Java if, else and else if

Programs must take decisions. The if statement runs a block of code only when a condition is true.

if

public class Main {
    public static void main(String[] args) {
        int marks = 72;
        if (marks >= 40) {
            System.out.println("You passed");
        }
        System.out.println("End of program");
    }
}

if … else

public class Else {
    public static void main(String[] args) {
        int age = 16;
        if (age >= 18) {
            System.out.println("Adult");
        } else {
            System.out.println("Minor");
        }
    }
}

else if

Use else if to check many conditions. Java checks from the top and stops at the first true one.

public class Grade {
    public static void main(String[] args) {
        int marks = 76;
        if (marks >= 90) {
            System.out.println("Grade A+");
        } else if (marks >= 75) {
            System.out.println("Grade A");
        } else if (marks >= 60) {
            System.out.println("Grade B");
        } else if (marks >= 40) {
            System.out.println("Grade C");
        } else {
            System.out.println("Fail");
        }
    }
}

Nested if

public class Nested {
    public static void main(String[] args) {
        int age = 25;
        boolean hasLicense = true;
        if (age >= 18) {
            if (hasLicense) {
                System.out.println("You can drive");
            } else {
                System.out.println("Get a license first");
            }
        }
    }
}

You can write this in a cleaner way with &&: if (age >= 18 && hasLicense).

Comparing text in conditions

public class Text {
    public static void main(String[] args) {
        String role = "admin";
        if (role.equals("admin")) {          // not role == "admin"
            System.out.println("Welcome, admin");
        }
    }
}

The ternary operator

public class Ternary {
    public static void main(String[] args) {
        int n = 7;
        String type = (n % 2 == 0) ? "even" : "odd";
        System.out.println(n + " is " + type);
    }
}

Common mistakes

• Using = (assignment) instead of == (comparison). Java stops this for int values: if (x = 5) does not compile.
• A semicolon after the condition: if (x > 5); makes an empty if.
• Leaving out the braces, then adding a second line which is not inside the if.

public class Mistake {
    public static void main(String[] args) {
        int x = 3;
        if (x = 5) {
            System.out.println("five");
        }
    }
}

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