Difference between new Test() and new Test() { }

Question

What is the difference between these two ways of instantiating new objects of a class as follows:

Test t1=new Test(); Test t2=new Test(){ }; 

When I tried the following code, I could see that both objects could access the method foo(), but t2 cannot access the variable x (variable x cannot be resolved):

public class Test {      int x=0;     public void foo(){ }      public static void main (String args[])     {         Test t1=new Test();         Test t2=new Test(){ };         t1.x=10;         t2.x=20;         t1.foo();         t2.foo();         System.out.println(t1.x+" "t2.x);     } } 

Answer 1

Test t2=new Test(); will create the object of Test class.

But Test t2=new Test(){ }; will create a object of subclass of test (i.e. anonymous inner class in this case).

you can provide implementation for any method over there like

Test t2=new Test(){  public void foo(){ System.out.println("This is foo");} }; 

so that when foo() method called from object t2 it will print This is foo.

Addition

Compile time error in your code is due to missing concatination operator

System.out.println(t1.x+" "+t2.x);                           ### 

Answer 2

The runtime type of both the references would be different. Try:

System.out.println(t1.getClass());  // class Test System.out.println(t2.getClass());  // class Test$1 

You will see different output. Reason being, the new Test() { } expression creates instance of an anonymous subclass of Test. So, Test$1 is a subclass of Test.

Now, the reason you're getting that error is, you're missing a + sign:

System.out.println(t1.x + " " + t2.x);                               ^ 

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