爲什麼試圖使用mediaplayer時java.lang.ClassNotFoundException？

Question

我正試圖與媒體播放器運行程序。
爲什麼我得到這個異常？請幫忙。

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.android.myplayer/com.andr 
oid.myplayer.MediaPlayerDemo_video}: java.lang.ClassNotFoundException: com.android.myplayer.MediaPlayerDemo_video in loader dal 
vik.system.PathClassLoader@349c48d8 
E/AndroidRuntime(4102):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2417) 
E/AndroidRuntime(4102):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512) 
E/AndroidRuntime(4102):  at android.app.ActivityThread.access$2200(ActivityThread.java:119) 
E/AndroidRuntime(4102):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863) 
E/AndroidRuntime(4102):  at android.os.Handler.dispatchMessage(Handler.java:99) 
E/AndroidRuntime(4102):  at android.os.Looper.loop(Looper.java:123) 
E/AndroidRuntime(4102):  at android.app.ActivityThread.main(ActivityThread.java:4363) 
E/AndroidRuntime(4102):  at java.lang.reflect.Method.invokeNative(Native Method) 
E/AndroidRuntime(4102):  at java.lang.reflect.Method.invoke(Method.java:521) 
E/AndroidRuntime(4102):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 
E/AndroidRuntime(4102):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
E/AndroidRuntime(4102):  at dalvik.system.NativeStart.main(Native Method) 
E/AndroidRuntime(4102): Caused by: java.lang.ClassNotFoundException: com.android.myplayer.MediaPlayerDemo_video in loader dalv 
ik.system.PathClassLoader@349c48d8 
E/AndroidRuntime(4102):  at dalvik.system.PathClassLoader.findClass(PathClassLoader.java:243) 
E/AndroidRuntime(4102):  at java.lang.ClassLoader.loadClass(ClassLoader.java:573) 
E/AndroidRuntime(4102):  at java.lang.ClassLoader.loadClass(ClassLoader.java:532) 
E/AndroidRuntime(4102):  at android.app.Instrumentation.newActivity(Instrumentation.java:1021) 
E/AndroidRuntime(4102):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2409) 
E/AndroidRuntime(4102):  ... 11 more 

Answer 1

這個異常通常意味着一個CLASSPATH問題：當JVM需要加載它時，類加載器還沒有被告知在哪裏找到那個類。所以你需要弄清楚哪個JAR包含這個類並將它添加到CLASSPATH中。