父类,子类 命名很重要——例子
代码如下:
class BBt{
public void en(){
System.out.println("TT.show()");
}
}
class Bb extends BBt {
public void en(){
System.out.println("Tt.show");
}
}
public class Test {
public static void toShow(Bb tt){
System.out.println("这边!!");
tt.en();
}
public static void main(String[] args){
Bb tt = new Bb();
toShow(tt);
}
}
运行如下:
以上一切正常,现在将父类 BBt 改为BB ,看结果
class BB{
public void en(){
System.out.println("TT.show()");
}
}
class Bb extends BB {
public void en(){
System.out.println("Tt.show");
}
}
public class Test {
public static void toShow(Bb tt){
System.out.println("这边!!");
tt.en();
}
public static void main(String[] args){
Bb tt = new Bb();
toShow(tt);
}
}
并没有报错,我们运行看看,打印结果如下:
java.lang.NoClassDefFoundError: com/study/test/BB (wrong name: com/study/test/Bb)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
at java.lang.Class.getMethod0(Class.java:3018)
at java.lang.Class.getMethod(Class.java:1784)
at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main"
Process finished with exit code 1
产生原因:NoClassDefFoundError错误的发生,是因为Java虚拟机在编译时能找到合适的类,而在运行时不能找到合适的类导致的错误。