what does this() mean in Java

Question

what does this() mean in Java?

It looks it is only valid when put

this();

in the class variable area.

Any one has idea about this?

Thanks.

Answer 1

It means you are calling the default constructor from another constructor. It has to be the first statement and you cannot use super() if you have. It is fairly rare to see it used.

Answer 2

It's a call to the no-argument constructor, which you can call as the first statement in another constructor to avoid duplicating code.

public class Test {

        public Test() {
        }

        public Test(int i) {
          this();
          // Do something with i
        }

}

Answer 3

It means "call constructor which is without arguments". Example:

public class X {
    public X() {
        // Something.
    }
    public X(int a) {
        this();   // X() will be called.
        // Something other.
    }
}

Answer 4

Calling this() wil call the constructor of the class with no arguments.

You would use it like this:

public MyObj() { this.name = "Me!"; }
public MyObj(int age) { this(); this.age = age; }

Answer 5

It is a call to a constructor of the containing class. See: http://download.oracle.com/javase/tutorial/java/javaOO/thiskey.html

Answer 6

See the example here: http://leepoint.net/notes-java/oop/constructors/constructor.html

You can call the constructor explicitly with this()

Answer 7

a class calling its own default constructor. It's more common to see it with arguments.