Java puzzle

package com.company;

class X1 {
    private final int x1 = 41;
    private X1 X1;
    public X1(X1 x1) { X1 = x1; }
    void print() {
        System.out.println(x1);
    }
}

class X2 {
    private final int x2 = 42;
    private X2 X2;
    public X2(X2 x2) { X2 = x2; }
    void print() {
        if (!X2.equals(this)) System.out.println(x2);
    }
}

class X3 {
    private final int x3 = 43;
    private X3 X3;
    void X3(X3 x3) { X3 = x3; }
    void print() {
        if (X3.equals(this)) System.out.println(x3);
    }
}

public class Main {
    public static void main(String[] args) {
        // your code goes here
        // print x1, x2 and x3 by invoking class print()
    }
}