在 Java 中实现状态更改的撤消

发布于 2024-11-17 19:57:37 字数 723 浏览 5 评论 0原文

我开始实现命令模式，希望得到一个有用的解决方案来解决我提供撤消操作的问题。现在我面临一个问题：

在涉及操作时实现撤消相当简单：当我将 5 添加到一个数字时，然后我减去 5。当我将一个对象添加到列表中时，然后我将其删除，等等在。但是如果我有一个完整的状态而不是列表之类的东西怎么办？

一个例子：我对类中线程的信息进行建模：

public class ThreadInfo implements Comparable<ThreadInfo> {

    final int id;
    String name;
    int priority;
    String state;
    int waitCount;
    // ...
}

某些信息不会改变，例如 id。如上所述，撤消 waitCount 很容易，只需减去即可。但是优先级或状态又如何呢？目前尚不清楚如何撤消这些信息。

我想到的唯一想法是：在初始化命令对象时，保留其对象中的旧状态：通过将相关数据传递到构造函数中：

public MyCommand(int priority, String state) {
   previousPriority = priority;
   previousState = state;
}

或者最好让 ThreadInfo 有一个列表国家和优先事项是当前的首要要素吗？

原文

I am starting to implementing the command pattern in the hope to get a useful solution to my problem of providing an undo operation. Now I am facing a certain issue:

Implementing undo when operations are involved are rather easy: when I've added 5 to a number then I subtract 5. When I've added an object to a list, then I remove it, and so on. But what if I have a total state and not something like a list?

An example: I model information about a thread in a class:

public class ThreadInfo implements Comparable<ThreadInfo> {

    final int id;
    String name;
    int priority;
    String state;
    int waitCount;
    // ...
}

Certain information does not change, for instance the id. Undoing the waitCount is easy as described above, just subtract. But what about priority or state? It is not clear how to undo these information.

The only idea I came up with: when initializing the command object, preserve the old state in it's object: by passing the relevant data into the constructor:

public MyCommand(int priority, String state) {
   previousPriority = priority;
   previousState = state;
}

Or would it be better to let ThreadInfo have a list of states and priorities with being the first elements the current?

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习惯成性 2024-11-24 19:57:37

只需保持旧状态即可。例如

 class ChangeFoo {
    ChangeFoo (Bar bar, foo newFoo){}
    void execute(){
        oldFoo = bar.getFoo();
        bar.setFoo(newFoo);
    }
    void undo(){
        bar.setFoo(oldFoo);
    }
 }

Just hold old state in command. for example

 class ChangeFoo {
    ChangeFoo (Bar bar, foo newFoo){}
    void execute(){
        oldFoo = bar.getFoo();
        bar.setFoo(newFoo);
    }
    void undo(){
        bar.setFoo(oldFoo);
    }
 }

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