There are mainly three categories of control statement in Java as:

  1. Selection Statement
  2. Iteration Statement
  3. Jump statement

§ Selection Statement:

There are two selection statements as:

if statement:


It is conditional branch statement. It can be used to route program execution through two different paths.

Syntax:  
if(condition) {
   statement;
} else{
   statement;
}

     Notes:

☛ condition is any expression that returns boolean value.

☛ If the condition is true then statement inside the if block will be execute. Otherwise else block statement will get  executed.

☛ There is no case when both block will be executed.

      For example:

class If{
   public static void main(String ar[]){
       int a,b; // declaration of variables
       a=4; b=5; // initialization of vaiables

       if(a<b){
          a=0;
          System.out.println(a);
       } // end of if block
       else{
         b=0;
         System.out.println(b);
       }//end of else block
    }
}

     Nested ifs: 

Nested ifs itself have many if statements.

For example:

class NestedIfs{
   public static void main(String ar[]){
     int a,b,i,j; // declaration of variables
     a=4,b=5; // initialization of vaiables

     if(a<0){
       if(b>20){
         i=10;
         System.out.println(i);
       }
       if(b==20){
         j=120;
         System.out.println(j);
       }else{
         i=9;j=12;
      }
    } // end of if block
   else{
     b=0;
     System.out.println(b);
   }//end of else block
 }
}

    if-else-if ladder:

it is based upon the sequence of nested ifs. Here is syntax of if-else-if;

if(condition){ Statement;}
else if(condition){statement; }
else if(condition){statement;}
...
else{ statement;}

    Notes:

☛ Every if condition is checked. if condition is true then only that if block will be executed and all if conditions are   bypassed.

☛ If none of if condition is true then final else block will be executed.

For example:

class ifElseIf{
   public static void main(String ar[]){
     int month=4;
     String season;

     if(month==12 || month==1 || month==2){
        season=”winter”;
     } else if(month==3 || month==4 || month==5){
        season=”spring”;
     } else if(month==6 || month==7 || month==8){
         season=”summer”;
     } else if(month==9 || month==10 || month==11){
         season=”Autumn”;
     } else{
         season=”bogus month”
     }

    System.out.println(season);
  }
}

switch statement:


switch statement provides an easy way to dispatch execution to different part of the code based on the value of expression.

Syntax of switch statement:

switch(expression){
  case value1:
     //statement sequence
     break;
  case value2:
    //statement sequence
    break;
  ...
  default:
    //default statement sequence
}

      Notes:

☛ Each of the values specified in the case statement must be type compatible with the expression.

☛ The value of the expression is matched with each of literal value in case statement. If match found, the code  sequence of case statement is executed.

☛ If none of the constant matches value of expression then default case statement is executed.

☛ The break statement is used inside switch to terminate the execution and jump out of the switch.

For example:

class Switch{
   public static void main(String ar[]){
      int i=1;
      
      switch(i){
        case 1: 
            System.out.println(“i is less than 10”);
            break;
        case 2: 
            System.out.println(“I is greator than 10”);
            break;
        case 3: 
            System.out.println(“I is equal to the 10”);
            break;
        default:
           System.out.println(“none of the above condition”);
     }
  }
}

§ Iteration Statement:

Iteration statements are for, while, do-while. These statements are used for creating loops.

while loop:


It repeats a statement or block while its controlling expression (condition) is true. Here is syntax:

while(condition){
  // body of loop
}

For Example:

class While{
   public static void main(String ar[]){
     int n=10,m=12;

     while(n<m){
       System.out.println(m+” is greator than ”+ n);
       m--;
     }
  }
}

for loop:


Syntax of for loop:

for( initialization; condition; iteration){
   //body of for loop
}

     Notes:

☛ When the loop starts, the initialization portion executes. And the initialization expression is executed only once.

☛ Next condition is evaluated. If this condition is true, then the body of loop is executed.

☛ If condition is false then loop terminates.

☛ Next iteration portion of loop will be executed.

   For example:

class ForLoop{
  public static void main(String ar[]){
    int i;

    for(i=0;i<6;i++){
       System.out.println(i);
    }
  }
}

do-while loop:


The do-while loop always executes its body at least once, because its conditional expression is at the bottom of the loop. Here is syntax:

do{
   //body of loop
} while(condition);

For example:

class DoWhile{
  public static void main(String ar[]){
    int i=1;

    do{
       System.out.println(i);
       i++;
    }
    While(i<5);
  }
}

§ Jump Statement:

It supports three jump statements are as : break, continue, return. these statements are used to throw or transfer control from a part of code to another portion.

break:


break statement has three uses.

  • Terminates a statement sequence in a switch statement.
  • Used to terminate a loop.
  • Used as goto.

    here is an example for using break as a goto statement:

class BreakAsGoto{
   public static void main(String ar[]){
     outer: for(int i=0;i<2;i++){
       if(i==1){
         break outer;//exit from both loop
       }
       System.out.println("i = "+i);
     }
    System.out.println("loop completes");
  }
}

Note:

      ☛ When the inner loop breaks to outer loop, both loop have been terminated.

☛ Here if you have noticed that label for statement is must as it has a block of code as its target. and you can not  break any label which is not defined for an enclosing block.

continue:


A continue statement causes control to be transferred directly to conditional expression that controls loop.

For example:

class Continue{
   public static void main(String ar[]){
     for(int i=0; i<9;i++){
        System.out.println(i);

        if(i<9){
          continue;
        }
       System.out.println("i is greator than "+i);
    }
  }
}

    return:


The return statement is used to explicitly return from a method. And it causes program control to return to the caller of that method.

For example:

class Return{
   public static void main(String ar[]){
     boolean t=true;
     System.out.println("before return");

     if(t){
       return;
     }

    System.out.println("After Return"); //this line never executes 
          //because if statement is true then  return statement is      
          // executed and it return to the caller of this method. 
          //and an error "unreachable code" will be thrown.
  }
}

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