Question 1

Which of the following method declarations are allowed inside interface?

Accepted Answer

Inside an interface every method will be by default abstract and public

Question 2

Why interface method is always public?

Accepted Answer

To make this method available to every implementation class

Question 3

Which among the following is a scope resolution operator?

Accepted Answer

:: is the scope resolution operator

Question 4

Which kind of inheritance is not supported directly through classes in java?

Accepted Answer

Multiple inheritance is not supported directly but it is achieved through the concept of Interface

Question 5

public class Threads2 implements Runnable { public void run() { System.out.println("run."); throw new RuntimeException("Problem"); Which among the following is true? } public static void main(String[] args) { Thread t = new Thread(new Threads2()); t…

Accepted Answer

Only D can be true

Question 6

public abstract class Shape { private int x; private int y; public abstract void draw(); public void setAnchor(int x, int y) { this.x = x; this.y = y; } } Which two classes use the Shape class correctly?

Accepted Answer

Only B is true

Question 7

public abstract class Shape { private int x; private int y; public abstract void draw(); public void setAnchor(int x, int y) { this.x = x; this.y = y; } } Which two classes use the Shape class correctly?

Accepted Answer

Only B is true

Question 8

X implements Y, Z Arguments: 1. X should be class 2. Y, Z should be interfaces

Accepted Answer

Both the statements are true

Question 9

What is a class, member and local variable?

Accepted Answer

Variables declared within a method are local variables Variables declared within the class are member variables Variables declared within the class with static modifier are class variables

Question 10

What is JDBC Driver ?

Accepted Answer

The JDBC Driver provides vendor-specific implementations of the abstract classes provided by the JDBC API This driver is used to connect to the database

Question 11

What are the steps required to execute a query in JDBC?

Accepted Answer

First we need to create an instance of a JDBC driver or load JDBC drivers, then we need to register this driver with DriverManager class Then we can open a connection By using this connection , we can create a statement object and this object will help us to execute the query

Question 12

What is the difference between a constructor and a method?

Accepted Answer

A constructor is a member function of a class that is used to create objects of that class It has the same name as the class itself, has no return type, and is invoked using the new operator We cannot invoke a constructor directly A method is an ordinary member function of a class It has its own name, a return type (which may be void), and is invoked using the dot operator

Question 13

What is an abstract class?

Accepted Answer

An abstract class is an incomplete class An abstract class is defined with the keyword abstract We cannot create an object of the abstract class because it is not complete It sets a behavioral protocol for all its child classes

Question 14

How will you define an abstract class?

Accepted Answer

An abstract class is defined with the keyword abstract Eg: public abstract class MyClass { }

Question 15

What is the difference between array and ArrayList ?

Accepted Answer

Array is collection of same data type Array size is fixed, It cannot be expanded But ArrayList is a growable collection of objectsArrayList is a part of Collections Framework and can work with only objects

Question 16

What is diamond problem?

Accepted Answer

The diamond problem is an ambiguity that can occur when a class multiply inherits from two classes that both descend from a common super class

Question 17

What is the security mechanism used in java?

Accepted Answer

Java uses sand box security model

Question 18

What is encapsulation?

Accepted Answer

Encapsulation describes the ability of an object to hide its data and methods from the rest of the world

Question 19

What is inheritance?

Accepted Answer

Inheritance is the ability to create new classes based on existing classes It is useful to reuse existing code

Question 20

Can we compile a java program without main?

Accepted Answer

Yes, we can In order to compile a java program, we don't require any main method But to execute a java program we must have a main in it (unless it is an applet or servlet) Because main is the starting point of a java program

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