向上转型的问题

Java code

package polymorphism.music;

public enum Note {
    MIDDLE_C, C_SHARP, B_FLAT; // Etc.
}


package polymorphism.music;


class Instrument {
  public void play(Note n) {
    System.out.println("Instrument.play()");
  }
}


package polymorphism.music;

// Wind objects are instruments
// because they have the same interface:
public class Wind extends Instrument {
  // Redefine interface method:
  public void play(Note n) {
    System.out.println("Wind.play() " + n);
  }
} 


package polymorphism.music;

public class Music {
  public static void tune(Instrument i) {
    // ...
    i.play(Note.MIDDLE_C);
  }
  public static void main(String[] args) {
    Wind flute = new Wind();
    tune(flute); // Upcasting
  }
}

结果：

D:\my java>javac -d . Instrument.java Music.java Wind.java Note.java

D:\my java>java Music
Exception in thread "main" java.lang.NoClassDefFoundError: Music
Caused by: java.lang.ClassNotFoundException: Music
  at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
  at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: Music. Program will exit.

我不明白为什么编译通过 但运行不了呢 那点出错了呢



------解决方案--------------------
CLASS文件没有找到Music
你看一下MUSIC.class文件在不在
------解决方案--------------------
路径不对......
如下:
D:\my java\polymorphism\music>javac -d . Instrument.java Music.java Wind.java No
te.java
D:\my java\polymorphism\music>java polymorphism.music.Music