JAVA it does not clone well

Question

I tried to clone the object of Test2 using the "KUROONN" method. I expected the second line of the output to read [0,0], but the real result shows [33,4]. I have no idea why this happens, so can anyone explain this?

import java.util.ArrayList;

class Test {
    public static ArrayList<Integer> T=new ArrayList<Integer>(); 
}

class Test2 {
    int Test2Int;
    ArrayList<Integer> Test2List;
    public Test2(int K,ArrayList<Integer> A) {
        this.Test2Int=K;
        this.Test2List=A;
    }
    public Test2 KUROONN() { //broken clone
        Test2 b=new Test2(0,Test.T);
        b.Test2Int=this.Test2Int;
        System.out.println(b.Test2List);
        for(int i=0;i<this.Test2List.size();i++) {
            b.Test2List.add(this.Test2List.get(i));
        }
        return b;
    }

}

public class testtube001a {
    public static void main (String args[]){
        ArrayList<Integer> n =new ArrayList<Integer>();
        n.add(33);
        n.add(4);
        ArrayList<Integer> m =new ArrayList<Integer>();
        m.add(114);
        m.add(514);
        Test2 t2_1=new Test2(72,n);
        Test2 t2_2=new Test2(1919,m);
        t2_1.KUROONN();
        t2_2.KUROONN();
    }
}

The output of the program is:

[]
[33, 4]

Answer 1

You have declared the T field as:

public static ArrayList<Integer> T=new ArrayList<Integer>(); 

The word static means the variable is shared between all instances. So when the code

Test2 b=new Test2(0,Test.T);

is executed, it will create an instance of Test2 that references that shared variable. The first time it will be empty, and your print will result in []. The second time it will reference the same list in which the first call added the values 33 and 4, hence it will print [33, 4]. After that, the values 114 and 514 will also be added to the same list.