为什么 Java 将我的第二个实例的参数分配给 class 的两个实例？

Question

我正在学习入门级大学编程class，这可能是一个新手问题，但我无法在其他地方找到答案，也无法弄清楚为什么 Java正在将我的第二个 Conveyor 实例的参数分配给两个实例。

这是我的传送带class:

    public class Conveyor
    {
       //fields
       private static String type;
       private static double speed; //Speed is measured in m/s (meters/second)
       
       //constructors
       public Conveyor(String type, double speed)
       {
          this.type = type;
          this.speed = 0;
          this.speed = setSpeed(speed);
       }
       
       //methods
       public String getType()
       {
          return this.type;
       }
       
       public double getSpeed()
       {
          return this.speed;
       }
       
       public double setSpeed(double speed)
       {  
          if(speed <= 0)
          {
             this.speed = this.speed;
          }
          else
          {
             this.speed = speed;
          }
          
          return this.speed;
       }
       
       public double timeToTransport(double distance)
       {
          double t = distance / getSpeed();
          return t;
       }
    }

用于测试它的传送带应用程序：

    public class ConveyorApp
    {
       public static void main(String[] args)
       {
          Conveyor c1 = new Conveyor("flat belt",0.9);
          Conveyor c2 = new Conveyor("roller", -0.5);
          
          System.out.printf("Conveyor 1: %s conveyor with a speed of %.1f\n", c1.getType(), c1.getSpeed());
          System.out.printf("Time to transport an item 50m: %.1f\n\n", c1.timeToTransport(50));
          
          System.out.printf("Conveyor 2: %s conveyor with a speed of %.1f\n", c2.getType(), c2.getSpeed());
          System.out.printf("Time to transport an item 50m: %.1f\n\n", c2.timeToTransport(50));
       }
    }

如果我将第二个实例移动到第一个实例的打印语句下方，它会产生预期的行为并打印：

    Conveyor 1: flat belt conveyor with a speed of 0.9
    Time to transport an item 50m: 55.6
    
    Conveyor 2: roller conveyor with a speed of 0.0
    Time to transport an item 50m: Infinity

否则按照上面显示的顺序，这是我的输出：

    Conveyor 1: roller conveyor with a speed of 0.0
    Time to transport an item 50m: Infinity
    
    Conveyor 2: roller conveyor with a speed of 0.0
    Time to transport an item 50m: Infinity

我做错了什么？

Answer 1

传送带 class 的字段被标记为静态字段，但听起来您希望它们表现为实例字段。

  public class Conveyor
    {
       //fields
       private String type;
       private double speed; //Speed is measured in m/s (meters/second)
       ...

只需像这样删除静态关键字就可以了！

为什么 Java 将我的第二个实例的参数分配给 class 的两个实例？

Why is Java assigning the parameters of my second instance to both instances of a class?

java

class

instance

instance-variables