this & super

this and super are two reference keywords in Java. this refers to the current object — the instance whose method or constructor is currently running. super refers to the parent class of the current object. Both show up constantly in constructors and inheritance-related code.

this — Referring to the Current Object

The most common use of this is disambiguating a field from a parameter that share the same name — exactly the situation we saw on the Constructors page:

public class Book {
  String title;

  Book(String title) {
    this.title = title; // this.title is the field, title is the parameter
  }
}

Without this, writing title = title; would just assign the parameter to itself and leave the field untouched. this.title makes clear you mean the field that belongs to the object.

Calling Another Constructor with this(...)

this(...), used as the first line of a constructor, calls another constructor in the same class. It's a handy way to avoid repeating setup logic across overloaded constructors:

public class Book {
  String title;
  int pages;

  Book(String title) {
    this(title, 0); // delegates to the constructor below
  }

  Book(String title, int pages) {
    this.title = title;
    this.pages = pages;
  }
}

super — Referring to the Parent Class

Recall the Inheritance page, where a subclass extends a parent class. super lets the subclass reach back into that parent — to call an overridden method's original version, or to run the parent's constructor.

public class Animal {
  String name;

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

  void makeSound() {
    System.out.println("Some generic animal sound");
  }
}

public class Dog extends Animal {
  Dog(String name) {
    super(name); // calls Animal's constructor
  }

  void makeSound() {
    super.makeSound(); // runs Animal's version first
    System.out.println(name + " barks");
  }
}

super(name) forwards the constructor argument up to Animal's constructor. super.makeSound() calls the parent's original overridden method, before Dog adds its own behavior on top.

this vs super — Side by Side

	this	super
Refers to	The current object	The parent class of the current object
Field/method access	this.field, this.method()	super.field, super.method()
Constructor call	this(...) — another constructor in the same class	super(...) — the parent class's constructor
Typical purpose	Disambiguate fields from parameters; avoid duplicate constructor logic	Reuse or extend parent behavior; initialize inherited state
Placement rule	If used to call a constructor, must be the first statement	If used to call a constructor, must be the first statement