When I use javac to complile several .java files, I got some "duplicate class" errors, but I can't find errors in my code

Question

When I use javac to complile several .java files, I got some "duplicate class" errors, but I can't find errors in my code.

There are four .java files, all these files are in the same folder in Windows.

1. Code in MyApp.java file:

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();
    }
}

2. Code in Rectangle.java file:

    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);
        }
    }

3. Code in Circle.java file:

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);
    }
}

4. Code in Worker.java file:

package dx;

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

In Windows command line, I use javac to compile these source codes:

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

But the only thing I got is a list of errors:

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

I don't know what is wrong. Why?

Answer 1

Please refer to the documentation of compiler: Arrangement of Source Code

Mainly:

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

Assuming your root source directory is src, the files should be arranged as

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

To compile change to the src directory and use:

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

or, for Windows:

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

Since all classes are being referenced in MyApp, you can just compile that file and the compiler will find and compile the other classes:

src> javac MyApp.java

Better compile all files at once since (same documentation):

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.