Khalid Ahmad Khattak

Lesson 7 – Conditions

Conditions allow a program to make decisions. Java provides three main structures:

• if statements
• if–else statements
• else if chains
• switch statements

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1. The if Statement

The if statement runs a block of code only when a condition is true.

Example 1 – Full Program

public class Main {
    public static void main(String[] args) {
        int age = 20;

        if (age >= 18) {
            System.out.println("You are an adult.");
        }
    }
}
        

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2. The if–else Statement

Use when you want one of two actions to run.

Example 2 – Full Program

public class Main {
    public static void main(String[] args) {
        int number = 5;

        if (number % 2 == 0) {
            System.out.println("Even number");
        } else {
            System.out.println("Odd number");
        }
    }
}
        

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3. The else if Chain

Use when testing several conditions.

Example 3 – Full Program

public class Main {
    public static void main(String[] args) {
        int marks = 85;

        if (marks >= 90) {
            System.out.println("Grade A");
        } else if (marks >= 80) {
            System.out.println("Grade B");
        } else if (marks >= 70) {
            System.out.println("Grade C");
        } else {
            System.out.println("Fail");
        }
    }
}
        

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4. Nested if Statements

You can put an if inside another if.

Example 4 – Full Program

public class Main {
    public static void main(String[] args) {
        int age = 16;
        boolean hasPermission = true;

        if (age >= 16) {
            if (hasPermission) {
                System.out.println("You can drive.");
            } else {
                System.out.println("You need permission to drive.");
            }
        } else {
            System.out.println("You are too young.");
        }
    }
}
        

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5. Real-Life Example – Shopping Discount

Example 5 – Full Program

public class Main {
    public static void main(String[] args) {
        double amount = 250;

        if (amount >= 500) {
            System.out.println("Discount: 20%");
        } else if (amount >= 300) {
            System.out.println("Discount: 10%");
        } else if (amount >= 100) {
            System.out.println("Discount: 5%");
        } else {
            System.out.println("No discount");
        }
    }
}
        

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6. The switch Statement

Use switch when checking one variable for many possible values.

Keyword	Meaning
switch	Begins the selection
case	One possible match
break	Stop and exit switch
default	If no case matches

Example 6 – Full Program

public class Main {
    public static void main(String[] args) {
        int day = 3;

        switch (day) {
            case 1:
                System.out.println("Monday");
                break;

            case 2:
                System.out.println("Tuesday");
                break;

            case 3:
                System.out.println("Wednesday");
                break;

            default:
                System.out.println("Invalid day");
        }
    }
}
        

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7. Switch with Strings

Java also allows String in switch-cases.

Example 7 – Full Program

public class Main {
    public static void main(String[] args) {
        String fruit = "apple";

        switch (fruit) {
            case "apple":
                System.out.println("You chose apple");
                break;

            case "banana":
                System.out.println("You chose banana");
                break;

            default:
                System.out.println("Unknown fruit");
        }
    }
}
        

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8. Real-Life Example – Simple Calculator (switch)

Example 8 – Full Program

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter first number: ");
        double a = input.nextDouble();

        System.out.print("Enter operator (+, -, *, /): ");
        char op = input.next().charAt(0);

        System.out.print("Enter second number: ");
        double b = input.nextDouble();

        switch (op) {
            case '+':
                System.out.println("Result: " + (a + b));
                break;

            case '-':
                System.out.println("Result: " + (a - b));
                break;

            case '*':
                System.out.println("Result: " + (a * b));
                break;

            case '/':
                System.out.println("Result: " + (a / b));
                break;

            default:
                System.out.println("Invalid operator");
        }
    }
}
        

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Summary

• if and else are used for decision making
• else if checks multiple conditions
• switch is useful for many fixed options
• Always use break in switch cases

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