Java-for( ) loop / Chapter -5/Flow Control

c. for ( ) loop :- 

• If we know the number of iterations in advance then we should use for ( ) loop. 
• It is the most commonly used loop in java.
• Curly braces{ } are optional and without Curly braces { } we can take one statement under while which should not be the declarative statement.

Syntax:-

                                                
(a) initialization section;-

• This part will be executed only once in the whole life cycle of the for() loop. Here we can declare and  initialize a local variable.we can declare any number of variable but they should be the same type . If we are trying to declare different data type then we will get compile time error. Re declaration is also not allowed. 

example:
int i=0, j=0;             valid
int i=0, String s ="javabychetan";             invalid  (different data type)
int i=0,int j=0;                                          invalid ( Re declaration is not allowed)

• In the initialization section, we can take any valid java statement including 'System.out.println' also.

 example:-
                int i=0;
for(System.out.println("you are reading javabychetan");i<3:;i++)
{

             System.out.println("you are reading javabychetan");                valid

}

(b) condition-check section;-

• Here we can take any valid java expression but this should always be of the boolean type .
• This section is optional.
• We can leave it blank and  in this condition compiler will always place true here.

(c) Increment / Decrement section:-

•  In the increment-decrement section we can take any valid java statement including System.out.println( ).

 example:-
                int i=0;
for(System.out.println("Hello");i<3:;System.out.println("Hii"))
{
               i++;                                                              valid

}
output is                 Hello
                              Hii
                              Hii
                              Hii
                     
Note: All three parts of for( ) loop are independent of each other and optional.
for( ;  ; )
{ 
             (System.out.println("Hello");  
}

Output :  This Is Infinite loop and Hello will be printed for infinite times.

              Important Loop Holes

example 1:-
 
for(int i=0 ; true ; i++)
{
    System.out.println(" javabychetan");        
}
 System.out.println("JAVA");
      ↑
      invalid
 Compile Time Error: Unreachable state


example 2:-
 
for(int i=0 ; false ; i++)
{
 ↑     System.out.println(" javabychetan");        
   }
 System.out.println("JAVA");

      invalid
 Compile Time Error: Unreachable state

example 3:-
 
for(int i=0 ; ; i++)
{
    System.out.println(" javabychetan");        
}
 System.out.println("JAVA");
      ↑
      invalid
 Compile Time Error: Unreachable state


example 4:-
 
int i=10,j=20;
for(int x=0 ; i < j ; x++)
{
    System.out.println(" javabychetan");        
}
 System.out.println("JAVA");

     Output is:-      javabychetan
                        javabychetan
                        javabychetan  .........(infinite times)

example 5:-
 
int i=10,j=20;
for(int x=0 ; i > j ; x++)
{
    System.out.println(" javabychetan");        
}
 System.out.println("JAVA");

Output is:-     JAVA


example 6:-
 
final int i=10,j=20;
for(int x=0 ; i < j ; x++)
{
    System.out.println(" javabychetan");        
}
 System.out.println("JAVA");
  ↑
      invalid
 Compile Time Error: Unreachable state



example 7:-
 
final int i=10,j=20;
for(int x=0 ; i > j ; x++)
{
 ↑   System.out.println(" javabychetan");        
      }
  System.out.println("JAVA");
  
      invalid

 Compile Time Error: Unreachable state


Next:Chapter -6/Flow Control/ for each loop
Back:Chapter -4/Flow Control/ do-while () loop