Question

我正在做一个UML而且我不太确定如何做这些我应该这样做的mutator方法：

+turnOn(): void       //sets on to true
+turnOff(): void      //sets on to false
+channelUp(): void    //increases channel by 1 if on, rolls to 1 after maximum
+channelDown(): void  //decreases channel by 1 if on, rolls to maximum after 1
+volumeUp(): void     //increases the volume by 1 if on and less than maximum
+volumeDown(): void   //decreases volume by 1 if on and greater than 0
+toString( ): String  //returns the current state(instance variable values)

我的代码现在:(请记住mutator部分不对）

public class TV {
    private int volume;
    private int channel;
    private boolean on;
    private int maxVolume;
    private int maxChannel;

    TV() {
        volume = 1;
        channel = 1;
        on = false;
        maxVolume = 1;
        maxChannel = 1;
    }
    public int getChannel() {
        return channel;
    }

    public int getVolume() {
        return volume;
    }

    public boolean isOn() {
        return on;
    }

    public int getMaxChannel() {
        return maxChannel;
    }

    public int getMaxVolume() {
        return maxVolume;
    }
    public void setChannel(int i) {
        if (isOn() && i >= 1 && i <= maxChannel) channel = i;
    }

    public void setVolume(int i) {

        if (isOn() && i >= 0 && i <= maxVolume) volume = i;
    }

    public void setMaxChannel(int i) {
        maxChannel = i;
    }

    public void setMaxVolume(int i) {
        maxVolume = i;
    }

    // + turnOn() * * This is where the mutator methods begin I need help here * *

    // if (channel == maxChannel) channel = 1;
    // else channel++;

    //if (channel == 1) channel = max;
    //else channel--;

    // if (volume == maxVolume) volume = 1;
    // else channel++;
    //if (volume == 1) volume = max;
    // else channel--;

    public string toString() {
        return "channel: " + channel + "\nvolume: " + volume +
            "\non: " + on + "\nmax Channel: " + maxChannel +
            "\nmax Volume: " + maxVolume;
    }
}

Answer 1

Mutator通常意味着与'setter'相同的东西

所以在上面的代码中，'getter'将是：

public int getMaxChannel() {
  return maxChannel;
}

和'mutator'或'setter'将是：

public void setMaxChannel(int maxChannel) {
  this.maxChannel = maxChannel;
}

Answer 2

我们可以互换使用setter和mutator。

mutator方法用于设置私有字段的值。它跟随一个命名方案，在单词“set”前面加上方法的开头名称。这些方法没有返回类型并接受参数这是与其对应的私有字段相同的数据类型。该然后使用参数来设置该私有字段的值。

以下是mutators或setter的一些例子：

public void setMaxChannel(int i) {
        maxChannel = i;
    }

public void setChannel(int c) {
        channel=c;
    }

Answer 3

示例方法：

public void turnOn() {
   this.on = true;
}

public void channelUp() {
   if (on) {
      if (channel == maxChannel) {
         channel = 1;
      }
      else {
         channel++;
      }
   }
}

public void volumeDown() {
   if (on && volume > 0) {
      volume--;
   }
}

其他方法遵循相同的逻辑。

java中的字符串是对象，因此你的toString方法签名应该是public String toString()。

需要mutator方法我该怎么做

3 个答案: