java程序必须要有一个public类,而且是有且只能有一个~~public class Rectangle int l,w; int perimeter() return 2*(l+w); } int area() return l*w; } public static void main(String[] args) Rectangle rect=new Rectangle(); rect.l=10; rect.w=5; System.out.println("perimeter of rect ="+rect.perimeter()); System.out.println("area of rect ="+rect.area()); } }改成这样应该就可以了 class dog extends animal { private string furcolor; dog(string name,string furcolor) { super(name); this.furcolor = furcolor; } public void enjoy() { system.out.println("~~~~~~~~~~~dog"); } } class cat extends animal { private string eyescolor; cat(string name,string eyescolor) { super(name); this.eyescolor = eyescolor; } public void enjoy() { system.out.println("~~~~~~~~cat"); } } 那两个类要继承一个类,才可以用super()方法,如果还有问题请告知(最好列出错误段,这样方便分析)java 菜鸟问题Exception in thread "main" java.lang.NoClassDefFoundError: fang2 Caused by: java.lang.ClassNotFoundException: fang2 at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClassInternal(Unknown Source) 大哥你这是什么啊 !!??、把原码拿来看看吧 好像是说你的一些class没找到!!是不是没写主函数啊!!!!!public class Rectangle int l,w; public int perimeter() return 2*(l+w); } public int area() return l*w; } public static void main(String[] args) Rectangle rect=new Rectangle(); rect.l=10; rect.w=5; System.out.println("perimeter of rect ="+rect.perimeter()); System.out.println("area of rect ="+rect.area()); } }