Java Lesson — if, else, ternary operator, and switch

Why decision making matters

Real programs do not just run line by line without thinking. They must make decisions. For example:

• If marks are above 40, print pass.
• If age is less than 18, do not allow voting.
• If the day is Monday, print the Monday schedule.
• If the password is correct, allow login.

Decision statements make your programs intelligent and responsive.

Level 0 — The if statement

The simplest decision statement in Java is if. It checks a condition. If the condition is true, the code inside the block runs.

if (condition) {
    // code to run if condition is true
}

Example

int age = 20;

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

Since age >= 18 is true, the message is printed.

Another example

int marks = 75;

if (marks >= 40) {
    System.out.println("Pass");
}

Level 1 — The if-else statement

Sometimes you want one action when the condition is true and another action when it is false. That is where else is used.

if (condition) {
    // code if true
} else {
    // code if false
}

Example

int marks = 32;

if (marks >= 40) {
    System.out.println("Pass");
} else {
    System.out.println("Fail");
}

Since the condition is false here, the program prints Fail.

Level 2 — The else if ladder

When there are many possible conditions, you can use else if. Java checks each condition from top to bottom. As soon as one condition is true, that block runs and the rest are skipped.

if (condition1) {
    // block 1
} else if (condition2) {
    // block 2
} else if (condition3) {
    // block 3
} else {
    // default block
}

Example with grades

int marks = 84;

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");
}

Because 84 is not greater than or equal to 90 but is greater than or equal to 75, the program prints Grade A.

Level 3 — Nested if statements

A nested if statement means an if inside another if. Use this when a second decision depends on the first one.

int age = 20;
boolean hasId = true;

if (age >= 18) {
    if (hasId) {
        System.out.println("Entry allowed.");
    } else {
        System.out.println("Bring your ID.");
    }
} else {
    System.out.println("You are underage.");
}

Nested logic is powerful, but too much nesting can make code hard to read. Later in this lesson, we will see how to keep such code clean.

Conditions must be boolean

In Java, the condition inside if must be a boolean expression. That means it must evaluate to either true or false.

int x = 10;

if (x > 5) {
    System.out.println("x is greater than 5");
}

This is correct because x > 5 is a boolean expression.

int x = 10;

// This is wrong in Java
// if (x) {
//     System.out.println("Hello");
// }

Unlike some other languages, Java does not allow plain numbers as conditions.

Using relational and logical operators in if statements

Decision making becomes more useful when combined with relational operators like >, <, ==, and logical operators like &&, ||, and !.

int age = 22;
boolean hasTicket = true;

if (age >= 18 && hasTicket) {
    System.out.println("You may enter.");
} else {
    System.out.println("Entry not allowed.");
}

boolean isHoliday = false;
boolean isSunday = true;

if (isHoliday || isSunday) {
    System.out.println("No school today.");
}

Common mistakes in if and else

• Using = instead of == for comparison.
• Forgetting curly braces when multiple statements belong to the block.
• Writing overlapping conditions in the wrong order.
• Creating very deep nested code that becomes hard to understand.

Wrong order example

int marks = 95;

if (marks >= 40) {
    System.out.println("Pass");
} else if (marks >= 90) {
    System.out.println("Excellent");
}

This is wrong because any value above 90 is also above 40, so the first block runs and the second block is never reached.

Correct order example

int marks = 95;

if (marks >= 90) {
    System.out.println("Excellent");
} else if (marks >= 40) {
    System.out.println("Pass");
} else {
    System.out.println("Fail");
}

The ternary operator

The ternary operator is a short form of if-else. It is useful when you want to choose one of two values quickly.

condition ? valueIfTrue : valueIfFalse

Simple example

int age = 17;

String result = (age >= 18) ? "Adult" : "Minor";
System.out.println(result);

This means: if age >= 18 is true, use "Adult". Otherwise, use "Minor".

Equivalent if-else code

String result;

if (age >= 18) {
    result = "Adult";
} else {
    result = "Minor";
}

When to use ternary and when not to use it

Use the ternary operator when the logic is short and simple. Avoid it when the expression becomes long or confusing.

Good ternary use

int num = 8;
String type = (num % 2 == 0) ? "Even" : "Odd";
System.out.println(type);

Poor ternary use

String result = (marks >= 90) ? "A+" :
                (marks >= 75) ? "A" :
                (marks >= 60) ? "B" :
                (marks >= 40) ? "C" : "Fail";

This works, but it is harder to read. In such cases, an else if ladder is usually better.

The switch statement

Use switch when one variable or expression can have several fixed values, and you want different code for each value.

switch (expression) {
    case value1:
        // code
        break;
    case value2:
        // code
        break;
    default:
        // code
}

Example with day number

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;
    case 4:
        System.out.println("Thursday");
        break;
    case 5:
        System.out.println("Friday");
        break;
    case 6:
        System.out.println("Saturday");
        break;
    case 7:
        System.out.println("Sunday");
        break;
    default:
        System.out.println("Invalid day");
}

What break does in switch

The break statement stops the switch once a matching case has run. Without break, execution continues into the next cases. This is called fall-through.

Example without break

int day = 2;

switch (day) {
    case 1:
        System.out.println("Monday");
    case 2:
        System.out.println("Tuesday");
    case 3:
        System.out.println("Wednesday");
    default:
        System.out.println("Done");
}

Here, if day is 2, Java prints Tuesday, then Wednesday, then Done, because there are no breaks.

Intentional fall-through example

char grade = 'B';

switch (grade) {
    case 'A':
    case 'B':
    case 'C':
        System.out.println("Pass");
        break;
    case 'D':
    case 'F':
        System.out.println("Needs improvement");
        break;
    default:
        System.out.println("Unknown grade");
}

Here, fall-through is used on purpose to group cases together.

switch with strings

Java can also use strings in a switch statement.

String role = "admin";

switch (role) {
    case "admin":
        System.out.println("Full access");
        break;
    case "teacher":
        System.out.println("Teaching access");
        break;
    case "student":
        System.out.println("Learning access");
        break;
    default:
        System.out.println("Unknown role");
}

Modern switch expression

Modern Java also supports a cleaner switch style using arrows. This style is shorter and avoids many break-related mistakes.

int day = 5;

switch (day) {
    case 1 -> System.out.println("Monday");
    case 2 -> System.out.println("Tuesday");
    case 3 -> System.out.println("Wednesday");
    case 4 -> System.out.println("Thursday");
    case 5 -> System.out.println("Friday");
    case 6 -> System.out.println("Saturday");
    case 7 -> System.out.println("Sunday");
    default -> System.out.println("Invalid day");
}

Switch expression returning a value

int day = 6;

String type = switch (day) {
    case 1, 2, 3, 4, 5 -> "Weekday";
    case 6, 7 -> "Weekend";
    default -> "Invalid";
};

System.out.println(type);

if-else versus switch

Expert tips for cleaner decision-making code

• Put more specific conditions before more general ones.
• Avoid deeply nested code when a clearer structure is possible.
• Use ternary only for simple value selection.
• Use switch when testing one value against many fixed options.
• Name boolean variables clearly, like isLoggedIn or hasTicket.
• Keep blocks short and readable.
• When logic becomes complex, consider moving it into a separate method.

Complete beginner-to-advanced example

public class Main {
    public static void main(String[] args) {
        int marks = 82;
        int day = 6;
        boolean hasProject = true;

        // if-else-if ladder
        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");
        }

        // ternary operator
        String projectStatus = hasProject ? "Project submitted" : "Project missing";
        System.out.println(projectStatus);

        // switch expression
        String dayType = switch (day) {
            case 1, 2, 3, 4, 5 -> "Weekday";
            case 6, 7 -> "Weekend";
            default -> "Invalid";
        };

        System.out.println(dayType);

        // nested if
        if (marks >= 40) {
            if (hasProject) {
                System.out.println("Student passed and completed project.");
            } else {
                System.out.println("Student passed but project is missing.");
            }
        } else {
            System.out.println("Student failed.");
        }
    }
}

Assignments

Interactive MCQ Quiz

Choose one answer for each question and click Check Answers.

Quick revision

• if runs code only when the condition is true.
• if-else lets you choose between two paths.
• else if is used for multiple conditions.
• Ternary is a short form of simple if-else.
• switch is best when checking one value against many fixed cases.
• break prevents unwanted fall-through in traditional switch.
• Modern switch with arrows is cleaner and safer.