Java Control Flow Statements

Java Control statements control the order of execution in a java program, based on data values and conditional logic. There are three main categories of control flow statements;
Selection statements: if, if-else and switch. · Loop statements: while, do-while and for.

· Transfer statements: break, continue, return, try-catch-finally and assert.

We use control statements when we want to change the default sequential order of execution

Selection Statements

The If Statement

The if statement executes a block of code only if the specified expression is true. If the value is false, then the if block is skipped and execution continues with the rest of the program. You can either have a single statement or a block of code within an if statement. Note that the conditional expression must be a Boolean expression.

The simple if statement has the following syntax:

if ()

Below is an example that demonstrates conditional execution based on if statement condition.

public class IfStatementDemo {



	public static void main(String[] args) {

		int a = 10, b = 20;

		if (a > b)

			System.out.println(”a > b”);

		if (a <> a”);

	}

}

Output

b > a


The If-else Statement

The if/else statement is an extension of the if statement. If the statements in the if statement fails, the statements in the else block are executed. You can either have a single statement or a block of code within if-else blocks. Note that the conditional expression must be a Boolean expression.

The if-else statement has the following syntax:

if ()

else

Below is an example that demonstrates conditional execution based on if else statement condition. 

public class IfElseStatementDemo {



	public static void main(String[] args) {

		int a = 10, b = 20;

		if (a > b) {

			System.out.println(”a > b”);

		} else {

			System.out.println(”b > a”);

		}

	}

}

Output

b > a


Switch Case Statement The switch case statement, also called a case statement is a multi-way branch with several choices. A switch is easier to implement than a series of if/else statements. The switch statement begins with a keyword, followed by an expression that equates to a no long integral value. Following the controlling expression is a code block that contains zero or more labeled cases. Each label must equate to an integer constant and each must be unique. When the switch statement executes, it compares the value of the controlling expression to the values of each case label. The program will select the value of the case label that equals the value of the controlling expression and branch down that path to the end of the code block. If none of the case label values match, then none of the codes within the switch statement code block will be executed. Java includes a default label to use in cases where there are no matches. We can have a nested switch within a case block of an outer switch.

Its general form is as follows:

switch () {
case label1: 1>
case label2: 2>
…
case labeln: n>
default:
} // end switch

When executing a switch statement, the program falls through to the next case. Therefore, if you want to exit in the middle of the switch statement code block, you must insert a break statement, which causes the program to continue executing after the current code block.

Below is a java example that demonstrates conditional execution based on nested if else statement condition to find the greatest of 3 numbers.

public class SwitchCaseStatementDemo {



	public static void main(String[] args) {

		int a = 10, b = 20, c = 30;

		int status = -1;

		if (a > b && a > c) {

			status = 1;

		} else if (b > c) {

			status = 2;

		} else {

			status = 3;

		}

		switch (status) {

		case 1:

			System.out.println(”a is the greatest”);

			break;

		case 2:

			System.out.println(”b is the greatest”);

			break;

		case 3:

			System.out.println(”c is the greatest”);

			break;

		default:

			System.out.println(”Cannot be determined”);

		}

	}

}

Output

c is the greatest