Java错误:找不到符号

Question

我正在写一个程序，用"O“来显示灯的电平，但当我编译时，它显示”找不到符号“，我声明了”消息“和”亮度“，还有什么我遗漏的东西要声明吗？类灯和类TestLamp我保存在不同的文件中，当我编译灯时，它没有显示错误。但它在编译TestLamp时显示“找不到符号”

class Lamp {

    // Sub-task 1: Declare and initialize data member with default value
    int brightness=1;

    // Sub-task 2: Define a method to indicate the brightness level of lamp
    String getBrightness() {
        String message = "";
        while(brightness>0) { 
            brightness--;
            message += "O"; 
        } 

        return message;
    }

    // Sub-task 3: Define a method to update the brightness of the lamp
    void setBrightness(int b) {

        if(b<1 || b>5) 
            brightness=2;
        else
            brightness=b;

    }
}

class TestLamp {
    public static void main (String[] args) {
        // Sub-task 4: Declare and create 3 lamp objects
        Lamp lamp1,lamp2,lamp3;

        // Sub-task 5: Adjust the lamp brightness according to the requirement
        lamp1.setBrightness(3);
        lamp2.setBrightness(10);

        // Sub-task 6: Display the information of the created lamps
        lamp1.getBrightness();
        System.out.println("Lamp1"+lamp1.message);
        lamp2.getBrightness();
        System.out.println("Lamp2"+lamp2.message);
    }
}

Answer 1

您只需创建引用Lamp lamp1,lamp2,lamp3;，而不是先创建任何对象create object，如下所示

Lamp lamp1=new Lamp();

字符串消息的作用域在getBrightness()方法中，所以lamp1.message会给你一个错误

因此，要打印消息，可以在类级别定义String message，也可以使用lamp1.getBrightness()

请看下面的工作代码

class Lamp {

// Sub-task 1: Declare and initialize data member with default value
    int brightness=1;
    String message = "";
// Sub-task 2: Define a method to indicate the brightness level of lamp
String getBrightness() {

    while(brightness>0) { 
        brightness--;
        message += "O"; 
    } 


    return message;
}

// Sub-task 3: Define a method to update the brightness of the lamp
void setBrightness(int b) {

    if(b<1 || b>5) 
        brightness=2;
    else
        brightness=b;


}


  }

 class ddd {
public static void main (String[] args) {
    // Sub-task 4: Declare and create 3 lamp objects
    Lamp lamp1 = new Lamp();
    Lamp lamp2=new Lamp();

    // Sub-task 5: Adjust the lamp brightness according to the requirement
    lamp1.setBrightness(3);
    lamp2.setBrightness(10);

    // Sub-task 6: Display the information of the created lamps
    lamp1.getBrightness();
      System.out.println("Lamp1"+lamp1.message);
    lamp2.getBrightness();
      System.out.println("Lamp2"+lamp2.message);


}
      }

Answer 2

您使用了lamp1.message，但是在Lamp类中没有message字段。

此外，您没有初始化Lamp的实例，这将导致另一个编译时错误。(感谢JasonC，我太习惯IDE了，以至于我忘记了基本的东西)。

Answer 3

您还没有实例化您的lamp对象，并且您的Lamp类缺少message字段