Java:矩形类的Undo和Redo方法

Question

我有一个自定义矩形类：

public class Rectangle () {
private int height, width, x, y;
private Color color;

public Rectangle () {
this.height = null;
this.width = null;
this.x = null;
this.y = null;
this.color = null;
}

public void setHeight(int h) { this.height = h; }
public void setWidth(int w) { this.width = w; }

public void setX(int x) { this.x = x; }

public void setY(int y) { this.y = y; }

public void setColor(Color c) { this.color = c; }
public int getWidth() { return this.width; }

public int getHeight() { return this.height; }
public int getX() { return this.x; }

public int getY() { return this.y; }

public Color getColor() { return this.color; }

public void undo() {   }
public void redo() {   }
}

我该如何为这个类实现undo和redo函数，使它能够在用户不提及上次使用的方法的情况下将矩形恢复到以前的状态。我对使用堆栈有一个模糊的想法，但我一直纠结于如何实际编码它。我的第二个问题是，我不确定我的构造函数是否正确，我在不提供任何参数的情况下将所有内容初始化为null，因为我希望人们改为使用getter/setter。请帮忙。

Answer 1

您可以保存数组中的状态并从中恢复矩形

public class Rectangle () {

private states: List<Rectangle> = new ArrayList(); // we save the state of rectangle on every update to any property
private int stateIndex = 0; // this is the index of the state which is active on this rectangle

private int height, width, x, y;
private Color color;

public Rectangle () {
this.height = null;
this.width = null;
this.x = null;
this.y = null;
this.color = null;
}

public void setHeight(int h) { 
this.stateIndex = states.size() + 1; // we ll increase one in state index as new state is added to the states
this.height = h; 
this.states.add(this); // add the state after you set the value of any property
}

public void undo() { 
if(this.stateIndex > 0){ // only undo when there is state available before the current state
this.stateIndex--; // reduce the current index by one
this.height = this.states.get(stateIndex).height; // set the properties from state
...
}
}

public void redo() {    
if(this.stateIndex < states.size()){ // can go more the available states in cache
this.stateIndex++; // increase the current state index
this.height = this.states.get(stateIndex).height; // update the values of the properties
...
}
}
}