What is the output of following program?

1. package com.javastepbystep;
2. 
   
3. class A
4. {
5.  
6.      static int method1(int i)
7.     {
8.          return method2(i *= 11);
9.      }
10.  
11.       static int method2(int i)
12.      {
13.           return method3(i /= 11);
14.       }
15.  
16.        static int method3(int i)
17.       {
18.            return method4(i -= 11);
19.       }
20.  
21.       static int method4(int i)
22.      {
23.          return i += 11;
24.      }
         
25.      public static void main(String [] args)
26.     {
27.           System.out.println(method1(11));
28.      }
29.  
30. }

Ans: 11

What is the output of following program?

 public class B{
    
      B b= new B();
    
     public int show(){
          return (true ? null : 0);
     }
    
     public static void main(String[] args)  {
    
            B b= new B();
            b.show();
        }
    
    }

Output:

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) 

Explanation:

• Whenever we create the object of any class constructor will be called first and memory allocated for all non-static variables
• Here  B b= new B(); the variable is an object and assigned to a new object of the same class
• B b= new B(); statement leads to recursive execution of constructor will create infinite objects so at the run time an exception will be raised
• Exception in thread "main" java.lang.StackOverflowError
• The common cause for a stack overflow exception is a bad recursive call. Typically this is caused when your recursive functions don't have the correct termination condition

Difference between == and .equals()

They both differ very much in their significance. equals() method is present in the java.lang.Object class and it is expected to check for the equivalence of the state of objects! That means, the contents of the objects.

Whereas the '==' operator is expected to check the actual object instances are same or not.

For example, lets say, you have two String objects and they are being pointed by two different reference variables s1 and s2.

 s1 = new String("abc");
 s2 = new String("abc");

Now, if you use the "equals()" method to check for their equivalence as

 if(s1.equals(s2))
      System.out.println("s1.equals(s2) is TRUE");
 else
      System.out.println("s1.equals(s2) is FALSE");

You will get the output as TRUE as the 'equals()' method check for the content equivality.

Lets check the '==' operator.

if(s1==s2)
     System.out.printlln("s1==s2 is TRUE");
   else
     System.out.println("s1==s2 is FALSE");

Now you will get the FALSE as output because both s1 and s2 are pointing to two different objects even though both of them share the same string content.

It is because of 'new String()' everytime a new object is created.

Try running the program without 'new String' and just with

   String s1 = "abc";
   String s2 = "abc";

You will get TRUE for both the tests.