Question

我刚刚开始Java编程，我正在关注这个例子，我不断得到这个“无法从静态内容引用的非静态变量”错误。这段代码应该打印出节奏，速度和档位。我在Bicycle bike1=new Bicycle();和Bicycle bike2=new Bicycle();收到错误。这是代码：

public class BicycleDemo 
{

/**
 * @param args the command line arguments
 */
public static void main(String[] args) 
{
    // TODO code application logic here
    Bicycle bike1= new Bicycle();
    Bicycle bike2= new Bicycle();

    bike1.changeCadence(50);
    bike1.speedUp(10);
    bike1.changeGear(2);
    bike1.printStatments();

    bike2.changeCadence(40);
    bike2.speedUp(12);
    bike2.applyBreaks(3);
    bike2.printStatments();
}

class Bicycle
{
   int cadence=0;
   int speed=0;
   int gear=1;

   void changeCadence(int value)
   {
       cadence=value;
   }
   void changeGear(int value)
   {
       gear=value;
   }
   void speedUp(int increment)
   {
       speed=speed+increment;
   }
   void applyBreaks(int decrement)
   {
       speed=speed-decrement;
   }
   void printStatments()
   {
       System.out.println("Cadence:"+cadence+"Speed:"+speed+"Gear:"+gear);
   }
}

Answer 1

问题是Bicycle类是一个内部类，不能在static方法中直接实例化。只需将其移到BicycleDemo类：

之外

public class BicycleDemo {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args)  {
        // TODO code application logic here
        Bicycle bike1= new Bicycle();
        Bicycle bike2= new Bicycle();

        bike1.changeCadence(50);
        bike1.speedUp(10);
        bike1.changeGear(2);
        bike1.printStatments();

        bike2.changeCadence(40);
        bike2.speedUp(12);
        bike2.applyBreaks(3);
        bike2.printStatments();
    }
}

//note the braces ( } ) up here

class Bicycle {
    //definition here...
}

Answer 2

将class Bicycle更改为static class Bicycle，或者最好将其移至单独的文件（Bicycle.java）。

Answer 3

如果没有引用外部类的对象，则无法访问非静态内部类。在这种情况下，您无法实例化Bicycle bike1= new Bicycle();

您在静态上下文中工作（public static void main（String [] args）），因此您必须首先创建外部类（BicycleDemo）的实例，然后创建内部类的实例。在这种情况下，您需要写：

BicycleDemo demo = new BicycleDemo ();

Bicycle bike1= demo.new Bicycle();
Bicycle bike2= demo.new Bicycle();

...

非静态变量误差

3 个答案: