异常截获: NoClassDefFoundError——How to Include A Jar File
前几天遇到这样一个问题：
我明明引入了一个jar包，ctrul+单击也能进入源码，却总在new类的时候（如：User user = new User()），出现NoClassDefFoundError，无法实例化类。
控制台打印堆栈如下：
11-15 16:41:00.495: E/AndroidRuntime(7757): FATAL EXCEPTION: main11-15 16:41:00.495: E/AndroidRuntime(7757): java.lang.NoClassDefFoundError: com/google/zxing/integration/android/IntentIntegrator11-15 16:41:00.495: E/AndroidRuntime(7757): at com.google.zxing.client.androidtest.ZXingTestActivity$3.onClick(ZXingTestActivity.java:139)11-15 16:41:00.495: E/AndroidRuntime(7757): at android.view.View.performClick(View.java:4084)11-15 16:41:00.495: E/AndroidRuntime(7757): at android.view.View$PerformClick.run(View.java:16966)11-15 16:41:00.495: E/AndroidRuntime(7757): at android.os.Handler.handleCallback(Handler.java:615)11-15 16:41:00.495: E/AndroidRuntime(7757): at android.os.Handler.dispatchMessage(Handler.java:92)11-15 16:41:00.495: E/AndroidRuntime(7757): at android.os.Looper.loop(Looper.java:137)11-15 16:41:00.495: E/AndroidRuntime(7757): at android.app.ActivityThread.main(ActivityThread.java:4928)11-15 16:41:00.495: E/AndroidRuntime(7757): at java.lang.reflect.Method.invokeNative(Native Method)11-15 16:41:00.495: E/AndroidRuntime(7757): at java.lang.reflect.Method.invoke(Method.java:511)11-15 16:41:00.495: E/AndroidRuntime(7757): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)11-15 16:41:00.495: E/AndroidRuntime(7757): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)11-15 16:41:00.495: E/AndroidRuntime(7757): at dalvik.system.NativeStart.main(Native Method)11-15 16:41:00.495: E/AndroidRuntime(7757): Caused by: java.lang.ClassNotFoundException: com.google.zxing.integration.android.IntentIntegrator11-15 16:41:00.495: E/AndroidRuntime(7757): at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:61)11-15 16:41:00.495: E/AndroidRuntime(7757): at java.lang.ClassLoader.loadClass(ClassLoader.java:501)11-15 16:41:00.495: E/AndroidRuntime(7757): at java.lang.ClassLoader.loadClass(ClassLoader.java:461)11-15 16:41:00.495: E/AndroidRuntime(7757): ... 12 more
可是，我明明引入了啊，也add到Build Path里面了，为什么还会报NoClassDefFoundError呢？
是我引入jar包的方法不对，放的位置不对，还是？
那么，如何引入一个jar文件呢（how to include a jar file）?
take the following steps, then you won't get the error:
1.Create a folder in the root of your project called libs.
2.Add the jar to that folder.
3.Right-click the jar and click to add to build path.
4.Clean your project.
5.Build project.
6.Run.
其实，在android project里面，在ADT的作用下，引入jar包，只需要将jar包拷入工程的libs目录下，不需要再add to build path，系统会自动将libs下的jar包添加到build path（实际上是添加到Android Dependencies这个library下）
哎，规范编程，“约定优于配置”，再也不会偷懒，把jar文件随便放了。
