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 Java Questions

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Q:

In RDBMS, what is the efficient data structure used in the internal storage representation?

A) Stack B) Queue
C) B+ tree structure D) AVL tree Structure
 
Answer & Explanation Answer: C) B+ tree structure

Explanation:

B+ tree. Because in B+ tree, all the data is stored only in leaf nodes, that makes searching easier. This corresponds to the records that shall be stored in leaf nodes

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Q:

What are the restriction imposed on a static method or a static block of code?

Answer A static method should not refer to instance variables without creating an instance and cannot use "this" operator to refer the instance.
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Q:

Which of the following are incorrect form of StringBuffer class constructor  ?

A) StringBuffer(int size , String str) B) StringBuffer(int size)
C) StringBuffer(String str) D) StringBuffer()
 
Answer & Explanation Answer: A) StringBuffer(int size , String str)

Explanation:
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Q:

Which two method you need to implement for key Object in HashMap ?

Answer

In order to use any object as Key in HashMap, it must implements equals and hashcode method in Java.

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Q:

Which is true?

A) "X extends Y" is correct if and only if X is a class and Y is an interface B) "X extends Y" is correct if and only if X is a class and Y is an interface
C) "X extends Y" is correct if X and Y are either both classes or both interfaces D) "X extends Y" is correct for all combinations of X and Y being classes and/or interfaces
 
Answer & Explanation Answer: C) "X extends Y" is correct if X and Y are either both classes or both interfaces

Explanation:

A is incorrect because classes implement interfaces, they don't extend them. B is incorrect because interfaces only "inherit from" other interfaces. D is incorrect based on the preceding rules.

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Q:

Which of these class have only one field 'TYPE' ?

A) Run time B) Process
C) Void D) System
 
Answer & Explanation Answer: C) Void

Explanation:

The Void class has one field, TYPE, which holds a reference to the Class object for the type void.

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Q:

Which containers use a border Layout as their default layout ?

Answer

The window, Frame and Dialog classes use a border layout as their default layout.

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Q:

I don't want my class to be inherited by any other class. What should i do?

Answer

You should declared your class as final. But you can't define your class as final, if it is an abstract class. A class declared as final can't be extended by any other class.

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