“ this.getClass（）。getSuperclass（）”的意外输出

Question

Consider below two cases

Case I

I have a simple Java class which has a no-arguments constructor. Below is the code

public class TestClassOne {

      public TestClassOne() {
           System.out.println("Parent class of TestClassOne is :" + this.getClass().getSuperclass());
    }
}

Object is the super class of all Java classes. So when I am creating an object of TestClassOne in my main method and run it, it is giving me the desire output which is

Parent class of TestClassOne is :class java.lang.Object

Case II

Now I have another class, named as TestClassTwo which extends TestClassOne. Below is the code

public class TestClassTwo extends TestClassOne {
}

Now when I am creating object of TestClassTwo in my main method and run it, TestClassOne's no-arguments constructor is also getting called implicitly as TestClassOne is super class of TestClassTwo and prints the output in the console. I was expecting the output will be same with the case I. But it is not. The output is

Parent class of TestClassOne is :class org.test.TestClassOne

Why not the above output is same with Case I ?

Could someone explain me why the outputs are different in Case I and Case II?

Answer 1

You're calling getClass() on this . The output is different because:

• In case 1, this refers to an instance of TestClassOne .
• In case 2, this refers to an instance of TestClassTwo .

Answer 2

Simple answer: Because this is the superclass.

public class TestClassOne {
    public TestClassOne() {
        System.out.println("Parent class of TestClassOne is :" + this.getClass().getSuperclass());
    }
}

This class extends java.lang.Object (even if it is not explicitly named).

So this references to an object of the class TestClassOne and the superclass is java.lang.Object .

public class TestClassTwo extends TestClassOne {
}

This class extends TestClassOne .

So this references to an object of the class TestClassTwo and the superclass is TestClassOne .

For this always the current object is used and never the class where it is defined.