访问超类中方法的变量

Question

我有一个包含 Animal 类以及 Dog 和 Cat 子类的基本代码。我有一个说话的方法。 speak 方法接收一个字符串，并返回一个猫狗“语言”的字符串。如果字符的 ascii 码是偶数，则返回“uff”，如果不是，则返回“vau”。当我重写该方法时，我想从 Dog 类中设置oddSound 和 evenSound，但我找不到合适的方法来执行此操作。
这段代码来自 Animal 类：

public String speak(String what){
    String speakableString = new String();
    String oddSound = new String();
    String evenSound = new String();

    for (int i = 0; i < what.length(); i++) {
        if((((int) what.charAt(i)) & 1) == 1){ 
            speakableString.concat(oddSound); 
        }else if ((((int) what.charAt(i)) & 1) == 0){
            speakableString.concat(evenSound);
        }
    }

    speakableString = speakableString.substring(0, speakableString.length()-1);
    return speakableString;
}

这段代码来自 Dog 类：

public String speak(String what){
    //set oddSound = "vau"
    //set evenSound = "uff"
    return super.speak(what);
}

Answer 1

在Animal 类中，有两个受保护的字段，

protected String oddSound;
protected String evenSound;

然后，在Dog 和Cat 类中，您可以设置这些字段：

oddSound = "woof";
evenSound = "woofwoof"

然后，在speak() 方法中，您可以简单地使用this.oddSound 和this.evenSound

Answer 2

您可以将它们保留为数据成员，并在各自的构造函数中设置它们：

public class Animal {
    private String oddSound;
    private String evenSound;

    protected Animal (String oddSound, String evenSound) {
        this.oddSound = oddSound;
        this.evenSound = evenSound;
    }

    public String speak(String what){
        String speakableString = new String();

        for (int i = 0; i < what.length(); i++) {
            if((((int) what.charAt(i)) & 1) == 1){ 
                speakableString = speakableString.concat(oddSound); 
            }else if ((((int) what.charAt(i)) & 1) == 0){
                speakableString = speakableString.concat(evenSound);
            }
        }
}

public class Dog extends Animal {
    public Dog() {
        super ("uff", "vau");
    }
}

Answer 3

Animal 类应该声明你的 speak 方法，因为这对 Dog 和 Cat 类都是通用的。

public class Animal {
    String oddSound;
    String evenSound;

    public Animal(String oddSound, String evenSound) {
        this.oddSound = oddSound;
        this.evenSound = evenSound;
    }

    public String speak(String what){
        String speakableString = new String();

        for (int i = 0; i < what.length(); i++) {
            if((((int) what.charAt(i)) & 1) == 1){ 
                speakableString = speakableString.concat(oddSound); 
            }else if ((((int) what.charAt(i)) & 1) == 0){
                speakableString = speakableString.concat(evenSound);
            }
        }

    speakableString = speakableString.substring(0, speakableString.length()-1);
    return speakableString;
    }
}

请记住，string.concat 方法会创建一个 new 对象，它不会修改调用它的实例。见String API Documentation

您的 Dog 和 Cat 类应仅在需要时定义或覆盖方法。看来您在他们的 speak 方法中所做的只是调用超级方法实现。你可以完全摆脱它。

如果您想扩展 Animal 类以提供新的方法或实现，请这样做：

public class Dog extends Animal {
    public Dog() {
        // This calls the super constructor, which sets the oddSound and evenSound fields
        super("vau", "uff");
    }

    // This section does nothing.
    // A method implementation which only calls its super implementation is ineffective.
    // If you were to provide a new implementation, this is where it would be.
    //public String speak(String what) {
    //  super.speak(what);  
    //}
}

Answer 4

您可以将您的 speak 实现分成两部分，以允许您传入要用于 oddSound 和 evenSound 的字符串。

public String speak(String what){
    return getSpeakableString(what, new String(), new String());
}
protected String getSpeakableString(String what, String oddSound, String evenSound){
    //this is just copied from what you had in your question, it likely doesn't do what you actually want.
    String speakableString = new String();
    for (int i = 0; i < what.length(); i++) {
        if((((int) what.charAt(i)) & 1) == 1){ 
            speakableString.concat(oddSound); 
        }else if ((((int) what.charAt(i)) & 1) == 0){
            speakableString.concat(evenSound);
        }
    }
    speakableString = speakableString.substring(0, speakableString.length()-1);
    return speakableString;
}

//in subclass
@Override
public String speak(String what){
    return getSpeakableString(what, "vau", "uff");
}