如何在不访问私有变量的情况下创建实例的副本

Question

Im having a bit of a problem. Let me show you the code first:

public class Direction {
    private CircularList xSpeed, zSpeed;
    private int[] dirSquare = {-1, 0, 1, 0};

public Direction(int xSpeed, int zSpeed){
    this.xSpeed = new CircularList(dirSquare, xSpeed);
    this.zSpeed = new CircularList(dirSquare, zSpeed);
}
public Direction(Point dirs){
    this(dirs.x, dirs.y);
}
public void shiftLeft(){
    xSpeed.shiftLeft();
    zSpeed.shiftRight();
}
public void shiftRight(){
    xSpeed.shiftRight();
    zSpeed.shiftLeft();
}
public int getXSpeed(){
    return this.xSpeed.currentValue();
}
public int getZSpeed(){
    return this.zSpeed.currentValue();
}
}

Now lets say i have an instance of Direction:

Direction dir = new Direction(0, 0);

As you can see in the code of Direction, the arguments fed to the constructor, are passed directly to some other class. One cannot be sure if they stay the same because methods shiftRight() and shiftLeft could have been called, which changes thos numbers.

My question is, how do i create a completely new instance of Direction, that is basically copy(not by reference) of dir?

The only way i see it, is to create public methods in both CircularList and Direction that return the variables needed to create a copy of the instance, but this solution seems really dirty since those numbers are not supposed to be touched after beeing fed to the constructor, and therefore they are private.

EDIT1:

CircularList is a class that is a looped around version of ArrayList. You can see that i feed it an array called dirSquare and then a number. The number is an index in that array. So if the number i feed it is for example 3, it will be the last element in dirSquare, which has value of 0. When i use shiftRight and shiftLeft, the index gets incremented/decremented and if i increment pass the size of the last element of the array, it loops around and starts with 0th elemnt. The same thing happens if i go pass 0 on the other side. Thats why its called Circular list. I cant use getXSpeed/getZSpeed because they return the value of the array. I need the index, which is strictly an implementation variable.

Answer 1

Why not add another constructor taking a Direction parameter. Something like:

public Direction(Direction source) {
    this(source.xSpeed, source.ZSpeed);
}

Answer 2

A common way to go about this, is to create a copy constructor. An example can be found here

Another solution would be to implement the Cloneable interface, but most developers recommend against it, including Joshua Bloch in Effective Java , calling Java's clone " deeply broken ".

Answer 3

I'd add a private/protected constructor without arguments, so you can initialize each member with its own copy (with your constructor it seems you'll have a reference inside your CircularLists, so you need to inizialize them manually inside clone method).

public Direction() {};

public Direction Clone() {
    Direction dir = new Direction();
    dir.diSquare=this.dirSquare;

    for each elem in xSpeed
        dir.xSpeed.Add(elem)

    for each elem in zSpeed
        dir.zSpeed.Add(elem)

    return dir;
}