Java If, Else and Switch

Programs need to make decisions: is the password correct? Is the cart empty? Did the student pass? Conditions let your code take different paths.

if and else#

public class Grades {
    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");
        }
    }
}

Output: Grade A. Java checks from top to bottom and runs only the first block whose condition is true.

• The condition must be a boolean. if (marks) is an error in Java (unlike JavaScript or Python).
• Braces are optional for a single statement, but always use them. It prevents bugs when you add a second line later.

Combining conditions#

int age = 19;
boolean hasTicket = true;
boolean vip = false;

if ((age >= 18 && hasTicket) || vip) {
    System.out.println("Welcome to the concert!");
}

Nested if#

boolean loggedIn = true;
String role = "admin";

if (loggedIn) {
    if ("admin".equals(role)) {
        System.out.println("Open admin dashboard");
    } else {
        System.out.println("Open user dashboard");
    }
} else {
    System.out.println("Please sign in");
}

Deep nesting gets hard to read. A cleaner style is the guard clause: handle the “exit early” cases first.

static String dashboard(boolean loggedIn, String role) {
    if (!loggedIn) return "Please sign in";
    if ("admin".equals(role)) return "Admin dashboard";
    return "User dashboard";
}

The classic switch statement#

When comparing one value against many fixed options, switch is cleaner than a long else if chain:

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("Another day");
}

**Don’t forget break!** Without it, Java “falls through” and runs the next cases too:

int n = 1;
switch (n) {
    case 1: System.out.println("one");
    case 2: System.out.println("two");      // also printed!
    default: System.out.println("many");    // also printed!
}

switch works with int, char, String, enums (and their wrapper types).

The modern switch expression (Java 14+)#

Arrows -> never fall through, and the switch can return a value:

public class Seasons {
    public static void main(String[] args) {
        String month = "OCT";
        String season = switch (month) {
            case "DEC", "JAN", "FEB" -> "Winter";
            case "MAR", "APR", "MAY" -> "Summer";
            case "JUN", "JUL", "AUG", "SEP" -> "Monsoon";
            case "OCT", "NOV" -> "Post-monsoon";
            default -> "Unknown";
        };
        System.out.println(season);    // Post-monsoon
    }
}

• Several labels share one case: case "DEC", "JAN", "FEB".
• No break needed.
• Need several statements? Use a block and yield:

int fee = switch (plan) {
    case "student" -> 0;
    case "pro" -> {
        int base = 499;
        yield base - 50;     // yield returns the value from a block
    }
    default -> 999;
};

Pattern matching for switch (Java 21)#

Java 21 can switch on the type of an object:

static String describe(Object o) {
    return switch (o) {
        case Integer i when i > 100 -> "big number " + i;
        case Integer i -> "number " + i;
        case String s -> "text of length " + s.length();
        case null -> "nothing";
        default -> "something else";
    };
}

You’ll use this more after the OOP course.

Common mistakes#

• if (x = 5) instead of if (x == 5).
• Comparing Strings with == in conditions: use .equals().
• A semicolon after the condition: if (ok); { ... } makes the block run always!
• Forgetting break in classic switch.
• Order of else if matters: put the most specific conditions first (>= 90 before >= 75).

Exercise#

1. Read a number and print whether it’s positive, negative or zero, and whether it’s even or odd.
2. Read three numbers and print the largest using only if/else.
3. Electricity bill: first 100 units ₹5 each, next 100 units ₹7, above 200 units ₹10. Calculate the bill for any number of units.
4. Use a switch expression to convert a number 1-7 into a day name.

Hint for 3

For 250 units: 100 × 5 + 100 × 7 + 50 × 10. Use Math.min or an if/else chain to split units into slabs.

Interview corner#

• What types can switch work on? byte, short, char, int, their wrappers, String, enums, and (Java 21) any type with pattern matching.
• What is fall-through? In classic switch, without break execution continues into the next case.
• Switch statement vs expression? A statement performs actions; an expression produces a value (with -> or yield).

Summary#

• if / else if / else picks the first true branch; conditions must be boolean.
• Use guard clauses to avoid deep nesting.
• Classic switch needs break; the modern arrow switch returns values and never falls through.

Next: loops, to repeat work without repeating code.