How to solve java.lang.NoClassDefFoundError?

Question

I\'ve tried both the example in Oracle\'s Java Tutorials. They both compile fine, but at run-time, both come up with this error:

Exception in thread \"main\"         


        

Answer 1

Check that if you have a static handler in your class. If so, please be careful, cause static handler only could be initiated in thread which has a looper, the crash could be triggered in this way:

1.firstly, create the instance of class in a simple thread and catch the crash.

2.then call the field method of Class in main thread, you will get the NoClassDefFoundError.

here is the test code:

public class MyClass{
       private static  Handler mHandler = new Handler();
       public static int num = 0;
}

in your onCrete method of Main activity, add test code part:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //test code start
    new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                MyClass myClass = new MyClass();
            } catch (Throwable e) {
                e.printStackTrace();
            }
        }
    }).start();

    try {
        Thread.sleep(1000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    MyClass.num = 3;
    // end of test code
}

there is a simple way to fix it using a handlerThread to init handler:

private static Handler mHandler;
private static HandlerThread handlerThread = new HandlerThread("newthread");
static {
    handlerThread.start();
    mHandler = new Handler(handlerThread.getLooper(), mHandlerCB);
}