Core Java - Interview Questions and Answers

61) is object cloning?

The object cloning is used to create the exact copy of an object. The clone() method of the Object class is used to clone an object. The java.lang.Cloneable interface must be implemented by the class whose object clone we want to create. If we don't implement Cloneable interface, clone() method generates CloneNotSupportedException.

62) What is method overloading?

Method overloading is the polymorphism technique which allows us to create multiple methods with the same name but different signature. We can achieve method overloading in two ways.

By Changing the number of arguments
By Changing the data type of arguments

Method overloading increases the readability of the program. Method overloading is performed to figure out the program quickly.

63) Why is method overloading not possible by changing the return type in java?

In Java, method overloading is not possible by changing the return type of the program due to avoid the ambiguity.

 class Adder{ static int add(int a,int b){return a+b;} static double add(int a,int b){return a+b;} } class TestOverloading3{ public static void main(String[] args){ System.out.println(Adder.add(11,11));//ambiguity }} 

Test it Now

Output:

 Compile Time Error: method add(int, int) is already defined in class Adder

64) Can we overload the methods by making them static?

No, We cannot overload the methods by just applying the static keyword to them(number of parameters and types are the same). Consider the following example.

 public class Animal {     void consume(int a)     {         System.out.println(a+" consumed!!");     }     static void consume(int a)     {         System.out.println("consumed static "+a);     }     public static void main (String args[])     {         Animal a = new Animal();         a.consume(10);         Animal.consume(20);     } }   

Output

 Animal.java:7: error: method consume(int) is already defined in class Animal     static void consume(int a)                 ^ Animal.java:15: error: non-static method consume(int) cannot be referenced from a static context         Animal.consume(20);               ^ 2 errors

65) Can we overload the main() method?

Yes, we can have any number of main methods in a Java program by using method overloading.

66) What is method overloading with type promotion?

By Type promotion is method overloading, we mean that one data type can be promoted to another implicitly if no exact matching is found.

Java Method Overloading with Type Promotion

As displayed in the above diagram, the byte can be promoted to short, int, long, float or double. The short datatype can be promoted to int, long, float or double. The char datatype can be promoted to int, long, float or double and so on. Consider the following example.

 class OverloadingCalculation1{   void sum(int a,long b){System.out.println(a+b);}   void sum(int a,int b,int c){System.out.println(a+b+c);}    public static void main(String args[]){   OverloadingCalculation1 obj=new OverloadingCalculation1();   obj.sum(20,20);//now second int literal will be promoted to long   obj.sum(20,20,20);   } } 

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Output

 40 60

67) What is method overriding:

If a subclass provides a specific implementation of a method that is already provided by its parent class, it is known as Method Overriding. It is used for runtime polymorphism and to implement the interface methods.

Rules for Method overriding

The method must have the same name as in the parent class.
The method must have the same signature as in the parent class.
Two classes must have an IS-A relationship between them.

68) Can we override the static method?

No, you can't override the static method because they are the part of the class, not the object.

69) Why can we not override static method?

It is because the static method is the part of the class, and it is bound with class whereas instance method is bound with the object, and static gets memory in class area, and instance gets memory in a heap.

70) Can we override the overloaded method?

Yes.

Interview :: Core Java