For Loop in Java

Below point are for loop's control flow:

Switch statement

• The initialization procedure is carried out initially and only once. This step concludes with a semi colon and allows you to declare and initialise any loop control variables
• After initialization Statements,this is second condition where Boolean expression is executed each time to test the condition of the loop..
• If it is true,
  • Statements inside the body of for loop start executing
  • Then, statement of the for loop is executed till second condition get over. Here variable value is set to increased or decreased to met desire condition. It is an optional condition.
• The “for” loop terminates if the Boolean expression is false.

 for  (initialization expression, Boolean-expression , increment/decrement) { 

 // statements of for loop 

  } 

Flow Chart

 // java program using for loop  

public class Student { 
	public static void main(String[] args) {  		  
        int i;
        for(i = 1; i <= 10; i++)
        {
             System.out.println("2 * "+ i +"="+(2*i));
        }                    
    }  
}

2 * 1=2 

2 * 2=4 

2 * 3=6 

2 * 4=8 

2 * 5=10 

2 * 6=12 

2 * 7=14 

2 * 8=16 

2 * 9=18 

2 * 10=20 

Rules for using for Loops in Java

Let's learn about enum from below point

• Variable inside for loop condition must be same time
for(int a = 0, float b = 1; b < 4; b++)
if you write like this you will get compile time error like this "Syntax error on token "float", delete this token".
• Any variable that is declared inside a for loop cannot be accessed after the loop statement. Because this variable is declared within a block of statements, the body of the loop becomes its scope.

   // java program using for loop  

  public class Student { 
  	public static void main(String[] args) {  		  
  		    for(int i = 0; i < 10 ; i++)
  		    {
  		      System.out.println(i);
  		    }	    
  		    System.out.println( "Value of i is " +i );  //Accessing i outside for loop body gives an error                 
      }  
  }
  

  
  

  Output:

  Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
  	i cannot be resolved to a variable 

  Now variable can be accesed outside for loop

   // java program using for loop  

  public class Student { 
  	public static void main(String[] args) { 
           int i;
  	    for( i = 0; i < 10 ; i++)
  	    {
  	      System.out.println(i);
  	    }	    
  	   System.out.println( "Value of i is " +i );  //now accessing i outside for loop body will not  gives error                 
      }  
  } 
  

  
  

  Output:

  0 

  1 

  2 

  3 

  4 

  5 

  6 

  7 

  8 

  9 

  Value of i is 10 

• We can have multiple initializations in for loop. The commas should be used to separate these several expressions inside the for loop.


• Like initializations we may have multiple increment or decrement inside for loop with commas seprated.

   // java program using for loop  to show multiple initializations 

  public class Student { 
  	public static void main(String[] args) {     
          int a = 1; 
          for (int b = 0, c = 2; a < 5 && b < 5; a++, b++) {
              System.out.println("Value of b: "+b);         
          }
          System.out.println("Value of a: "+a);
      }  
  }  
  

  
  

  Output:

  Value of b: 0 

  Value of b: 1 

  Value of b: 2 

  Value of b: 3 

  Value of a: 5 

• Even if the variable has already been declared outside of the "for" loop, we can declare it again in the initialization block of the loop.

 //  Redeclaration of a variable 

public class Student { 
	public static void main(String[] args) {     
	    int a=10, b=10;  
	    for(a=1,b=0; a<5; a++,b++)
	    {
	      System.out.println("Value of a is: "+a);
	      System.out.println("Value of b is: "+b);
	    }
    }  
}  




Output:

Value of a is: 1 

Value of b IS : 0 

Value of a is: 2 

Value of b is: 1 

Value of a is: 3 

Value of b is: 2 

Value of a is: 4 

Value of b is: 3 

• we can skip any of the 3 condition in for loop. Let's see with example.

 //  Redeclaration of a variable 

public class Student { 
	public static void main(String[] args) {     
	    int i = 2, sum = 0 ;
	    for( ; i <= 20 ; sum +=i, i=2+i )
	    {
	    	 System.out.println(i);
	    }
       System.out.println("The sum of first 10 multiple of 2 is: " +sum) ;
    }  
}  




Output:

2 

4 

6 

8 

10 

12 

14 

16 

18 

20 

The sum of first 10 multiple of 2 is: 110 

• By removing the test-expression, we can also produce an infinite loop. Let's see with example.

 //  Redeclaration of a variable 

public class Student { 
	public static void main(String[] args) {     
        for( int x = 10 ;   ; x-- )
        {
        	System.out.println("This is an example of infinite for loop");
        }           
    }  
} 




Output:

This is an example of infinite for loop 

• we can have multiple statements inside for loop as well as null statement inside for loop.

Java for-each Loop:

• When traversing or iterating an Array or a Collection in Java, an Enhanced for loop is helpful. Due to the fact that we do not need to utilise a subscript notation or increment the value, it is simpler to use, write, and comprehend than a straightforward "for" loop.
• Instead of using the element's index, the for-each loop bases its work on the elements. The elements in the specified variable are returned one by one.

 for  (data_type variable_name: array_name) {

 //statements 

  } 

 // Java Loop program using for-each loop  

public class Student { 
	public static void main(String[] args) {     
        int arr[ ] = {5, 10, 15, 20, 25};
        for(int numDisplay : arr)
	    {
	      System.out.println(numDisplay+" ");
	    }          
    }  
}  

5 

10 

15 

20 

25 

Labeled for Loop in Java:

• The name of each Java "for" loop can be obtained using the Labeled for loop in Java. We add a label before the for loop to do this. If we have nested for loops, a labelled for loop is helpful so that we may break or continue from the specific for loop with the aid of the label.

labelname: 

 for  (initialization expression, Boolean-expression , increment/decrement) {

          //statements 

 } 

 // Java Loop program using for-each loop  

public class LabeledForExample
{
        public static void main(String[] args)
        {  
          xyz:   //Using Label for outer and for loop
            for(int a = 1; a <= 3; a++)
            {
              abc:
                for(int b = 1; b <= 3; b++)
                {
                  if(a==2 && b==2)
                  {
                    break xyz;
                  }
                  System.out.println(a+" "+b);
                }
            }
         }
    }
    

1 1 

1 2 

1 3 

2 1