📓3.9: this Keyword

Table of Contents

📖 This page is a condensed version of CSAwesome Topic 3.9

In Java, the keyword this refers to the current object — the one whose method or constructor is being executed.

Uses of this

1. Referencing Instance Variables

When a method parameter has the same name as an instance variable, this can be used to distinguish between them.

public class Dog {
    private String name;

    public Dog(String name) {
        this.name = name; // 'this.name' refers to the instance variable
    }
}

2. Calling Another Constructor

this() can be used inside a constructor to call another constructor in the same class.

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

    public Dog(String name) {
        this(name, 0); // calls the two-parameter constructor
    }

    public Dog(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

3. Passing the Current Object

You can pass this as an argument to another method or constructor.

public class Dog {
    public void register() {
        Registry.addDog(this); // passes the current Dog object
    }
}

Why this Is Useful

  • Clarifies references when variable names conflict.
  • Allows constructor chaining.
  • Makes it easier to pass the current object to other methods or classes.

Summary

  • this refers to the current object.
  • Use it to distinguish variables, call other constructors, or pass the object.
  • Improves clarity and flexibility in object-oriented code.

AP Practice

Question</summary>

In the constructor public Dog(String name) { this.name = name; }, what does this.name refer to?

  • A. The method parameter name
  • B. The instance variable name ✅
  • C. A local variable name
  • D. A static variable name

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Acknowledgement

Content on this page is adapted from Runestone Academy - Barb Ericson, Beryl Hoffman, Peter Seibel.