Java Keywords

Categories of Keywords

Grouping keywords by purpose makes them far easier to remember than treating them as one flat list.

• Data type keywords: byte, short, int, long, float, double, char, boolean, void.
• Access modifiers: public, private, protected.
• Class/interface related: class, interface, extends, implements, abstract, final, static, package, import, new, this, super, instanceof.
• Control flow: if, else, switch, case, default, for, while, do, break, continue, return.
• Exception handling: try, catch, finally, throw, throws.
• Other: synchronized, volatile, transient, native, strictfp, assert, enum, const (reserved but unused), goto (reserved but unused).

Reserved Literals and Contextual Keywords

true, false, and null are technically reserved literals, not keywords, but they behave the same way: you cannot use them as identifiers. Newer Java versions also introduced "contextual keywords" like var, record, sealed, and yield, which are only treated specially in certain positions — you can still use words like "record" as a variable name in older code, unlike true keywords.

Example

public abstract class Vehicle {
    protected final String name;

    public Vehicle(String name) {
        this.name = name;
    }

    public abstract void move();
}

class Car extends Vehicle {
    public Car(String name) {
        super(name);
    }

    @Override
    public void move() {
        if (this.name != null) {
            System.out.println(this.name + " is moving");
        }
    }
}

(Compiles cleanly — demonstrates abstract, extends, final, protected, super, this, @Override together)

Exercise

This program fails to compile because three variables are named with reserved words. Rename them to sensible identifiers so that it compiles.

Expected output: Order 42 total 199.5 new=true

public class OrderSummary {
    public static void main(String[] args) {
        int case = 42;
        double double = 199.5;
        boolean new = true;
        System.out.println("Order " + case + " total " + double + " new=" + new);
    }
}

public class OrderSummary {
    public static void main(String[] args) {
        int orderNumber = 42;
        double total = 199.5;
        boolean isNew = true;
        System.out.println("Order " + orderNumber + " total " + total + " new=" + isNew);
    }
}

Quick quiz

Interview questions

Go deeper

• final vs finally vs finalize