Question

我是java的新手，我正在尝试创建一个程序来测试用户对2个随机频率之间的差异。一切都有效，除了当我试图获得2个频率的差异时，答案总是为0.我如何才能显示实际差异？这是我写的用来创建音调的类来计算差异：

public class Quiz{

    private PitchPlay one = new PitchPlay();
    private PitchPlay two = new PitchPlay();

    private int frequencyOne;
    private int frequencyTwo;

    private int dif = new Integer(Math.abs(frequencyTwo - frequencyOne));

public int run(){
    frequencyOne = new Integer((int)(Math.random() * 5000 + 50));
    frequencyTwo = new Integer((int)(Math.random() * 5000 + 50));
    return this.dif;
}

public int freqDif(){
    return this.dif;
}

public void playQuiz(){
    one.play(one.note(frequencyOne, 2, 15));//note(frequency, duration, volume)
    two.play(two.note(frequencyTwo, 2, 15));
}
}

以下是使用测验类的课程：

public class Action implements ActionListener{
Quiz one = new Quiz();

public void actionPerformed (ActionEvent e){
        if(e.getSource() == playSoundButton)
        {
            if(answerResponse.getText().compareTo("Correct!")  == 0 || answerResponse.getText().compareTo("Play and Listen...") == 0)
            {
                one.run();
                one.playQuiz();
            }
            else
            {
                one.playQuiz();
            }
        }
        if(e.getSource() == submitButton)
        {   
            String responseText = new String(responseField.getText());
            if(responseText !=null && !"".equals(responseText)){
                try{
                    Integer responseNumber = Integer.parseInt(responseText);

            if(responseNumber == one.freqDif())
            {
                    answerResponse.setText("Correct!");
                    answerResponse.setVisible(true);
            }
            else
            {
                answerResponse.setText("Wrong Answer. The difference is " + one.freqDif() + " hertz.");
                answerResponse.setVisible(true);
            }
                }catch(NumberFormatException f){
                    f.printStackTrace(System.out);
                }
            }



        }

    }
}

Answer 1

private int dif = new Integer(Math.abs(frequencyTwo - frequencyOne));

这是在创建变量时计算的，而不是在使用变量时计算的。您需要在分配变量后进行计算。

Answer 2

您的代码存在以下问题：

正如其他人所说，行
```
private int dif = new Integer(Math.abs(frequencyTwo - frequencyOne));
```
创建一个变量并指定一个从其他两个变量计算出来的值。使用创建时其他变量的值。每次这两个变量的值发生变化时，都需要重新计算。这不会自动发生。
new Integer(...)创建一个Integer对象。随后将此对象分配给int变量时，将从对象中取出该值。这会为您的代码增加一些不必要的内存和运行时间。相反，您应该直接分配给您的变量。例如，
```
frequencyOne = (int)(Math.random() * 5000 + 50);
```

方法始终返回零

2 个答案: