Q:
|
How can one prove that the array is not null but empty using one line of code? | |
A:
|
Print
args.length. It will print 0. That means it is empty. But if it would have
been null then it would have thrown a NullPointerException on attempting to
print args.length.
|
|
Q:
|
What environment variables do I need to set on my machine in order to be able to run Java programs? | |
A:
|
CLASSPATH
and PATH are the two variables.
|
|
Q:
|
Can an application have multiple classes having main method? | |
A:
|
Yes
it is possible. While starting the application we mention the class name to
be run. The JVM will look for the Main method only in the class whose name
you have mentioned. Hence there is not conflict amongst the multiple classes
having main method.
|
|
Q:
|
Can I have multiple main methods in the same class? | |
A:
|
No
the program fails to compile. The compiler says that the main method is
already defined in the class.
|
|
Q:
|
Do I need to import java.lang package any time? Why ? | |
A:
|
No.
It is by default loaded internally by the JVM.
|
|
Q:
|
Can I import same package/class twice? Will the JVM load the package twice at runtime? | |
A:
|
One
can import the same package or same class multiple times. Neither compiler
nor JVM complains abt it. And the JVM will internally load the class only
once no matter how many times you import the same class.
|
|
Q:
|
What are Checked and UnChecked Exception? |
A:
|
A
checked exception is some subclass of Exception (or Exception itself),
excluding class RuntimeException and its subclasses.
Making an exception checked forces client programmers to deal with the possibility that the exception will be thrown. eg, IOException thrown by java.io.FileInputStream's read() method· Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and its subclasses also are unchecked. With an unchecked exception, however, the compiler doesn't force client programmers either to catch the exception or declare it in a throws clause. In fact, client programmers may not even know that the exception could be thrown. eg, StringIndexOutOfBoundsException thrown by String's charAt() method· Checked exceptions must be caught at compile time. Runtime exceptions do not need to be. Errors often cannot be. |
Q:
|
What is Overriding? |
A:
|
When
a class defines a method using the same name, return type, and arguments as a
method in its superclass, the method in the class overrides the method in the
superclass.
When the method is invoked for an object of the class, it is the new definition of the method that is called, and not the method definition from superclass. Methods may be overridden to be more public, not more private. |
Q:
|
What are different types of inner classes? |
A:
|
Nested top-level classes, Member
classes, Local classes, Anonymous classes
Nested
top-level classes- If you declare a class within a class
and specify the static modifier, the compiler treats the class just like any
other top-level class.Any class outside the declaring class accesses the nested class with the declaring class name acting similarly to a package. eg, outer.inner. Top-level inner classes implicitly have access only to static variables.There can also be inner interfaces. All of these are of the nested top-level variety. Member classes - Member inner classes are just like other member methods and member variables and access to the member class is restricted, just like methods and variables. This means a public member class acts similarly to a nested top-level class. The primary difference between member classes and nested top-level classes is that member classes have access to the specific instance of the enclosing class. Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only within the block of their declaration. In order for the class to be useful beyond the declaration block, it would need to implement a more publicly available interface.Because local classes are not members, the modifiers public, protected, private, and static are not usable. Anonymous classes - Anonymous inner classes extend local inner classes one level further. As anonymous classes have no name, you cannot provide a constructor. |
Q:
|
Are the imports checked for validity at compile time? e.g. will the code containing an import such as java.lang.ABCD compile? | |
A:
|
Yes
the imports are checked for the semantic validity at compile time. The code
containing above line of import will not compile. It will throw an error
saying,can not resolve symbol
symbol : class ABCD location: package io import java.io.ABCD; |
|
Q:
|
Does importing a package imports the subpackages as well? e.g. Does importing com.MyTest.* also import com.MyTest.UnitTests.*? | |
A:
|
No
you will have to import the subpackages explicitly. Importing com.MyTest.*
will import classes in the package MyTest only. It will not import any class
in any of it's subpackage.
|
|
Q:
|
What is the difference between declaring a variable and defining a variable? | |
A:
|
In
declaration we just mention the type of the variable and it's name. We do not
initialize it. But defining means declaration + initialization.
e.g String s; is just a declaration while String s = new String ("abcd"); Or String s = "abcd"; are both definitions. |
|
Q:
|
What is the default value of an object reference declared as an instance variable? | |
A:
|
null
unless we define it explicitly.
|
|
Q:
|
Can a top level class be private or protected? | |
A:
|
No.
A top level class can not be private or protected. It can have either
"public" or no modifier. If it does not have a modifier it is
supposed to have a default access.If a top level class is declared as private
the compiler will complain that the "modifier private is not allowed
here". This means that a top level class can not be private. Same is the
case with protected.
|
|
Q:
|
What type of parameter passing does Java support? | |
A:
|
In
Java the arguments are always passed by value .
|
|
Q:
|
Primitive data types are passed by reference or pass by value? | |
A:
|
Primitive
data types are passed by value.
|
|
Q:
|
Objects are passed by value or by reference? | |
A:
|
Java
only supports pass by value. With objects, the object reference itself is
passed by value and so both the original reference and parameter copy both
refer to the same object .
|
|
Q:
|
What is serialization? | |
A:
|
Serialization
is a mechanism by which you can save the state of an object by converting it
to a byte stream.
|
|
Q:
|
How do I serialize an object to a file? | |
A:
|
The
class whose instances are to be serialized should implement an interface
Serializable. Then you pass the instance to the ObjectOutputStream which is
connected to a fileoutputstream. This will save the object to a file.
|
|
Q:
|
Which methods of Serializable interface should I implement? | |
A:
|
The
serializable interface is an empty interface, it does not contain any
methods. So we do not implement any methods.
|
|
Q:
|
How can I customize the seralization process? i.e. how can one have a control over the serialization process? | |
A:
|
Yes
it is possible to have control over serialization process. The class should
implement Externalizable interface. This interface contains two methods
namely readExternal and writeExternal. You should implement these methods and
write the logic for customizing the serialization process.
|
|
Q:
|
What is the common usage of serialization? | |
A:
|
Whenever
an object is to be sent over the network, objects need to be serialized.
Moreover if the state of an object is to be saved, objects need to be
serilazed.
|
|
Q:
|
What is Externalizable interface? | |
A:
|
Externalizable
is an interface which contains two methods readExternal and writeExternal.
These methods give you a control over the serialization mechanism. Thus if
your class implements this interface, you can customize the serialization
process by implementing these methods.
|
|
Q:
|
When you serialize an object, what happens to the object references included in the object? | |
A:
|
The
serialization mechanism generates an object graph for serialization. Thus it
determines whether the included object references are serializable or not.
This is a recursive process. Thus when an object is serialized, all the
included objects are also serialized alongwith the original obect.
|
|
Q:
|
Does Java provide any construct to find out the size of an object? | |
A:
|
No
there is not sizeof operator in Java. So there is not direct way to determine
the size of an object directly in Java.
|
|
Q:
|
Give a simplest way to find out the time a method takes for execution without using any profiling tool? | |
A:
|
Read
the system time just before the method is invoked and immediately after
method returns. Take the time difference, which will give you the time taken
by a method for execution.
To put it in code...long start = System.currentTimeMillis (); method (); long end = System.currentTimeMillis (); System.out.println ("Time taken for execution is " + (end - start)); Remember that if the time taken for execution is too small, it might show that it is taking zero milliseconds for execution. Try it on a method which is big enough, in the sense the one which is doing considerable amout of processing. |
|
Q:
|
What are wrapper classes? | |
A:
|
Java
provides specialized classes corresponding to each of the primitive data
types. These are called wrapper classes. They are e.g. Integer, Character,
Double etc.
|
|
Q:
|
Why do we need wrapper classes? | |
A:
|
It
is sometimes easier to deal with primitives as objects. Moreover most of the
collection classes store objects and not primitive data types. And also the
wrapper classes provide many utility methods also. Because of these resons we
need wrapper classes. And since we create instances of these classes we can
store them in any of the collection classes and pass them around as a
collection. Also we can pass them around as method parameters where a method
expects an object.
|
|
Q:
|
What are checked exceptions? | |
A:
|
Checked
exception are those which the Java compiler forces you to catch. e.g.
IOException are checked Exceptions.
|
|
Q:
|
What are runtime exceptions? | |
A:
|
Runtime
exceptions are those exceptions that are thrown at runtime because of either
wrong input data or because of wrong business logic etc. These are not
checked by the compiler at compile time.
|
|
Q:
|
What is the difference between error and an exception? | |
A:
|
An
error is an irrecoverable condition occurring at runtime. Such as OutOfMemory
error. These JVM errors and you can not repair them at runtime. While exceptions
are conditions that occur because of bad input etc. e.g.
FileNotFoundException will be thrown if the specified file does not exist. Or
a NullPointerException will take place if you try using a null reference. In
most of the cases it is possible to recover from an exception (probably by
giving user a feedback for entering proper values etc.).
|
|
Q:
|
How to create custom exceptions? | |
A:
|
Your
class should extend class Exception, or some more specific type thereof.
|
|
Q:
|
If I want an object of my class to be thrown as an exception object, what should I do? | |
A:
|
The
class should extend from Exception class. Or you can extend your class from
some more precise exception type also.
|
|
Q:
|
If my class already extends from some other class what should I do if I want an instance of my class to be thrown as an exception object? | |
A:
|
One
can not do anytihng in this scenarion. Because Java does not allow multiple
inheritance and does not provide any exception interface as well.
|
|
Q:
|
How does an exception permeate through the code? | |
A:
|
An
unhandled exception moves up the method stack in search of a matching When an
exception is thrown from a code which is wrapped in a try block followed by
one or more catch blocks, a search is made for matching catch block. If a
matching type is found then that block will be invoked. If a matching type is
not found then the exception moves up the method stack and reaches the caller
method. Same procedure is repeated if the caller method is included in a try
catch block. This process continues until a catch block handling the
appropriate type of exception is found. If it does not find such a block then
finally the program terminates.
|
|
Q:
|
What are the different ways to handle exceptions? | |
A:
|
There
are two ways to handle exceptions,
1. By wrapping the desired code in a try block followed by a catch block to catch the exceptions. and 2. List the desired exceptions in the throws clause of the method and let the caller of the method hadle those exceptions. |
|
Q:
|
What is the basic difference between the 2
approaches to exception handling. 1> try catch block and 2> specifying the candidate exceptions in the throws clause? When should you use which approach? |
|
A:
|
In
the first approach as a programmer of the method, you urself are dealing with
the exception. This is fine if you are in a best position to decide should be
done in case of an exception. Whereas if it is not the responsibility of the
method to deal with it's own exceptions, then do not use this approach. In
this case use the second approach. In the second approach we are forcing the
caller of the method to catch the exceptions, that the method is likely to
throw. This is often the approach library creators use. They list the
exception in the throws clause and we must catch them. You will find the same
approach throughout the java libraries we use.
|
|
Q:
|
Is it necessary that each try block must be followed by a catch block? | |
A:
|
It
is not necessary that each try block must be followed by a catch block. It
should be followed by either a catch block OR a finally block. And whatever
exceptions are likely to be thrown should be declared in the throws clause of
the method.
|
|
Q:
|
If I write return at the end of the try block, will the finally block still execute? | |
A:
|
Yes
even if you write return as the last statement in the try block and no
exception occurs, the finally block will execute. The finally block will
execute and then the control return.
|
|
Q:
|
If I write System.exit (0); at the end of the try block, will the finally block still execute? | |
A:
|
No
in this case the finally block will not execute because when you say
System.exit (0); the control immediately goes out of the program, and thus
finally never executes.
|
|
Q:
|
How are Observer and Observable used? | |
A:
|
Objects
that subclass the Observable class maintain a list of observers. When an
Observable object is updated it invokes the update() method of each of its
observers to notify the observers that it has changed state. The Observer
interface is implemented by objects that observe Observable objects.
|
|
Q:
|
What is synchronization and why is it important? | |
A:
|
With
respect to multithreading, synchronization is the capability to control
the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors. |
|
Q:
|
How does Java handle integer overflows and underflows? | |
A:
|
It
uses those low order bytes of the result that can fit into the size of the
type allowed by the operation.
|
|
Q:
|
Does garbage collection guarantee that a program will not run out of memory? | |
A:
|
Garbage
collection does not guarantee that a program will not run out of memory. It
is possible for programs to use up memory resources faster than they are
garbage collected. It is also possible for programs to create objects that
are not subject to garbage collection
. |
|
Q:
|
What is the difference between preemptive scheduling and time slicing? | |
A:
|
Under
preemptive scheduling, the highest priority task executes until it enters the
waiting or dead states or a higher priority task comes into existence. Under
time slicing, a task executes for a predefined slice of time and then
reenters the pool of ready tasks. The scheduler then determines which task
should execute next, based on priority and other factors.
|
|
Q:
|
When a thread is created and started, what is its initial state? | |
A:
|
A
thread is in the ready state after it has been created and started.
|
|
Q:
|
What is the purpose of finalization? | |
A:
|
The
purpose of finalization is to give an unreachable object the opportunity to
perform any cleanup processing before the object is garbage collected.
|
|
Q:
|
What is the Locale class? | |
A:
|
The
Locale class is used to tailor program output to the conventions of a
particular geographic, political, or cultural region.
|
|
Q:
|
What is the difference between a while statement and a do statement? | |
A:
|
A
while statement checks at the beginning of a loop to see whether the next
loop iteration should occur. A do statement checks at the end of a loop to
see whether the next iteration of a loop should occur. The do statement will
always execute the body of a loop at least once.
|
|
Q:
|
What is the difference between static and non-static variables? | |
A:
|
A
static variable is associated with the class as a whole rather than with
specific instances of a class. Non-static variables take on unique values
with each object instance.
|
|
Q:
|
How are this() and super() used with constructors? | |
A:
|
This()
is used to invoke a constructor of the same class. super() is used to invoke
a superclass constructor.
|
|
Q:
|
What are synchronized methods and synchronized statements? | |
A:
|
Synchronized
methods are methods that are used to control access to an object. A thread
only executes a synchronized method after it has acquired the lock for the
method's object or class. Synchronized statements are similar to synchronized
methods. A synchronized statement can only be executed after a thread has
acquired the lock for the object or class referenced in the synchronized
statement.
|
|
Q:
|
What is daemon thread and which method is used to create the daemon thread? | |
A:
|
Daemon
thread is a low priority thread which runs intermittently in the back ground
doing the garbage collection operation for the java runtime system. setDaemon
method is used to create a daemon thread.
|
|
Q:
|
Can applets communicate with each other? | |
A:
|
At
this point in time applets may communicate with other applets running in the
same virtual machine. If the applets are of the same class, they can
communicate via shared static variables. If the applets are of different
classes, then each will need a reference to the same class with static
variables. In any case the basic idea is to pass the information back and
forth through a static variable.
An applet can also get references to all other applets on the same page using the getApplets() method of java.applet.AppletContext. Once you get the reference to an applet, you can communicate with it by using its public members. It is conceivable to have applets in different virtual machines that talk to a server somewhere on the Internet and store any data that needs to be serialized there. Then, when another applet needs this data, it could connect to this same server. Implementing this is non-trivial. |
|
Q:
|
What are the steps in the JDBC connection? | |
A:
|
While making a JDBC connection we go through the following steps :
Class.forName(\"
driver classs for that specific database\" );Step 1 : Register the database driver by using : Step 2 : Now create a database connection using : Connection con = DriverManager.getConnection(url,username,password); Step 3: Now Create a query using : Statement stmt = Connection.Statement(\"select * from TABLE NAME\"); Step 4 : Exceute the query :
stmt.exceuteUpdate();
|
|
Q:
|
How does a try statement determine which catch clause should be used to handle an exception? | |
A:
|
When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exceptionis executed. The remaining catch clauses are ignored. | |
Q:
|
Can an unreachable object become reachable again? | |
A:
|
An
unreachable object may become reachable again. This can happen when the
object's finalize() method is invoked and the object performs an operation
which causes it to become accessible to reachable objects.
|
|
Q:
|
What method must be implemented by all threads? | |
A:
|
All
tasks must implement the run() method, whether they are a subclass of Thread
or implement the Runnable interface.
|
|
Q:
|
What are synchronized methods and synchronized statements? | |
A:
|
Synchronized
methods are methods that are used to control access to an object. A thread
only executes a synchronized method after it has acquired the lock for the
method's object or class. Synchronized statements are similar to synchronized
methods. A synchronized statement can only be executed after a thread has
acquired the lock for the object or class referenced in the synchronized
statement.
|
|
Q:
|
What is Externalizable? | |
A:
|
Externalizable
is an Interface that extends Serializable Interface. And sends data into
Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput
out) and readExternal(ObjectInput in)
|
|
Q:
|
What modifiers are allowed for methods in an Interface? | |
A:
|
Only public and
abstract modifiers are allowed for methods in interfaces.
|
|
Q:
|
What are some alternatives to inheritance? | |
A:
|
Delegation
is an alternative to inheritance. Delegation means that you include an
instance of another class as an instance variable, and forward messages to
the instance. It is often safer than inheritance because it forces you to
think about each message you forward, because the instance is of a known
class, rather than a new class, and because it doesn't force you to accept
all the methods of the super class: you can provide only the methods that
really make sense. On the other hand, it makes you write more code, and it is
harder to re-use (because it is not a subclass).
|
|
Q:
|
What does it mean that a method or field is "static"? | |
A:
|
Static
variables and methods are instantiated only once per class. In other words
they are class variables, not instance variables. If you change the value of
a static variable in a particular object, the value of that variable changes
for all instances of that class.
Static methods can be referenced with the
name of the class rather than the name of a particular object of the class
(though that works too). That's how library methods like System.out.println()
work out is a static field in the java.lang.System class.
|
|
Q:
|
What is the difference between preemptive scheduling and time slicing? | |
A:
|
Under
preemptive scheduling, the highest priority task executes until it enters the
waiting or dead states or a higher priority task comes into existence. Under
time slicing, a task executes for a predefined slice of time and then
reenters the pool of ready tasks. The scheduler then determines which task
should execute next, based on priority and other factors.
|
|
Q:
|
What is the catch or declare rule for method declarations? |
A:
|
If
a checked exception may be thrown within the body of a method, the method
must either catch the exception or declare it in its throws clause.
|
Q:
|
Is Empty .java file a valid source file? | |
A:
|
Yes,
an empty .java file is a perfectly valid source file.
|
|
Q:
|
Can a .java file contain more than one java classes? | |
A:
|
Yes,
a .java file contain more than one java classes, provided at the most one of
them is a public class.
|
|
Q:
|
Is String a primitive data type in Java? | |
A:
|
No
String is not a primitive data type in Java, even though it is one of the
most extensively used object. Strings in Java are instances of String class
defined in java.lang package.
|
|
Q:
|
Is main a keyword in Java? | |
A:
|
No,
main is not a keyword in Java.
|
|
Q:
|
Is next a keyword in Java? | |
A:
|
No,
next is not a keyword.
|
|
Q:
|
Is delete a keyword in Java? | |
A:
|
No,
delete is not a keyword in Java. Java does not make use of explicit
destructors the way C++ does.
|
|
Q:
|
Is exit a keyword in Java? | |
A:
|
No.
To exit a program explicitly you use exit method in System object.
|
|
Q:
|
What happens if you dont initialize an instance variable of any of the primitive types in Java? | |
A:
|
Java
by default initializes it to the default value for that primitive type. Thus
an int will be initialized to 0, a boolean will be initialized to false.
|
|
Q:
|
What will be the initial value of an object reference which is defined as an instance variable? | |
A:
|
The
object references are all initialized to null in Java. However in order to do
anything useful with these references, you must set them to a valid object,
else you will get NullPointerExceptions everywhere you try to use such
default initialized references.
|
|
Q:
|
What are the different scopes for Java variables? | |
A:
|
The
scope of a Java variable is determined by the context in which the variable
is declared. Thus a java variable can have one of the three scopes at any
given point in time.
1. Instance : - These are typical object level variables, they are initialized to default values at the time of creation of object, and remain accessible as long as the object accessible. 2. Local : - These are the variables that are defined within a method. They remain accessbile only during the course of method excecution. When the method finishes execution, these variables fall out of scope. 3. Static: - These are the class level variables. They are initialized when the class is loaded in JVM for the first time and remain there as long as the class remains loaded. They are not tied to any particular object instance. |
|
Q:
|
What is the default value of the local variables? | |
A:
|
The
local variables are not initialized to any default value, neither primitives
nor object references. If you try to use these variables without initializing
them explicitly, the java compiler will not compile the code. It will
complain abt the local varaible not being initilized..
|
|
Q:
|
How many objects are created in the following
piece of code? MyClass c1, c2, c3; c1 = new MyClass (); c3 = new MyClass (); |
|
A:
|
Only
2 objects are created, c1 and c3. The reference c2 is only declared and not
initialized.
|
|
Q:
|
Can a public class MyClass be defined in a source file named YourClass.java? | |
A:
|
No
the source file name, if it contains a public class, must be the same as the
public class name itself with a .java extension.
|
|
Q:
|
Can main method be declared final? | |
A:
|
Yes,
the main method can be declared final, in addition to being public static.
|
|
Q:
|
What will be the output of the following
statement? System.out.println ("1" + 3); |
|
A:
|
It
will print 13.
|
|
Q:
|
What will be the default values of all the elements of an array defined as an instance variable? |
A:
|
If
the array is an array of primitive types, then all the elements of the array
will be initialized to the default value corresponding to that primitive type.
e.g. All the elements of an array of int will be initialized to 0, while that
of boolean type will be initialized to false. Whereas if the array is an
array of references (of any type), all the elements will be initialized to
null.
|
- What is garbage collection? What is the process that is responsible for doing that in java? - Reclaiming the unused memory by the invalid objects. Garbage collector is responsible for this process
- What kind of thread is the Garbage collector thread? - It is a daemon thread.
- What is a daemon thread? - These are the threads which can run without user intervention. The JVM can exit when there are daemon thread by killing them abruptly.
- How will you invoke any external process in Java? - Runtime.getRuntime().exec(….)
- What is the finalize method do? - Before the invalid objects get garbage collected, the JVM give the user a chance to clean up some resources before it got garbage collected.
- What is mutable object and immutable object? - If a object value is changeable then we can call it as Mutable object. (Ex., StringBuffer, …) If you are not allowed to change the value of an object, it is immutable object. (Ex., String, Integer, Float, …)
- What is the basic difference between string and stringbuffer object? - String is an immutable object. StringBuffer is a mutable object.
- What is the purpose of Void class? - The Void class is an uninstantiable placeholder class to hold a reference to the Class object representing the primitive Java type void.
- What is reflection? - Reflection allows programmatic access to information about the fields, methods and constructors of loaded classes, and the use reflected fields, methods, and constructors to operate on their underlying counterparts on objects, within security restrictions.
- What is the base class for Error and Exception? - Throwable
- What is the byte range? -128 to 127
- What is the implementation of destroy method in java.. is it native or java code? - This method is not implemented.
- What is a package? - To group set of classes into a single unit is known as packaging. Packages provides wide namespace ability.
- What are the approaches that you will follow for making a program very efficient? - By avoiding too much of static methods avoiding the excessive and unnecessary use of synchronized methods Selection of related classes based on the application (meaning synchronized classes for multiuser and non-synchronized classes for single user) Usage of appropriate design patterns Using cache methodologies for remote invocations Avoiding creation of variables within a loop and lot more.
- What is a DatabaseMetaData? - Comprehensive information about the database as a whole.
- What is Locale? - A Locale object represents a specific geographical, political, or cultural region
- How will you load a specific locale? - Using ResourceBundle.getBundle(…);
- What is JIT and its use? - Really, just a very fast compiler… In this incarnation, pretty much a one-pass compiler — no offline computations. So you can’t look at the whole method, rank the expressions according to which ones are re-used the most, and then generate code. In theory terms, it’s an on-line problem.
- Is JVM a compiler or an interpreter? - Interpreter
- When you think about optimization, what is the best way to findout the time/memory consuming process? - Using profiler
- What is the purpose of assert keyword used in JDK1.4.x? - In order to validate certain expressions. It effectively replaces the if block and automatically throws the AssertionError on failure. This keyword should be used for the critical arguments. Meaning, without that the method does nothing.
- How will you get the platform dependent values like line separator, path separator, etc., ? - Using Sytem.getProperty(…) (line.separator, path.separator, …)
- What is skeleton and stub? what is the purpose of those? - Stub is a client side representation of the server, which takes care of communicating with the remote server. Skeleton is the server side representation. But that is no more in use… it is deprecated long before in JDK.
- What is the final keyword denotes? - final keyword denotes that it is the final implementation for that method or variable or class. You can’t override that method/variable/class any more.
- What is the significance of ListIterator? - You can iterate back and forth.
- What is the major difference between LinkedList and ArrayList? - LinkedList are meant for sequential accessing. ArrayList are meant for random accessing.
- What is nested class? - If all the methods of a inner class is static then it is a nested class.
- What is inner class? - If the methods of the inner class can only be accessed via the instance of the inner class, then it is called inner class.
- What is composition? - Holding the reference of the other class within some other class is known as composition.
- What is aggregation? - It is a special type of composition. If you expose all the methods of a composite class and route the method call to the composite method through its reference, then it is called aggregation.
- What are the methods in Object? - clone, equals, wait, finalize, getClass, hashCode, notify, notifyAll, toString
- Can you instantiate the Math class? - You can’t instantiate the math class. All the methods in this class are static. And the constructor is not public.
- What is singleton? - It is one of the design pattern. This falls in the creational pattern of the design pattern. There will be only one instance for that entire JVM. You can achieve this by having the private constructor in the class. For eg., public class Singleton { private static final Singleton s = new Singleton(); private Singleton() { } public static Singleton getInstance() { return s; } // all non static methods … }
- What is DriverManager? - The basic service to manage set of JDBC drivers.
- What is Class.forName() does and how it is useful? - It loads the class into the ClassLoader. It returns the Class. Using that you can get the instance ( “class-instance”.newInstance() ).
- Inq adds a question: Expain the reason for each keyword of
public static void main(String args[])
JAVA
No comments:
Post a Comment