What is the meaning of this keyword in Java

Question

Normally, I use this in constructors only.

I understand that it is used to identify the parameter variable (by using this.something), if it have a same name with a global variable.

However, I don't know that what the real meaning of this is in Java and what will happen if I use this without dot (.).

Answer 1

public class MyThisTest {
  private int a;

  public MyThisTest() {
    this(42); // calls the other constructor
  }

  public MyThisTest(int a) {
    this.a = a; // assigns the value of the parameter a to the field of the same name
  }

  public void frobnicate() {
    int a = 1;

    System.out.println(a); // refers to the local variable a
    System.out.println(this.a); // refers to the field a
    System.out.println(this); // refers to this entire object
  }

  public String toString() {
    return "MyThisTest a=" + a; // refers to the field a
  }
}

Then calling frobnicate() on new MyThisTest() will print

1
42
MyThisTest a=42

So effectively you use it for multiple things:

• clarify that you are talking about a field, when there's also something else with the same name as a field
• refer to the current object as a whole
• invoke other constructors of the current class in your constructor