java - 当我使用 javac 编译多个 .java 文件时，出现一些 "duplicate class"错误，但我在代码中找不到错误

Question

当我使用 javac 编译多个 .java 文件时，出现一些“重复类” 错误，但我在代码中找不到错误。

有四个.java文件，所有这些文件都位于Windows的同一个文件夹中。

1. MyApp.java 文件中的代码:

import dx.*;
import dx.shapes.*;

class MyApp {
    public static void main(String[] args) {
        System.out.println("This is a test application."); 

        Rectangle rect = new Rectangle(10, 20);
        rect.Speak();

        Circle circle = new Circle(15);
        circle.Speak();

        Worker worker = new Worker();
        worker.Speak();
    }
}

Rectangle.java 文件中的代码:

    package dx.shapes;

    public class Rectangle {
        private int x, y;
        private int width, height;

        public Rectangle() {
            this(0, 0, 1, 1);
        }
        public Rectangle(int width, int height) {
            this(0, 0, width, height);
        }
        public Rectangle(int x, int y, int width, int height) {
            this.x = x;
            this.y = y;
            this.width = width;
            this.height = height;
        }
        public void Speak(){
            System.out.println("I'm a rectangle, width:" + this.width + ", height:" + this.height);
        }
    }

Circle.java 文件中的代码:

package dx.shapes;

public class Circle {
    private int x, y;
    private int radius;

    public Circle() {
        this(0, 0, 10);
    }
    public Circle(int radius) {
        this(0, 0, radius);
    }
    public Circle(int x, int y, int radius) {
        this.x = x;
        this.y = y;
        this.radius = radius;
    }
    public void Speak(){
        System.out.println("I'm a circle, radius:" + this.radius);
    }
}

Worker.java 文件中的代码:

package dx;

public class Worker {
    public void Speak(){
        System.out.println("I'm a worker.");
    }
}

在Windows命令行中，我使用javac来编译这些源代码:

javac MyApp.java Rectangle.java Circle.java Worker.java

但我得到的唯一的东西是错误列表:

Rectangle.java:3: error: duplicate class: dx.shapes.Rectangle
public class Rectangle {
       ^
MyApp.java:8: error: cannot access Rectangle
        Rectangle rect = new Rectangle(10, 20);
        ^
  bad source file: .\Rectangle.java
    file does not contain class Rectangle
    Please remove or make sure it appears in the correct subdirectory of the sourcepath.
Circle.java:3: error: duplicate class: dx.shapes.Circle
public class Circle {
       ^
MyApp.java:11: error: cannot access Circle
        Circle circle = new Circle(15);
        ^
  bad source file: .\Circle.java
    file does not contain class Circle
    Please remove or make sure it appears in the correct subdirectory of the sourcepath.
Worker.java:3: error: duplicate class: dx.Worker
public class Worker {
       ^
MyApp.java:14: error: cannot access Worker
        Worker worker = new Worker();
        ^
  bad source file: .\Worker.java
    file does not contain class Worker
    Please remove or make sure it appears in the correct subdirectory of the sourcepath.
6 errors

我不知道出了什么问题。为什么？

Answer 1

请引用编译器的文档:Arrangement of Source Code

主要:

When classes and interfaces are organized into a package, the package is represented as a directory, and any subpackages are represented as subdirectories.

假设您的根源目录是src，文件应排列为

src/
 |
 + - MyApp.java
 |
 + = dx/ 
      |
      + - Worker.java
      |
      + = shapes/
            |
            + - Circle.java
            + - Rectangle.java

要将更改编译到 src 目录并使用:

/src> javac *.java dx/*.java dx/shapes/*java

或者，对于 Windows:

C:\src>javac *.java dx\*.java dx\shapes\*java

由于 MyApp 中引用了所有类，因此您只需编译该文件，编译器就会找到并编译其他类:

src> javac MyApp.java

更好地立即编译所有文件，因为(相同的文档):

The order of source files specified on the command line or in an argument file is not important. javac will compile the files together, as a group, and will automatically resolve any dependencies between the declarations in the various source files.