e.g. String s = new String("test"); String s1 = new String("test");
s.equals(s1) will return true while s==s1 will return false.
48.
The example of array declaration along with
initialization - int k[] = new int[]{1,2,3,4,9};
49.
The octal number in java is preceded by 0 while the
hexadecimal by 0x (x may be in small case or upper case)
e.g. octal :022 hexadecimal :0x12
e.g. octal :022 hexadecimal :0x12
50.
A constructor cannot be native, abstract, static,
synchronized or final.
- What is
meant by Java ?
- What is
meant by a class ?
- What is
meant by a method ?
- What are the
OOPS concepts in Java ?
- What is
meant by encapsulation ? Explain with an example
- What is
meant by inheritance ? Explain with an example
- What is
meant by polymorphism ? Explain with an example
- Is multiple
inheritance allowed in Java ? Why ?
- What is
meant by Java interpreter ?
- What is
meant by JVM ?
- What is a
compilation unit ?
- What is
meant by identifiers ?
- What are the
different types of modifiers ?
- What are the
access modifiers in Java ?
- What are the
primitive data types in Java ?
- What is
meant by a wrapper class ?
- What is
meant by static variable and static method ?
- What is
meant by Garbage collection ?
- What is
meant by abstract class
- What is
meant by final class, methods and variables ?
- What is
meant by interface ?
- What is
meant by a resource leak ?
- What is the
difference between interface and abstract class ?
- What is the
difference between public private, protected and static
- What is
meant by method overloading ?
- What is
meant by method overriding ?
- What is
singleton class ?
- What is the
difference between an array and a vector ?
- What is
meant by constructor ?
- What is
meant by casting ?
- What is the
difference between final, finally and finalize ?
- What is
meant by packages ?
- What are all
the packages ?
- Name 2
calsses you have used ?
- Name 2
classes that can store arbitrary number of objects ?
- What is the
difference between java.applet.* and java.applet.Applet ?
- What is a
default package ?
- What is
meant by a super class and how can you call a super class ?
- What is
anonymous class ?
- Name
interfaces without a method ?
- What is the
use of an interface ?
- What is a
serializable interface ?
- How to
prevent field from serialization ?
- What is
meant by exception ?
- How can you
avoid the runtime exception ?
- What is the
difference between throw and throws ?
- What is the
use of finally ?
- Can multiple
catch statements be used in exceptions ?
- Is it
possible to write a try within a try statement ?
50.What is the method to
find if the object exited or not ?
51.What is meant by a Thread
?
52.What is meant by
multi-threading ?
52.What is the 2 way of
creating a thread ? Which is the best way and why ?
53.What is the method to
find if a thread is active or not ?
54.What are the
thread-to-thread communcation ?
55.What is the difference
between sleep and suspend ?
56.Can thread become a
member of another thread ?
57.What is meant by deadlock
?
58.How can you avoid a
deadlock ?
59.What are the three typs
of priority ?
59.What is the use of
synchronizations ?
60.Garbage collector thread
belongs to which priority ?
61.What is meant by
time-slicing ?
62.What is the use of ‘this’
?
63.How can you find the
length and capacity of a string buffer ?
64.How to compare two
strings ?
65.What are the interfaces
defined by Java.lang ?
66.What is the purpose of
run-time class and system class
67.What is meant by Stream
and Types ?
68.What is the method used
to clear the buffer ?
69.What is meant by Stream
Tokenizer ?
70.What is serialization and
de-serialisation ? What is meant by Applet ?
71.How to find the host from
which the Applet has originated ?
72.What is the life cycle of
an Applet ?
73.How do you load an HTML
page from an Applet ?
74.What is meant by Applet
Stub Interface ?
75.What is meant by
getCodeBase and getDocumentBase method ?
76.How can you call an
applet from a HTML file ?
77.What is meant by Applet
Flickering ?
78.What are the different
types of Layouts ?
What is meant by CardLayout
?
What is the difference
between GridLayout and GridBagLayout
What is the difference
between menuitem and checkboxmenu item.
What is meant by vector
class,dictionary class,hash table,and property class ?
Which class has no duplicate
elements ?
What is resource bundle ?
What is an enumeration class
?
What is meant by Swing ?
What is the difference
between AWT and Swing ?
What is the difference
between an applet and a Japplet
What are all the components
used in Swing ?
What is meant by tab pans ?
What is the use of JTree ?
How can you add and remove
nodes in Jtree.
What is the method to expand
and collapse nodes in a Jtree ?
What is the use of JTable ?
What is meant by JFC ?
What is the class in Swing
to change the appearance of the Frame in Runtime.
How to reduce flicking in
animation ?
What is JDBC ?
How do you connect to the
database ? What are the steps ?
What are the drivers
available in JDBC ? Explain
How can you load the driver
?
What are the different types
of statement s ?
How can you created JDBC
statements ?
How will you perform
transactions using JDBC ?
What are the two drivers for
web apllication?
What are the different types
of 2 tier and 3 tier architecture ?
How can you retrieve warning
in JDBC ?
What is the exception thrown
by JDBC ?
What is meants by
PreparedStatement ?
What is difference between
PreparedStatement and Statement ?
How can you call the stored
procedures ?
What is meant by a ResultSet
?
What is the difference
between ExecuteUpdate and ExecuteQuery ?
How do you know which driver
is connected to a database ?
What is DSN and System DSN
and differentiate these two ?
What is meant by TCP, IP,
UDP ?
What is the difference
between TCP and UDP ?
What is a proxy server ?
What is meant by URL
What is the use of parameter
tag ?
What is audio clip Interface
and what are all the methods in it ?
What is the difference
between getAppletInfo and getParameterInfo ?
How to communicate between
applet and an applet ?
What is meant by event
handling ?
1.
What are all the listeners in java and explain ?
2.
What is meant by an adapter class ?
3.
What are the types of mouse event listeners ?
4.
What are the types of methods in mouse listeners ?
5.
What is the
difference between panel and frame ?
6.
What is the
default layout of the panel and frame ?
7.
What is meant
by controls and types ?
8.
What is the
difference between a scroll bar and a scroll panel.
9.
What is the
difference between list and choice ?
10.
How to place
a component on Windows ?
11.
What is a socket and server sockets ?
12.
When MalformedURLException and UnknownHost Exception
throws ?
13.
What is InetAddress ?
14.
What is datagram and datagram packets and datagram
sockets ?
15.
Write the range of multicast socket IP address ?
16.
What is meant by a servlet ?
17.
What are the types of servlets ? Explain
18.
What is the different between a Servlet and a CGI.
19.
What is the difference between 2 types of Servlets ?
20.
What is the type of method for sending request from
HTTP server ?
21.
What are the exceptions thrown by Servlets ? Why ?
22.
What is the life cycle of a servlet ?
23.
What is meant by cookies ?
24.
What is HTTP Session ?
25.
What is the difference between GET and POST methods
?
26.
How can you run a Servlet Program ?
27.
How to commuincate between an applet and a servlet ?
28.
What is a Servlet-to-Servlet communcation ?
29.
What is Session Tracking ?
30.
What are the security issues in Servlets ?
31.
What is HTTP Tunneling ?
32.
How do you load an image in a Servlet ?
33.
What is Servlet Chaining ?
34.
What is URL Rewriting ?
35.
What is context switching ?
36.
What is meant by RMI ?
37.
Explain RMI Architecture ?
38.
What is meant by a stub ?
39.
What is meant by a skelotn ?
40.
What is meant by serialisation and deserialisation ?
41.
What is meant by RRL ?
42.
What is the use of TL ?
43.
What is RMI Registry ?
44.
What is rmic ?
45.
How will you pass parameter in RMI ?
46.
What exceptions are thrown by RMI ?
47.
What are the steps involved in RMI ?
48.
What is meant by bind(), rebind(), unbind() and
lookup() methods
49.
What are the advanatages of RMI ?
50.
What is JNI ?
51.
What is Remote Interface ?
52.
What class is used to create Server side object ?
53.
What class is used to bind the server object with
RMI Registry ?
54.
What is the use of getWriter method ?
55.
What is meant by Javabeans ?
56.
What is JAR file ?
57.
What is meant by manifest files ?
58.
What is Introspection ?
59.
What are the steps involved to create a bean ?
60.
Say any two properties in Beans ?
61.
What is persistence ?
62.
What is the use of beaninfo ?
63.
What are the interfaces you used in Beans ?
64.
What are the classes you used in Beans ?
1. What are the
difference between Java and C++?
C++ does not have Garbage collector where as Java have Garbage
collector & Hence Memory management is easy in Java.Java is Platform
independent & hence it is portable among different platforms.There is no
multiple inheritance in Java & it can be implemented with interfaces.
2. What is Method
Signature?
The combination of method name and parameter list is called the method
signature.
3. What are Packages?
Packages are libraries of related classes and interfaces that are
grouped together.
4. What is an Abstract
class?
Abstract classes are classes from which no object can be initiated. Abstract
classes cannot have objects of their own. Abstract class can be subclassed
which in turn can instantiate and have objects of their own.
5. What are Interfaces?
Interfaces contain a collection of methods that are implemented
elsewhere. Methods in an interface class are public and abstract. Therefore
interface cannot be instantiated. · Provide security for application · An
interface can extend any number of interfaces · A class can implement any
number of interfaces · An interface can be implemented in a class by using the
keyword implements · Most often interfaces are used to bring about a
relationship between different classes.
6. What is an
Encapsulation?
Encapsulation is the mechanism that binds together code and the data it
manipulates and keeps both safe from outside interface and misuse.
7. What is inheritance?
It is the process by which one object acquires the properties of other
objects.
8. What is polymorphism?
The capability of the method to react differently on different objects
is called polymorphism.
9. What are constructors?
A constructor instantiates an object immediately upon creation. It has
the same name as the class in which it resides. And it is syntactically similar
to a method.
10. What is the
difference between Methods and constructors?
· Constructor has the same name as class in which it resides, where as
methods can have any name. · Constructor will be executed at the time of object
instantiation, where as method executes when ever it is called. · Constructor
will not have any return type. But methods may have return type. If method
doesn't have any return type, we have to declare that as 'void'.
11. What is garbage
collection in Java?
When no reference to an object exists, that object assumed to be no
longer needed, and the memory occupied by the object can be reclaimed. Garbage
collection only occurs sporadically during the execution of the program.
12. What is the use of
Finalize Method?
Sometimes an object will need to perform some action when it destroyed.
For example, if an object is holding some non-Java resources such as a file
handle or then you might want to make sure these resources are freed before an
object destroy. To handle such situations, Java provides a mechanism called
finalization. By using finalization we can define specific actions that will
occur when an object is just about to reclaim by the garbage collector.
13. What for transient
keyword is used?
Transient keyword is used for security purpose and when we use this
keyword for any object that particular object cannot be serializable.
14. What is the
difference between overloading of methods and overriding of methods?
When we use multiple methods with same name but with different
parameters we call it as Overloading of methods (these multiple methods has to
be created prior to their usage). And if we just use a predefined method and
write our own method then that is called as overriding of methods.
15. What is the
difference between String and StringBuffer?
String objects are said to be immutable, which means that they cannot
be changed. To change the string referenced by string variable we have to throw
away the reference to the old string & replace it with a reference to a new
one. But StringBuffer object can be altered directly and they are called
mutable Strings.
16. Define instanceof
operator and equals() method?
The instanceof operator returns true or false based on whether the
object is an instance of the named class or any of that class's subclasses. It
is possible to have two different String objects that contain the same values.
If we use == operator to compare these objects, they are considered to be
unequal. Although their contents match, they are not the same objects. In order
to see whether two String objects have the same values, a method called
equals() is used.
17. What is an inner
class?
If we define a class inside a class, then that is called an inner
class. These inner classes can have access to variables and methods within the
scope of a top-level class that they would not have as a separate class. Rules
governing the scope of an inner class closely match those governing the
variables. An inner class's name is not visible outside its scope, except in a
fully qualified name, which helps in structuring classes within a package.
18. What is meant by
synchronized method?
When different threads act upon one common object a problem arises. A
thread could be Interrupted when it is attempting to modify an object, and then
another thread actually modifies that particular object. Consequently the first
thread is made to run again, and this time the object is modified once more,
which leads to errors. These type of problems can be avoided by using synchronized
method. With this method, one thread can finish execution before another thread
as per the priority can act upon the same object.
19. What are the
different types of initiating a thread?
There are two ways to initiate a thread, they are 1. Create a class
that extends the Thread class or 2. Create a class that implements the Runnable
interface.
20. What is meant by
serializable interface?
An object indicates that it can be used with streams by implementing
the Serializable interface. The sole purpose of Serializable interface is to
indicate that objects of that class can be stored and retrieved in serial form.
Serialization enables object persistence because the stored object continues to
serve a purpose even when no Java program is running. It contains information
that can be restored in a program so that it can resume functioning.
21. What does
try…catch…finally block will do?
The function of try … catch … finally block is "try this bit of
code that might cause an exception. If it executes okay, go on with the
program. If it doesn't, catch the exception deal with it and also execute the
code in finally clause either code in the try … catch block cause an exception
or not."
22. What is difference
between throw and throws?
If you write method that might throw an exception, then you must
declare the possibility, using throws statement. And if you don't handle the
exception in some way the method has no way to complete successfully. For this
situation we use throw statement. i.e. we throw an exception with a statement
that consists of keyword throw, followed by an exception object. This means we
can throw our own exception. For this we have to use try … catch block. Or we
can also create an exception object and throw it in single statement. For
example throw new DreadfulProblemException("Terrible difficulties")
23. What are the
differences between an interface and an abstract class?
Some use a semantic distinction: an abstract superclass models the
"is" relationship, while an interface models the "has"
relationship. The rule would thus be, if it's a subtype, inherit; otherwise,
implement. But where the object boundaries are themselves at stake, it's
circular to state this unless there are real-world metaphors to distinguish the
objects from their properties and parents. So where there are no real-world
metaphors, you have to understand the practical differences in Java (esp. vs.
C++). Most differences between interfaces and abstract classes stem from three
characteristics: · Both define method signatures that a derived class will
have. · An abstract class can also define a partial implementation. · A class
can implement many interfaces, but inherit from only one class.
24. What is the
difference between Swing and AWT?
1. Swing let you specify which look and feel your progra's GUI uses.
AWT components always have the look and feel of the native platform.
2. Swing components are implemented with absolute with no native code.
3. Swing components are in javax.swing package where as AWT components are in java.awt package.
2. Swing components are implemented with absolute with no native code.
3. Swing components are in javax.swing package where as AWT components are in java.awt package.
25. what is the
difference among Arrays, Vectors and Hash maps?
|
Arrays
|
Vectors
|
Hash Maps
|
|
|
|
Strings
Q - Java provides two different string classes from which string
objects can be instantiated. What
are they?
A - The two classes are:
String
StringBuffer
Q - The StringBuffer class is used for strings that are not allowed to
change. The String class is
used for strings that are modified by the program: True or False. If
false, explain why.
A - False. This statement is backwards. The String class is used for
strings that are not allowed to change. The
StringBuffer class is used for strings that are modified by the
program.
Q - While the contents of a String object cannot be modified, a
reference to a String object can be
caused to point to a different String object: True or False. If false,
explain why.
A - True.
Q - The use of the new operator is required for instantiation of
objects of type String: True or
False? If false, explain your answer.
A - False. A String object can be instantiated using either of the
following statements:
String str1 = new
String("String named str2");
String str2 = "String
named str1";
Q - The use of the new operator is required for instantiation of
objects of type StringBuffer: True
or False? If false, explain your answer.
A - True.
Q - Provide a code fragment that illustrates how to instantiate an
empty StringBuffer object of a
default length and then use a version of the append() method to put
some data into the object.
A - See code fragment below:
StringBuffer str5 = new
StringBuffer();//accept default initial length
str5.append("StringBuffer named str5");//modify length as
needed
Q - Without specifying any explicit numeric values, provide a code
fragment that will instantiate an
empty StringBuffer object of the correct initial length to contain the
string "StringBuffer named str6"
and then store that string in the object.
A - See the following code fragment:
StringBuffer str6 = new
StringBuffer("StringBuffer named str6".length());
str6.append("StringBuffer named
str6");
Q - Provide a code fragment consisting of a single statement showing
how to use the Integer wrapper class to convert a string containing digits to
an integer and store it in a variable of type int.
A - See code fragment below
int num = new
Integer("3625").intValue();
Q - Explain the difference between the capacity() method and the
length() methods of the StringBuffer class.
A - The capacity() method returns the amount of space currently allocated
for the StringBuffer object. The
length() method returns the amount of space used.
Q - The following is a valid code fragment: True or False? If false,
explain why.
StringBuffer str6 = new
StringBuffer("StringBuffer named str6".length());
A - True.
Q - Which of the following code fragments is the most efficient, first
or second?
String str1 = "THIS STRING
IS NAMED str1";
String str1 = new
String("THIS STRING IS NAMED str1");
A - The first code fragment is the most efficient.
System
Java provides the System class which provides a platform-dependent
interface between your program and various system resources: True or False? If
false, explain why.
A - False. Java provides the System class which provides a
platform-independent interface between your program and those resources.
Q - You must instantiate an object of the System class in order to use
it: True or False? If false, explain why.
A - False. You don't need to instantiate an object of the System class
to use it, because all of its variables and methods are class variables and
methods.
Q - The following code fragment can be used to instantiate an object of
the System class: True or False? If false, explain why.
System mySystemObject = new
System();
A - False. You cannot instantiate an object of the System class. It is
a final class, and all of its constructors are private.
Q - What is the purpose of the write() method of the PrintStream class?
A - The write() method is used to write bytes to the stream. You can
use write() to write data which is not intended to be interpreted as text (such
as bit-mapped graphics data).
Exceptions
Q - The exception-handling capability of Java makes it possible for you
to monitor for exceptional conditions within your program, and to transfer
control to special exception-handling code which you design. List five keywords
that are used for this purpose.
A - try, throw, catch, finally, and throws
Q - All exceptions in Java are thrown by code that you write: True or
False? If false, explain why.
A - False. There are situations where an exceptional condition
automatically transfers control to special exception-handling code which you
write (cases where you don't provide the code to throw the exception object).
Q - When an exceptional condition causes an exception to be thrown,
that exception is an object derived, either directly, or indirectly from the
class Exception: True or False? If false, explain why.
A - False. When an exceptional condition causes an exception to
be thrown, that exception is an object derived, either directly, or indirectly
from the class Throwable.
Q - All exceptions other than those in the RuntimeException class must
be either caught, or declared in a throws clause of any method that can throw
them: True or False? If false, explain why.
A - True.
Q - What method of which class would you use to extract the message
from an exception object?
A - The getMessage() method of the Throwable class.
Q - Normally, those exception handlers designed to handle exceptions
closest to the root of the exception class hierarchy should be placed first in
the list of exception handlers: True or False? If false, explain why.
A - False. The above statement has it backwards. Those handlers
designed to handle exceptions furthermost from the root of the hierarchy tree
should be placed first in the list of exception handlers.
Q - Explain why you should place exception handlers furthermost from
the root of the exception hierarchy tree first in the list of exception
handlers.
A - An exception hander designed to handle a specialized
"leaf" object may be preempted by another handler whose exception
object type is closer to the root of the exception hierarchy tree if the second
exception handler appears earlier in the list of exception handlers.
Q - In addition to writing handlers for very specialized exception
objects, the Java language allows you to write general exception handlers that
handle multiple types of exceptions: True or False? If false, explain why.
A - True.
Q - Your exception handler can be written to handle any class that
inherits from Throwable. If you write a handler for a node class (a class with
no subclasses), you've written a specialized handler: it will only handle
exceptions of that specific type. If you write a handler for a leaf class (a
class with subclasses), you've written a general handler: it will handle any
exception whose type is the node class or any of its subclasses. True or False?
If false, explain why.
A - False. "Leaf" and "node" are reversed in the
above statement. If you write a handler for a "leaf" class (a class
with no subclasses), you've written a specialized handler: it will only handle
exceptions of that specific type. If you write a handler for a "node"
class (a class with subclasses), you've written a general handler: it will
handle any exception whose type is the node class or any of its
subclasses."
Q - Java's finally block provides a mechanism that allows your method
to clean up after itself regardless of what happens within the try block. True
or False? If false, explain why.
A - True.
Q - Explain how you would specify that a method throws one or more
exceptions.
A - To specify that a method throws one or more exceptions, you add a
throws clause to the method signature for the method. The throws clause is
composed of the throws keyword followed by a comma-separated list of all the
exceptions thrown by that method.
Q - Provide a code fragment that illustrates how you would specify that
a method throws more than one exception.
A - See code fragment below.
void myMethod() throws
InterruptedException, MyException,
HerException,
UrException
{
//method body
}
Q - What type of argument is required by the throw statement?
A - The throw statement requires a single argument, which must be an
object derived either directly or indirectly
from the class Throwable.
Q - Some exception objects are automatically thrown by the system. It
is also possible for you to define your own exception classes, and to cause
objects of those classes to be thrown whenever an exception occurs. True or
False? If false, explain why.
A - True.
=======
Threads
Q - What is the definition of multi-threaded programming according to
Patrick Naughton?
A - According to The Java Handbook, by Patrick Naughton,
"Multi-threaded programming is a conceptual paradigm for
programming where you divide programs into two or more processes which can be
run in parallel."
Q - Multithreading refers to two or more programs executing,
"apparently" concurrently, under control of the operating system. The
programs need have no relationship with each other, other than the fact that
you want to start and run them all concurrently. True or False? If false,
explain why.
A - False. That is a description of multiprocessing, not multithreading.
Multithreading refers to two or more tasks executing, "apparently"
concurrently, within a single program.
Q - According to current terminology, the term blocked means that the
thread is waiting for something to happen and is not consuming computer
resources. True or False? If false, explain why.
A - True.
Q - What are the two ways to create threaded programs in Java?
A - In Java, there are two ways to create threaded programs:
Implement the Runnable
interface
Extend the Thread class
Q - What two steps are required to spawn a thread in Java?
A - The two steps necessary to spawn a thread in Java are:
instantiate an object of
type Thread and invoke its run() method.
Q - How do you start a thread actually running in Java?
A - Invoke the start() method on object of the Thread class or of a
subclass of the Thread class.
Q - It is always possible to extend the Thread class in your Java
applications and applets. True or False? If false, explain why.
A - False. Sometimes it is not possible to extend the Thread class,
because you must extend some other class and Java does not support multiple
inheritance.
Q - Although multithreaded programming in Java is possible, it is also
possible to write Java programs that do not involve threads: True or False? If
false, explain why.
A - False. The main method itself runs in a thread which is started by
the interpreter.
Q - What is the name of the method that can be used to determine if a
thread is alive?
A - The name of the method is isAlive().
Q - Once you start two or more threads running, unless you specify
otherwise, they run synchronously and independently of one another: True or
False? If false, explain why.
A - False. Once you start two or more threads running, unless you
specify otherwise, they run asynchronously and independently of one another.
Q - The process of keeping one thread from corrupting the data while it
is being processed by another thread is known as synchronization: True or
False? If false, explain why.
A - True.
Q - Java allows you to specify the absolute priority of each thread:
True or False? If false, explain why.
A - False. Java allows you to specify the priority of each thread
relative to other threads but not on an absolute basis.
Q - Thread synchronization can be achieved using wait(), notify(), and
notifyAll() which are methods of the Thread class: True or False? If false,
explain why.
A - False. wait(), notify(), and notifyAll() are not methods of the
Thread class, but rather are methods of the Object class.
Q - When you implement a threaded program, you will always override the
_____________ method of the Thread class and build the functionality of your
threaded program into that method. What is the name of the method?
A - The run() method.
Q - In a multithreaded program, you will start a thread running by
invoking the __________ method on your Thread object which will in turn invoke
the ___________ method. What are the names of the missing methods, and what are
the required parameters for each method?
A - In a multithreaded program, you will start a thread running by
invoking the start() method on your Thread object which will in turn invoke the
run() method. Neither method takes any parameters.
Q - What do Campione and Walrath list as the four possible states of a
thread?
A -
New Thread
Runnable
Not Runnable
Dead
Q - What methods can be invoked on a thread object which is in the
state that Campione and Walrath refer to as a New Thread and what will happen if
you invoke any other method on the thread?
A - When a thread is in this state, you can only start the thread or
stop it. Calling any method other than start() or stop() will cause an
IllegalThreadStateException.
Q - What, according to Campione and Walrath, will cause a thread to
become Not Runnable?
A - a thread becomes Not Runnable when one of the following four events
occurs:
Someone invokes its sleep()
method.
Someone invokes its
suspend() method.
The thread uses its wait()
method to wait on a condition variable.
The thread is blocking on
I/O.
Q1 - Three keywords are used in Java to
specify access control. What are they?
A - The three keywords used to specify
access control in Java are public, private, and protected.
Q2 - In Java, special access privileges are
afforded to other members of the same package: True or False? If false, explain
your answer.
A - True. In Java, special access
privileges are afforded to other members of the same package.
Q3 - In Java, class variables are often
used with the __________ keyword to create variables that act like constants.
A - The final keyword.
Q4 - In Java, the ___________ keyword is
used to declare a class variable.
A - The static keyword.
Q5 - In Java, the ___________ keyword is
used to declare a class method.
A - The static keyword.
Q6 - When you include a method in a Java
class definition without use of static keyword, this will result in objects of that class containing an
instance method: True or False? If false, explain why.
A 7- True.
Q8 - Normally each object contains its own
copy of each instance method: True or False?
A - False, multiple copies of the method do
not normally exist in memory.
Q9- When you invoke an instance method
using a specific object, if that method refers to instance variables of the
class, that method is caused to refer to the specific instance variables of the
specific object for which it was invoked: True or False? If false, explain why.
A - True.
Q10 - Instance methods are invoked in Java
using the name of the object, the colon, and the name of the method as shown below: True or False? If
false, explain why.
myObject:myInstanceMethod( )
A - False. Use the period or dot operator,
not the colon.
Q11 - Instance methods have access to both
instance variables and class variables in Java: True or False. If false,
explain why.
A - True.
Q12 - Class methods have access to both
instance variables and class variables in Java: True or False. If false,
explain why.
A - False. Class method can only access
other class members.
Q13 - What are the two most significant
characteristics of class methods?
A - 1. Class methods can only access other
class members. 2. Class methods can be accessed using only the name of the
class. An object of the class is not required to access class methods.
Q14 - In Java, a class method can be
invoked using the name of the class, the colon, and the name of the method as shown below: True or False? If
false, explain why.
MyClass:myClassMethod()
A - False. You must use the period or dot
operator, not the colon.
Q15 - What is meant by overloaded methods?
A - The term overloaded methods means that
two or more methods may have the same name so long as they have different
argument lists.
Q16 - If you overload a method name, the
compiler determines at run time, on the basis of the arguments provided to the
invocation of the method, which version of the method to call in that instance:
True or False? If false, explain why.
A - False. The determination is made at
compile time.
Q16 - A constructor is a special method
which is used to construct an object. A constructor always has the same name as
the class in which it is defined, and has no return type specified. True or
False? If false, explain why.
A - True.
Q17 - Constructors may be overloaded, so a
single class may have more than one constructor, all of which have the same
name, but different argument lists: True or False. If false, explain why.
A - True
Q18 - What is the purpose of a parameterized
constructor?
A - The purpose of a parameterized
constructor is to initialize the instance variables of an object when the
object is instantiated.
Q 19 - The same set of instance variables
can often be initialized in more than one way using overloaded constructors:
True or False? If false, explain why.
A - True.
Q20
- It is not necessary to provide a constructor in Java. True or False?
If false, explain why.
A - True. .
Q 21 You can think of the default
constructor as a constructor which doesn't take any parameters: True or False?
If false, explain why.
A - True.
Q 22- In Java, if you provide any
constructors, the default constructor is no longer provided automatically: True
or False? If false, explain why.
A - True.
Q 23- In Java, if you need both a
parameterized constructor and a constructor which doesn't take parameters
(often called a default constructor), you must provide them both: True or
False? If false,explain why.
A - True.
Q 24- In Java, you can instantiate objects
in static memory at compile time, or you can use the new operator to request
memory from the operating system at runtime and use the constructor to
instantiate the object in that memory: True or False? If false, explain why.
A - False. In Java, objects can only be
instantiated on the heap at runtime.
Q25 - Provide a code fragment consisting of
a single statement that illustrates how the constructor is typically used in
Java to declare, instantiate, and initialize an object. Assume a parameterized
constructor with three parameters of type int.
A - MyClass myObject = new MyClass(1,2,3);
Q26 - Provide a code fragment consisting of
a single statement that illustrates how the default constructor is typically
used in Java to declare and instantiate an object.
A - MyClass myObject = new MyClass();
Q 27- What are the three actions performed
by the following statement?
MyClass myObject = new MyClass(1,2,3);
A - This statement performs three actions
in one.
The object is declared by notifying the compiler of the name of the
object.
The object is instantiated by using the new operator to allocate memory
space to contain the new object.
The object is initialized by making a call to the constructor named
MyClass.
Q 28- In Java, if you attempt to instantiate
an object and the Java Virtual Machine cannot allocate the
requisite memory, the system will:
________________________________________.
A - Throw an OutOfMemoryError.
Q 29- The following is a valid method call:
True or False. If false, explain why.
obj.myFunction(new myClassConstructor(1,2,3) );//Java version
A - True.
Q30 - In Java, when a method begins
execution, all of the parameters are created as local automatic
variables: True or False? If false, explain
why.
A - True.
Q31 - In the following statement, an object
is instantiated and initialized and passed as a parameter to a
function. What will happen to that object
when the function terminates?
obj.myFunction(new myClassConstructor(1,2,3) );//Java version
A - It will become eligible for garbage
collection.
Q 32- In Java, you declare and implement a
constructor just like you would implement any other method in your class,
except that: _______________________________________________
A - you do not specify a return type and
must not include a return statement.
Q33 - The name of the constructor must be
the same as the name of the ___________________.
A - class.
Q 34- Usually in cases of inheritance, you
will want the subclass to cause the constructor for the superclass to execute
last to initialize those instance variables which derive from the
superclass:True or False? If false, explain why.
A - False. You will want the subclass to
cause the constructor for the superclass to execute first.
Q 35- Provide a code fragment that you would
include at the beginning of your constructor for a subclass to cause the
constructor for the superclass to be invoked prior to the execution of the body
of the constructor.
A - super(optional parameters);
Q 36- Every object has a finalize method
which is inherited from the class named ________________.
A - object.
Q 37- Before an object is reclaimed by the
garbage collector, the _______________ method for the
object is called.
A - finalize
Q 38- In Java, the destructor is always
called when an object goes out of scope: True or False? If false, explain why.
A - False. Java does not support the
concept of a destructor.
=====
Q 39- The class at the top of the
inheritance hierarchy is the Object class and this class is defined in the
package named java.Object: True or False? If false, explain why.
A - False. The Object class is defined in
the package named java.lang.
Q40 - We say that an object has state and
behavior: True or False? If false, explain why.
A - True.
Q 41- In Java, a method can be defined as
an empty method, normally indicating that it is intended to be overridden: True
or False? If false, explain why.
A - True.
Q 42- Including an empty method in a class
definition will make it impossible to instantiate an object of that class: True
or False.
A - False.
Q 43- A subclass can invoke the constructor
for the immediate superclass by causing the last line of of the subclass
constructor to contain the keyword super followed by a parameter list as though
calling a function named super() and the parameter list must match the method
signature of the superclass constructor: True or False? If false, explain why.
A - False. This can only be accomplished by
causing the first line of the constructor to contain the keyword super followed
by a parameter list as though calling a function named super(). The parameter
list must match the method signature of the superclass constructor.
Q 43 The equals() method is used to
determine if two reference variables point to the same object: True or False?
If false, explain why.
A- False. You can use the equals() method
to compare two objects for equality. You can use the equality operator (==) to
determine if two reference variables point to the same object.
Q 44- The equals() method is used to
determine if two separate objects are of the same type and contain the same
data. The method returns false if the objects are equal and true otherwise.
True or False? If false, explain why.
A - False. The method returns true if the
objects are equal and false otherwise.
Q 45 - The equals() method is defined in
the Object class: True or False? If false, explain why.
A - True.
Q 46- Your classes can override the
equals() method to make an appropriate comparison between two objects of a type
that you define: True or False? If false, explain why.
A - True.
Q 47- You must override the equals() method
to determine if two string objects contain the same data: True or False? If
false, explain why.
A - False. The system already knows how to
apply the equals() method to all of the standard classes and objects of which
the compiler has knowledge. For example, you can already use the method to test
two String objects or two array objects for equality.
Q 48- Given an object named obj1, provide a
code fragment that shows how to obtain the name of the class from which obj1
was instantiated and the name of the superclass of that class.
A - See code fragment below:
System.out.println("Name of class for obj1: " + obj1.getClass().getName());
System.out.println("Name of superclass for obj1: " + obj1.getClass().getSuperclass());
Q 49- Given an object named obj2, provide a
code fragment that shows how to use the newInstance() method to create a new
object of the same type
A - See code fragment below:
obj2 = obj1.getClass().newInstance();
Q 50- By overriding the getClass() method,
you can use that method to determine the name of the class from which an object
was instantiated: True or False? If false, explain why.
A - False. The getClass() method is a final
method and cannot be overridden.
Q 51- You must use the new operator to
instantiate an object of type Class: True or False? If false,explain why.
A - False. There is no public constructor
for the class Class. Class objects are constructed automatically by the
Java Virtual Machine as classes are loaded
and or by calls to the defineClass method in the class loader.
Q 52- The Class class provides a toString()
method which can be used to convert all objects known to the compiler to some
appropriate string representation. The actual string representation depends on
the type of object: True or False? If false, explain why.
A - False. The Object class (not the Class
class) provides a toString() method which can be used to convert all objects
known to the compiler to some appropriate string representation. The actual
string representation depends on the type of object.
Q 53- You can override the toString()
method of the Class class to cause it to convert objects of your design to
strings: True or False? If false, explain why.
A - False. The toString() method is a
method of the Object class, not the Class class.
Q 54- By default, all classes in Java are
either direct or indirect descendants of the Class class which is at the top of
the inheritance hierarchy: True or False? If false, explain why.
A - False. By default, all classes in Java
are either direct or indirect descendants of the Object class (not the Class
class) which is at the top of the inheritance hierarchy.
=====
Q 55 - To a limited extent, the interface
concept allows you to treat a number of objects, instantiated from different
classes, as if they were all of the same type: True or False? If false, explain
why.
A - True.
Q 56- At its simplest level, an interface
definition has a name, and declares one or more methods: True or False? If
false, explain why.
A - True.
Q57- In an interface definition, both the
method signatures and the actual implementations (bodies) of the methods are
provided: True or False? If false, explain why.
A - False. Only the method signatures are
provided. The actual implementations (bodies) of the methods are not provided.
Q 58- An interface definition can contain
only method declarations: True or False? If false, explain why.
A - False. In addition to method
declarations, an interface can also declare constants. Nothing else may be included
inside the body of an interface definition.
Q59 - If classes P, D, and Q all implement
interface X, a reference variable for an object of class P, D, or Q could be
assigned to a reference variable of type X: True or False? If false, explain
why.
A - True.
Q 60- If classes P, D, and Q all implement
interface X, then all of the methods declared in X must be exactly the same in
classes P, D, and Q: True or False? If false, explain why.
A - False. The interface simply declares
the signatures for methods. Classes that implement the interface are free to
provide a body for those methods which best suits the needs of the class.
Q 61- If classes P, D, and Q all implement
interface X a reference variable for an object of class P, D, or Q could be
assigned to a reference variable of type X and that reference variable could be
used to access all of the methods of the class (which are not excluded using
public, private, or protected): True or False? If false, explain why.
A - False. If one or more of the classes P,
D, and Q, define instance methods which are not declared in the interface X,
then a variable of type X cannot be used to access those instance methods.
Those methods can only be accessed using a reference variable of the class in
which the method is defined. Reference variables of the type X can only be used
to access methods declared in the interface X (or one of its superinterfaces).
Q 61 - The new operator must be used to
instantiate an object which is of the type of an interface: True or False? If
false, explain why.
A - False. Even though you can consider the
interface name as a type for purposes of storing references to objects, you
cannot instantiate an object of the interface type itself.
Q 63- One of the difficulties of
implementing interfaces is the requirement to coordinate the definition of
interface methods among the classes that implement the interface: True or
False? If false, explain why.
A - False. In defining interface methods,
each class defines the methods in a manner that is appropriate to its own class
without concern for how it is defined in other classes.
Q 64- As with classes, multiple interface
definitions can be combined into the same source file: True or False? If false,
explain why.
A- False. The compiler requires interface
definitions to be in separate files.
Q 65- List four ways in which interfaces
are useful:
A - See the following list:
To a limited extent, the interface
concept allows you to treat a number of objects, instantiated from different classes, as if they were all of the same type
Capturing similarities between unrelated classes without forcing a class
relationship
Declaring methods that one or more classes are expected to implement
Revealing an object's programming interface without revealing its class
(objects such as these are called
anonymous objects and can be useful when shipping a package of classes
to other developers)
Q 66- A minimum interface declaration
contains the Java keyword interface, the name of the interface, and the name of
the interface that it extends: True or False? If false, explain why.
A - False. A minimum interface declaration
contains the Java keyword interface and the name of the interface. There is no
requirement to specify the name of the interface that it extends, because it
may not extend another interface.
Q 67 - An interface can extend any number
of other interfaces: True or False? If false, explain why.
A - True.
Q 68- Just like a class definition can extend
any number of other classes, an interface can extend any number of other
interfaces: True or False? If false, explain why.
A - False. A class can extend only one
other class.
Q 69- An interface can extend any number of
other interfaces but not more than one class: True or False? If false, explain
why.
A - False. An interface cannot extend a
class.
Q 70- An interface inherits all constants
and methods from its superinterface: True or False? If false, explain why.
A - False. See reasons below:
An interface inherits all constants and
methods from its superinterface unless:
the interface hides a constant with another of the same name, or redeclares a method with a new method
declaration.
Q 71- The method declaration in an
interface consists of the method signature followed by a pair of
empty curly braces: True or False? If
false, explain why.
A - False. The method declaration is
terminated by a semicolon and no body (no curly braces) is provided for the
method.
Q 72- The keyword private is used to
restrict access to the members of an interface only to classes within the same
package: True or False? If false, explain why.
A - False. You may not use private in a
member declaration in an interface.
Q 73- All methods declared in an interface
are implicitly public and abstract: True or False? If false, explain why.
A - True.
Q 74- In addition to declaring methods, the
body of the interface may also define constants. Constant values defined in an
interface are implicitly public, static, and final: True or False? If false,
explain why.
A - True.
Q 75- You use an interface by defining a
class that extends the interface by name: True or False? If false, explain why.
A - False. You use an interface by defining
a class that implements (not extends) the interface by name.
Q 76- When a class claims to implement an
interface, it must provide a full definition for all the methods declared in
the interface as well as all of the methods declared in all of the superinterfaces
of that interface: True or False? If false, explain why.
A - True.
Q 77- A class can implement more than one
interface by including several interface names in a comma-separated list of
interface names, and by providing a full definition for all of the methods
declared in all of the interfaces listed as well as all of the superinterfaces
of those interfaces: True or False? If false, explain why.
A - True.
Q 78- Whenever a class implements an
interface, it is allowed to define only those methods declared in the
interface: True or False? If false, explain why.
A - False. Whenever a class implements an
interface, the class must define all of the methods declared in the interface,
but is also free to define other methods as well.
Q 79- The definition of an interface is a
definition of a new reference data type. You can use interface names just about
anywhere that you would use other type names, except that you cannot
____________________.
A - You cannot instantiate objects of the
interface type.
Q 80- Explain in your own words the
"bottom line" benefits of the use of an interface.
A - The interface makes it possible for a
method in one class to invoke methods on objects of other classes,
without the requirement to know the true
class of those objects, provided that those objects are all instantiated from
classes that implement one or more specified interfaces. In other words,
objects of classes that implement specified interfaces can be passed into
methods of other objects as the generic type Object, and the methods of the
other objects can invoke methods on the incoming objects by first casting them
as the interface type.
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