Control Statements in java

           The control statement are used to controll the flow of execution of the program .

This execution order depends on the supplied data values and the conditional logic.

Java contains the following types of control statements. .

1- Selection Statements:

               Selection statements allow your program to choose different paths of

 execution based upon the outcome of an expression or the state of a variable Java

supports two selection statements, "if and switch".

   a: If Statement:

          It can be used to route program execution through two different paths.

          This is a control statement to execute a single statement or a block of code,

            when the given condition is true and if it is false then it skips if block and rest code of program is executed .

  Syntax:

if(condition)   { <statement1>;   }   else   {   <statement2>;   }

              If the condition is true, then statement1 is executed. Otherwise, statement2 (if it exists) is executed.

Example:

if(a>b)   {   System.out.println("a is greater than b");// prints a is greater than b   }   else   {    System.out.println("b is greater than a");//prints b is greater than a   }

   if-else-if Ladder

When there are more than two conditions then a common programming construct that is based upon a sequence of nested ifs called if-else-if ladder is used. It looks like this:

 

if(condition)      <statement>;    else if(condition)      <statement>;    else if(condition)      <statement>;        ...     else      <statement>;

 b.Switch statement:

       Switch statement provides a better alternative than a large series of if-else-if statements.This is an easier implementation to the if-else statements. The keyword "switch" is followed by an expression that should evaluates to byte, short, char or int primitive data types ,only.

General Syntax:

  

switch (x) {     case value0:     doSomething0();     break;   case value1:     doSomething1();     break;   case value2:     doSomething2();     break;  case value3:     doSomething3();     break;   case value4:     doSomething4();     break;     ....     ....   case valueN:     doSomethingN();     break;   default:     doSomethingElse();     }

The switch statement works like this: The value of the expression is compared with each of the literal values in the case statements. If a match is found, the code sequence following that case statement is executed. If none of the constants matches the value of the expression, then the default statement is executed. However, the default statement is optional. If no case matches and no default is present, then no further action is taken. The break statement is used inside the switch to terminate a statement sequence. When a break statement is encountered, execution branches to the first line of code that follows the entire switch statement. This has the effect of “jumping out” of the switch.

2- Looping Statements:

           Looping statements or Iteration statements enable program execution to repeat one or more statements (that is,iteration statements form loops).

a: for loop:

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

The for loop operates as follows. When the loop first starts, the initialization portion of the loop is executed. Generally, this is an expression that sets the value of the loop control variable, which acts as a counter that controls the loop. It is important to understand that the initialization expression is only executed once. Next, condition is evaluated. This must be a Boolean expression. It usually tests the loop control variable against a target value. If this expression is true, then the body of the loop is executed. If it is false, the loop terminates. Next, the iteration portion of the loop is executed. This is usually an expression that increments or decrements the loop control variable. The loop then iterates, first evaluating the conditional expression, then executing the body of the loop, and then executing the iteration expression with each pass. This process repeats until the controlling expression is false.

b: do-while

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

Each iteration of the do-while loop first executes the body of the loop and then evaluates the conditional expression. If this expression is true, the loop will repeat. Otherwise, the loop terminates. As with all of Java’s loops, condition must be a Boolean expression

c: while

The while loop is Java’s most fundamental looping statement. It repeats a statement or block while its controlling expression is true. Here is its general form:

while(condition)  { // body of loop }

The condition can be any Boolean expression. The body of the loop will be executed as long as the conditional expression is true. When condition becomes false, control passes to the next line of code immediately following the loop. The curly braces are unnecessary if only a single statement is being repeated.

3- Branching Statements:

            Branching statements allow your program to execute in a nonlinear fashion. Break, jump and goto are the branching statements used in java.