this and super Keywords

Syntax

this.field = value;\nsuper.method();

Examples

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;  // this.name is the field, name is the parameter
        this.age = age;
    }
}

public class Box {
    private int width, height;

    public Box(int size) {
        this(size, size);  // calls the two-argument constructor below
    }

    public Box(int width, int height) {
        this.width = width;
        this.height = height;
    }
}

Box square = new Box(5);       // 5x5
Box rect = new Box(4, 8);       // 4x8

class Animal {
    protected String name;

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

class Dog extends Animal {
    private String breed;

    public Dog(String name, String breed) {
        super(name);  // must be the first line in the subclass constructor
        this.breed = breed;
    }
}

Dog dog = new Dog("Rex", "Labrador");

class Vehicle {
    public String describe() {
        return "A vehicle";
    }
}

class Car extends Vehicle {
    @Override
    public String describe() {
        return super.describe() + " that is a car";  // extends, doesn't replace
    }
}

Car car = new Car();
System.out.println(car.describe());  // A vehicle that is a car

Best practices

• Use this. to disambiguate between a field and a parameter of the same name, a very common and idiomatic pattern in constructors
• A call to super(...) must be the very first statement in a subclass constructor - Java enforces this at compile time
• Use super.methodName() when a subclass override needs to extend the parent behavior rather than completely replace it
• You don't need this. for every field reference - use it specifically when there's a naming conflict or for clarity in constructors

At a glance

Purpose

General-purpose application development

File extension

.java

Runs in

Java Virtual Machine

Usually used with

JDK and Java libraries

Specifications & further reading

• Java Language Specification

Related Java documentation