应该是目录的问题应该把两个.java文件都放在Shapes的目录里。package的结构应该和文件目录结构一样。javac和java都应该在最上一级目录里执行，即Shapes的上一级目录。正确的结构应该是这样的: C:\home>dir Volume in drive C has no label. Volume Serial Number is 43C1-842F Directory of C:\home 06/23/2006 12:06 AM . 06/23/2006 12:06 AM .. 06/23/2006 12:06 AM Shapes 0 File(s) 0 bytes 3 Dir(s) 32,119,504,896 bytes free C:\home>dir Shapes Volume in drive C has no label. Volume Serial Number is 43C1-842F Directory of C:\home\Shapes 06/23/2006 12:06 AM . 06/23/2006 12:06 AM .. 06/23/2006 12:08 AM 0 BasicShape.java 06/23/2006 12:08 AM 0 Shape2D.java 2 File(s) 0 bytes 2 Dir(s) 32,119,504,896 bytes free C:\home>javac Shapes\Shape2D.java ...... C:\home>java Shapes.Shape2D ...... 当你编译Shapes\Shape2D.java时，javac会去找Shapes\Shape