英文:
Java: Undo and Redo methods for a Rectangle class
问题
我有一个自定义的矩形（Rectangle）类：
public class Rectangle {
private int height, width, x, y;
private Color color;
public Rectangle() {
this.height = 0;
this.width = 0;
this.x = 0;
this.y = 0;
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() { }
}
如何在不要求用户提供上一步使用的方法的情况下，实现此类的撤销（undo）和重做（redo）功能，使得矩形能够回到之前的状态？我有一个模糊的想法，涉及使用栈（stack），但我在如何编写实际代码方面遇到了困难。我的第二个问题是，我不确定我的构造函数是否正确，我将所有变量初始化为 null，而没有提供任何参数，因为我希望用户使用 getters 和 setters 来设置值。请帮忙。
英文:
I have a custom Rectangle class:
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() { }
}
How would I go about implementing the undo and redo functions for this class in a way that it should be able to revert the rectangle to its previous state without the user mentioning what method was last used. I have a vague idea that involves using a stack but I'm stuck on how to actually code it. My second question is I'm not sure if my constructor is correct, I initialize everything to null without giving any parameters because I want people to use the getters/setters instead. Please help.
答案1
得分: 1
你可以将状态保存在一个数组中，并从中恢复矩形。
public class Rectangle () {
private states: List<Rectangle> = new ArrayList(); // 我们在每次更新任何属性时都会保存矩形的状态
private int stateIndex = 0; // 这是当前矩形上活动状态的索引
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; // 当添加新状态到状态数组时，我们将状态索引增加一
this.height = h;
this.states.add(this); // 在设置任何属性值后添加状态
}
public void undo() {
if(this.stateIndex > 0){ // 仅在当前状态之前有可用状态时才进行撤消操作
this.stateIndex--; // 将当前索引减少一
this.height = this.states.get(stateIndex).height; // 从状态中设置属性
...
}
}
public void redo() {
if(this.stateIndex < states.size()){ // 可以在缓存中的可用状态之上继续进行
this.stateIndex++; // 增加当前状态索引
this.height = this.states.get(stateIndex).height; // 更新属性值
...
}
}
}
英文:
you can saave the state in an array and restore the rectangle from it
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
...
}
}
}
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