Conditional Control Statements

if, else if, else

• The condition must be boolean — you cannot write if (x) for an int like C/C++.
• Braces are optional for one statement but you should always use them to avoid dangling-else bugs.

public class GradeIf {
    public static void main(String[] args) {
        int marks = 76;
        if (marks >= 90) {
            System.out.println("A");
        } else if (marks >= 75) {
            System.out.println("B");
        } else {
            System.out.println("C or below");
        }
    }
}

Classic switch (statement)

• Supported selector types: byte, short, char, int and their wrappers, String (Java 7+), and enums.
• long, float, double, and boolean cannot be switch selectors.
• Without break, execution falls through to the next case — usually a bug, sometimes intentional.

Switch expressions (Java 14+)

• Arrow cases (case 1 ->) do not fall through. A switch can produce a value.
• yield is used in a block case to produce the value. default is required when the switch is used as an expression (unless the enum is exhaustive).

Nested decisions and pattern matching

• Deeply nested if is hard to test — extract methods or use a switch/table.
• Java 16+ if (obj instanceof String s) binds s if the test succeeds (pattern matching for instanceof).
• Java 17 preview/21+ expands switch pattern matching; interviews for Java 17 still focus on classic + arrow switch.

Switch expression (Java 14+)

public class DayType {
    public static void main(String[] args) {
        String day = "SAT";
        String kind = switch (day) {
            case "SAT", "SUN" -> "weekend";
            case "MON", "TUE", "WED", "THU", "FRI" -> "weekday";
            default -> "unknown";
        };
        System.out.println(kind);
    }
}

Classic switch with break

public class ClassicSwitch {
    public static void main(String[] args) {
        int n = 2;
        switch (n) {
            case 1:
                System.out.println("one");
                break;
            case 2:
                System.out.println("two");
                break;
            default:
                System.out.println("other");
        }
    }
}