为什么我的两个变量的比较if语句行不通？[副本]

Question

在下面的代码中，一旦执行，它将根据随机数生成器更改对象diet的状态hek。我还有一个undo()函数，它在运行时工作得非常好。

我要做的是：当对象的状态发生更改，但以前的状态prevdiet等于更改后的状态currentdiet时，我希望程序调用undo()。

import java.util.Random;
import javax.swing.JOptionPane;

public class changeDietCom implements Command {

    Hek hek;
    Random rand = new Random();
    int x;
    DietBehaviour prevDiet;
    DietBehaviour currentDiet;

    public changeDietCom(Hek hek) {
        this.hek = hek;
    }

    public void execute() {

        x = rand.nextInt(3) + 1;

        prevDiet = hek.getDietBehaviour();
        if (x == 1) {

            hek.setDietBehaviour(new Enemies());
            JOptionPane.showMessageDialog(null, "Hek's diet has been changed!", "Changing diet", JOptionPane.INFORMATION_MESSAGE);

            currentDiet = hek.getDietBehaviour();
            hek.performDiet();

            if (prevDiet == currentDiet) {
                JOptionPane.showMessageDialog(null, "Diet hasn't changed!", "Current Diet = Prev Diet", JOptionPane.INFORMATION_MESSAGE);
                undo();
            }
        }
        else if (x == 2) {

            hek.setDietBehaviour(new ArmouredKnights());
            JOptionPane.showMessageDialog(null, "Hek's diet has been changed!", "Changing diet", JOptionPane.INFORMATION_MESSAGE);

            currentDiet = hek.getDietBehaviour();
            hek.performDiet();

            if (prevDiet == currentDiet) {
                JOptionPane.showMessageDialog(null, "Diet hasn't changed!", "Current Diet = Prev Diet", JOptionPane.INFORMATION_MESSAGE);
                undo();
            }
        }
        else if (x == 3) {

            hek.setDietBehaviour(new BigMac());
            JOptionPane.showMessageDialog(null, "Hek's diet has been changed!", "Changing diet", JOptionPane.INFORMATION_MESSAGE);

            currentDiet = hek.getDietBehaviour();
            hek.performDiet();

            if (prevDiet == currentDiet) {
                JOptionPane.showMessageDialog(null, "Diet hasn't changed!", "Current Diet = Prev Diet", JOptionPane.INFORMATION_MESSAGE);
                undo();
            }
        }
    }

    public void undo() {
        JOptionPane.showMessageDialog(null, "Undoing diet change...", "Undoing Diet Change", JOptionPane.INFORMATION_MESSAGE);
        hek.setDietBehaviour(prevDiet);
        hek.performDiet();
    }
}

但是，只要在运行时上一个状态prevdiet和当前状态currentdiet彼此相等，if语句就不会返回true，我看不出为什么不返回？谁能告诉我为什么和如何解决这个问题吗？

我应该提到的是，我正在使用命令模式来设计程序的这一部分。

Answer 1

使用if(prevDiet==currentDiet){，可以比较对象引用而不是实际值。请使用if(prevDiet.equals（currentDiet)){，并确保重写dietBehaviory的equals()方法。

请注意，当重写equals()时，还应该重写hashcode()，并且实现应该是一致的。有关这方面的更多信息可以在这里找到。