How is the 'this' variable in Java actually set to the current object?

Question

Consider:

class TestParent{
  public int i = 100;
  public void printName(){
    System.err.println(this); //{TestChild@428} according to the Debugger.
    Syste         


        

Answer 1

Adding some more info on top of @Tom Anderson answer, which explains hiding concept nicely.

I have added one more constructor in Child ( TestChild) which prints values of i in both parent and child.

If you want get value of i from child (TestChild), override the method in TestChild.

class TestParent{
  public int i = 100;
  public void printName(){
    System.err.println("TestParent:printName()");
    System.err.println(this); //{TestChild@SOME_NUM} according to the Debugger.
    System.err.println(this.i); //this.i is 100.
  }
}

class TestChild extends TestParent{
  public int i = 200;
  public TestChild(){
    System.out.println("TestChild.i and TestParent.i:"+this.i+":"+super.i);
  }
  public void printName(){
      //super.printName();
      System.err.println("TestChild:printName()");
      System.err.println(this); //{TestChild@SOME_NUM} according to the Debugger.
      System.err.println(this.i); //this.i is 200.
  }
}

public class ThisTest {
  public static void main(String[] args) {
    TestParent parent = new TestChild();
    parent.printName();
  }
}

Case 1: If I comment super.printName() call from child, Child version of TestChild.printName() prints the value of i in TestChild

Output:

TestChild.i and TestParent.i:200:100
TestChild:printName()
TestChild@43cda81e
200

Case 2: TestChild.printName() calls super.printName() as the first line in printName() method. In this case, i value from both parent and child are displayed in respective methods.

Output:

TestChild.i and TestParent.i:200:100
TestParent:printName()
TestChild@43cda81e
100
TestChild:printName()
TestChild@43cda81e
200