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 Q571. Is it mandatory to have a default constructor ?Core Java
Ans. No.

Default constructor is provided by compiler if no constructor is provided ( argument or no argument ) by us.

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 Q572. Which environment variables do we need to set in order to run Java programs?Core Java
Ans. PATH, CLASSPATH and JAVA_HOME

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   Like         Discuss         Correct / Improve     environment variables  path  classpath  java_home     Asked in 3 Companies      basic        frequent

 Q573. Can an application have multiple main methods within different classes ? If yes, How will the app decide which one to be executed ?Core Java
Ans. Yes we can have a main method with string[] argument in every class of an application. When we execute an app we specify the starting point i.e the class that will get the control first and hence main method of that class gets executed.

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   Like         Discuss         Correct / Improve     main method     Asked in 3 Companies

 Q574. Does importing a package imports all its sub packages too ?Core Java
Ans. No, but we can use wild card (*) to do so

For example -

import java.util.*

will import all packages with name starting with java.util

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   Like         Discuss         Correct / Improve     package   import packages     Asked in 1 Companies      basic

 Q575. What is the default value of a declared object reference ?Core Java
Ans. Null

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   Like         Discuss         Correct / Improve     object reference  null     Asked in 1 Companies      basic

 Q576. Is there a way to know size of an object in Java ?Core Java
Ans. No, Java doesn't have a sizeOf operator. In C / C++ , its required to determine how much memory allocation is required which is not the case with Java. Java handles memory allocation and deallocation intrinsically.

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   Like         Discuss         Correct / Improve     sizeOf  size of object  sizeOf operator     Asked in 1 Companies        rare

 Q577. What are the different ways to handle an exception ?Core Java
Ans. 1. Wrap the desired code in try block followed by a catch / finally to catch the exception

2. Declare the throws clause with exceptions that the code is expected to throw as an indication to the calling method to take care of it.

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 Q578. How does Java handle integer overflows and underflows?Core Java
Ans. It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

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 Q579. Is delete a keyword in Java ?Core Java
Ans. No, delete is not a keyword in Java. Destruction of objects is taken care by Java Garbage Collection mechanism.

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 Q580. Is exit a keyword in Java ?Core Java
Ans. No exit is a method to exit execution of a program.

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 Q581. Who invokes a thread's run method ?Core Java
Ans. After a thread is started using a call to start method, JVM invokes the thread’s run method when the thread is initially executed.

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 Q582. What is nested interface?Core Java
Ans. Interface that is declared inside the interface or class, is known as nested interface. It is static by default.

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 Q583. What kind of thread is garbage collection thread ?Core Java
Ans. Daemon thread

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 Q584. What is the difference between the Reader/Writer java.io hierarchy and the Stream class hierarchy?Core Java
Ans. The Reader/Writer hierarchy is character oriented, whereas the Stream class hierarchy is byte oriented.

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   Like         Discuss         Correct / Improve     java io  streams      intermediate

 Q585. What is an IO Filter ?Core Java
Ans. It's an object that reads from one stream and writes to another.

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   Like         Discuss         Correct / Improve     java io  io filter      intermediate

 Q586. Difference between shallow copy and object cloning ?Core Java
Ans. Shallow copy is one of the way for object cloning, other being deep copy.

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   Like         Discuss         Correct / Improve     cloning  shallow copy  object cloning      basic

 Q587. What is Shutdown hook ?Core Java
Ans. Shutdown hook is a thread that is invoked before the JVM is shut down. we can use it perform resource cleaning task.

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 Q588. how to access the methods of an inner class?Core Java
Ans. It depends on the type of inner class

To access non static inner class method

new OuterClass().new InnerClass().getMethod();

To access static method of static inner class

new OuterClass.InnerClass().getMethod();

  Sample Code for inner class

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   Like         Discuss         Correct / Improve     inner classes  nested aclasses     Asked in 1 Companies      Intermediate        frequent

 Q589. Which memory segment holds String Pool in Java ?Core Java
Ans. String Pool resides in runtime constant Pool which is a part of Heap memory segment.

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 Q590. What are the cursors available in Java ?Core Java
Ans. Enumeration
Iterator
List iterator

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 Q591. How can be restrict creation of more than n objects in Java ?Core Java
Ans. We can follow the same design which we follow in singleton Classes. We can have a static counter that will keep the count of number of objects already created, We can keep the constructor private and being called through the static method. We can keep incrementing the counter before calling the constructor and put a check to call only if it's lesser than n.

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 Q592. Do you feel that its useless to define hashCode method for a class ?Core Java
Ans. Yes its useless if we are not going to use its objects within Hash collection, For example - HashSet , HashMap. HashCode is used internally by these collections for Search.

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   Like         Discuss         Correct / Improve     hashcode  hash collections  search

 Q593. What is a class and object ?

or

How would you explain a fresher the concept of class and object in simple terms ?		Core Java
Ans. Class is a template using which objects are created in memory. It's kind of a mold using which objects with body / state are made.


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   Like         Discuss         Correct / Improve     class  object  class vs object     Asked in 4 Companies      basic        frequent

 Q594. Explain dot(.) operator ?Core Java
Ans. Its used to access the object properties using the object reference or class properties using the Class Name. Moreover its used to access the classes and Interfaces of a package.

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   Like         Discuss         Correct / Improve     operators

 Q595. Does Java supports Default arguments ?Core Java
Ans. No

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 Q596. Can we have only try block in java ?Core Java
Ans. No, It should be followed by either catch or finally.

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 Q597. What is memory leak ? How Java helps countering memory leaks compared to C++ ?Core Java
Ans. Memory Leak is a situation wherein we have a reserved memory location but the program has lost its reference and hence has no way to access it.

Java doesn't have concept of Pointers, Moreover Java has concept of Garbage collection that frees up space in heap that has lost its references.

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   Like         Discuss         Correct / Improve     memory leak  garbage collection      intermediate        frequent

 Q598. What are the benefits of creating immutable objects ?Core Java
Ans. 1. Security and Safety - They can be shared across multiple threads as they are thread safe. Moreover, it protects then from bad state due to interception by the other code segment. One such problem due to mutability and access by alternate code segment could be the change of hash code and then the impact on its search with hash collections.

2. Reuse - In some cases they can be reused as only one copy would exist and hence it can be relied upon. For example - String Pool

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   Like         Discuss         Correct / Improve     immutable  immutability objects     Asked in 1 Companies      Intermediate        frequent

 Q599. What is the difference between

File f = new File("homexyz.txt");

and

File f = File.createTempFile("xyz",".txt","home"); ?		Core Java
Ans. First will not create physical file in storage whereas the second will.

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 Q600. What is an applet ?Core Java
Ans. Applet is a J2EE component or a tiny application that gets executed in a widget engine ( like browser )

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