• The role of decision making statements in programming
• Use of if and switch statements
• Nested if statements

if statement
Within an “if” statement, first of all the given condition is checked. If it is true, the underlying statement is executed once. If it is false, program control is switched to the next statement.

Syntax

if(Boolean expression) {
        statement / block;
}

Example

        int i = 10;
if (i < 10 ) {
        System.out.println(“i is less than 10”);
} 

if / else statement
In the case of if/else statements, when the if statement becomes false, control of the program shifts to the else block.

Syntax

if (Boolean expression) {
        statement / block;
}
else {
        statement / block;
}

Example 1

        int i  = 11;
if ( i < 10 ) {
        System.out.println(“i is less than 10”);
} else {
        System.out.println(“i is greater than 10”);
}

Example 2

        int i = 11;
if (i < 10) {
        System.out.println(“i is less than 10”);
}
else if (i > 11) {
        System.out.println(“i is less than 11”);
}
else if (i == 11) {
        System.out.println(“i is equal to 11”);
}
else {
        System.out.println(“Number is not found”);
}

Nested if

In nested if statements, we declare an if statement within the declaration of another if statement. This forms a block of if statements.

Syntax

If (Boolean expression) {
        If (Boolean expression) {
                Statement block;
        }
                statement;
        }
        else
                statement;  

Mode of Execution

With nested if statements, first of all the outer if statement is executed. If the outer if statement is true then control will be shifted to the second if. If the second if is true the statements within its scope will be executed. When all the statements are executed, then program will control will shifted back to the outer if and any remaining statements there will be executed.

Example

class NestedIf {
        public static void main(String args[]) {
                String name = “Pakistan”;            
                if (name == “Pakistan”) {
                if (name.length() < 5 ) {
                        System.out.println(name);
                }
                        System.out.println(“This is the nested if “);
                }
                else
                System.out.println(“Your string is more than five letters”);
        }
}

The Switch Statement

The switch statement is similar to the if statement, except that it allows many values of any expression to be checked in a single statement. A switch statement can be implemented as a series of if-else statement.

First the case variable is checked. Then program execution transfers to the first statement identified by the case value that matches the result of the expression. The expression must be an integer or a character. It cannot evaluate to a Boolean or floating-point value.

Syntax

Switch (variable) {
        case value 1;
                statement-list1;
                break;

        case value 2;
                statement-list2;
                break;

        case value 3;    
                statement-list3;
                break;

        default;
                statement-list3;
                break;
}

Example

class SwitchEx {
        public static void main (String args[]) {
                int a = 15;
                switch (a) {
                case 1;
                        System.out.println(“My color is green”);
                        break;
                case 5;
                        System.out.println(“My color is blue”);
                        break;
                case 10;
                        System.out.println(“My color is yellow”);
                        break;
                default;
                        System.out.println(“My color is red”);
                        break;
                }
        }
}