java - java 中的纪念品。可变状态

Question

我正在尝试理解纪念品模式。为此，我正在尝试实现撤消功能。问题是，当我将发起者的旧状态保存在队列中并运行不同的函数时，保存状态会更改为当前状态。我真的需要帮助来理解我做错了什么。我怎样才能使 vector 不可变。

这是纪念品类。

package memento;

public class Memento
{
    private final boolean[] vectorState;

    public Memento(boolean[] vector) {vectorState = vector;}

    boolean[] getMemento() { return vectorState;}

}

发起者只需将 boolean vector 左移即可。(TRUE,FALSE,FALSE) 左移返回:(FALSE,FALSE,TRUE)。这就是实现。

package memento;

public class ShilftLeftOriginator
{
    private boolean[] vector;

    public ShilftLeftOriginator(boolean[] vector) {this.vector = vector;}

    public void execute()
    {
        final boolean firstValue = this.vector[0];
        for (int i = 1; i < this.vector.length; i++) {
            this.vector[i - 1] = this.vector[i];
        }
        this.vector[vector.length - 1] = firstValue;
    }


    public Memento saveToMemento() {return new Memento(vector);}

}

看门人:

package memento;

import java.util.Arrays;
import java.util.Deque;
import java.util.LinkedList;


public final class BooleanVector {
    private boolean[] vector;
    private Deque<Memento> mementoList = new LinkedList<>();

    public BooleanVector(boolean[] inputValues) {
        this.vector = inputValues;
    }


    @Override
    public boolean equals(Object obj) 
    {
        if (obj == null) return false;
        if (!(obj instanceof BooleanVector)) return false;
        BooleanVector otherVector = (BooleanVector) obj;
        return Arrays.equals(this.vector, otherVector.vector);
    }

    public void shiftLeft() 
    {
        ShilftLeftOriginator shiftLeft = new ShilftLeftOriginator(vector);
        mementoList.add(shiftLeft.saveToMemento());
        shiftLeft.execute(); // This is my Problem. After execute ist call the value(vector) in mementoList changes             
    }

    public void undo(){ this.vector =  mementoList.pop().getMemento();}

}

现在是测试类和我收到的错误。

package memento;

public class Main {

    public static void main(String[] args) {
        boolean[] inputValues = { false, true, false };
        BooleanVector vector = new BooleanVector(inputValues);

        vector.shiftLeft();

        boolean[] expectedValues = new boolean[] { true, false, false };
        BooleanVector expectedVector = new BooleanVector(expectedValues);

        if (!vector.equals(expectedVector)) {
            throw new IllegalStateException(vector.toString());
        } else {
            System.out.println("shiftleft working");
        }

        vector.undo();

        expectedValues = new boolean[] { false, true, false };
        expectedVector = new BooleanVector(expectedValues);

        if (!vector.equals(expectedVector)) {
            throw new IllegalStateException(vector.toString());
        } else {
            System.out.println("undo working");
        }

    }

}

控制台输出:

shiftleft working
Exception in thread "main" java.lang.IllegalStateException: [true, false, false]
    at memento.Main.main(Main.java:26)

Answer 1

问题是你总是在操作同一个数组。因此，如果向左移动，您存储在 Memento 对象中的数组也会向左移动，因为它们都是相同的数组。

要解决这个问题，请在 Memento 对象的构造函数中复制数组:

public Memento(boolean[] vector) {
    vectorState = Arrays.copyOf(vector, vector.length);
}

除此之外，你的类(class)似乎很困惑。 BooleanVector 和 ShilftLeftOriginator 是发起者，而 Main 是看护者。