Q) What is the difference between equals() and == ?

Ans) == operator is used to compare the references of the objects. 
public bollean equals(Object o) is the method provided by the Object class. The default implementation uses == operator to compare two objects. But since the method can be overriden like for String class. equals() method can be used to compare the values of two objects.

String str1 = "MyName"; 
String str2 = "MyName";
String str3 = new String(str2);

if (str1 == str2) {
  System.out.println("Objects are equal")
}else{
  System.out.println("Objects are not equal")
}
if(str1.equals(str2)) {
  System.out.println("Objects are equal")
} else {
  System.out.println("Objects are not equal")
}

Output:
Objects are not equal
Objects are equal

String str2 = "MyName";
String str3 = str2;
if (str2 == str3) {
System.out.println("Objects are equal")
}else{
System.out.println("Objects are not equal")
}
if (str3.equals(str2)) {
  System.out.println("Objects are equal")
} else {
  System.out.println("Objects are not equal")
}

Output:
Objects are equal
Objects are equal

Immutable class:

 

• Make class final so that it should not be inherited.
• All the variables should be private so should not be accessible outside of class. 
• Make all variables final so that value can not be changed.
• A constructor to assign values to variables in class.
• Do not add any setter methods.

Java Interview Program to Swap two numbers without using third variable in java

1. public class SwapTwoNumbers {
2.  
3. public static void main(String[] args) {
4.  
5. int number1=20;
6. int number2=30;
7.  
8. System.out.println("Before Swapping");
9. System.out.println("Value of number1 is :" + number1);
10. System.out.println("Value of number2 is :" +number2); 
11.  
12. number1=number1+number2;
13. number2=number1-number2;
14. number1=number1-number2;
15.  
16. System.out.println("After Swapping");
17. System.out.println("Value of number1 is :" + number1);
18. System.out.println("Value of number2 is :" +number2);
19.  
20. }
21. }

1. public class SwapTwoNumbers {
2.  
3. public static void main(String[] args) {
4.  
5. int number1=2;
6. int number2=4;
7.  
8. System.out.println("Before Swapping");
9. System.out.println("Value of number1 is :" + number1);
10. System.out.println("Value of number2 is :" +number2); 
11.  
12. number1=number1^number2;
13. number2=number1^number2;
14. number1=number1^number2;
15.  
16. System.out.println("After Swapping");
17. System.out.println("Value of number1 is :" + number1);
18. System.out.println("Value of number2 is :" +number2);
19.  
20. }
21. }

Java programming examples: Hashmap

Java programming examples: Hashmap

1. public class HashMapJavaTricky{
2.  
3. public static void main(String[] args) {
4.  
5.     HashMap<Integer,String> hm= new HashMap<Integer, String>();  
6. 
   
7.      hm.put(1, "one");
8.      hm.put(2, "two");
9.      hm.put(3, "three");
10.  
11.      hm.put(1, "ONE");
12.      hm.put(null,null);
13.  
14.     System.out.println(hm.size()); 
15.  
16. for (Integer name: hm.keySet()){
17.  
18.    System.out.println(name + " " + hm.get(name)); 
19.   
20. }
21.  
22. }
23. }

 

1. 4
2. null null
3. 1 ONE
4. 2 two
5. 3 three

Java interview Program to find second Smallest number in an integer array by sorting the elements.

class SecondSmallestNumber{

public static void main(String args[])
{

int numbers[] = {6,3,37,12,46,5,64,21};

  Arrays.sort(numbers);

  System.out.println("Smallest Number: "+numbers[0]);
  System.out.println("Second Smallest Number: "+numbers[1]);

 }

}

Java interview Program to find second smallest number in an integer array without sorting the elements.
class SecondSmallestNumber{

int[] x ={10,11,12,13,14,6,3,-1};

        int small=x[0];

 for(int i=0;i<x.length;i++)
 {
        if(x[i]<small)
        {
        small=x[i];
        }
 }

   int sec_Small=x[0];

for(int i=0;i<x.length;i++)
 {
        if(x[i]<sec_Small && x[i]!=small)
        {
        sec_Small=x[i];
        }
  }

        System.out.println("Second Smallest Number: "sec_Small);
        }
}

Program to print prime numbers in java

public class primenumbers {

public static void main(String[] args) {

int num=50;
int count=0;

for(int i=2;i<=num;i++){

count=0;

for(int j=2;j<=i/2;j++){

if(i%j==0){
count++;
break;
}

}

if(count==0){

System.out.println(i);

}

}

}

}

What is the output of following program?

 What is the output of following program?

1. package com.instanceofjava;
2.  
3. public class B{
4.  
5.   B b= new B();
6.  
7.  public int show(){
8.       return (true ? null : 0);
9.  }
10.  
11.  public static void main(String[] args)  {
12.  
13.         B b= new B();
14.         b.show();
15.     }
16.  
17. }

 

1. Exception in thread "main" java.lang.StackOverflowError
2. at com.instanceofjava.B.<init>(B.java:3)
3. at com.instanceofjava.B.<init>(B.java:5)
4. at com.instanceofjava.B.<init>(B.java:5)