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

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

 

  1. Selection Statement :

There are two selection statements that Java supports:

  1. 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;

}

     Note:

  • condition is any expression that returns boolean value.
  • if statement works like as: If the condition is true the statement inside the if block is executed. Otherwise else block statement is 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

// initialization of vaiables

a=4;

b=5;

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.

Here is an example:

class  NestedIfs{

public static void main(String ar[]){

int a,b,i,j; // declaration of variables

// initialization of vaiables

a=4,b=5;

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);

}

}

  1. 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

}

      Note points:

  • 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”);

}

}

}

  1. Iteration Statement:

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

  1. 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–;

}

}

}

  1. for loop:

Syntax of for loop:

for( initialization; condition; iteration){

//body of for loop

}

     Note: points to be noted in for loop as:

  • 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 is executed.

For example:

class ForLoop{

public static void main(String ar[]){

int i;

for(i=0;i<6;i++){

       System.out.println(i);

}

}

}

  1. 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);

}

}

  1. Jump Statement:

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

     1. break:

break statement has three uses.

         a. it terminates a statement sequence in a switch statement.

b. it can be used to terminate a loop.

c. it can be 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 u have to notice that label the 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.

   2.  continue:

A continue statement causes control to be transferred directly to conditional expression that controls loop. here is an 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);

}

}

}

   3.  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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