小编Lig*_*keE的帖子

好的,所以我在Android Studio上有一个项目,但是当我在模拟器上运行应用程序时,它会崩溃.在堆栈跟踪中,主活动类有一个类未找到的异常,根据我的理解,它指向仅包含if语句的右括号的行.

这是堆栈跟踪:

02-21 14:49:44.498    2362-2362/com.example.user.assignment1 E/AndroidRuntime? FATAL EXCEPTION: main
Process: com.example.user.assignment1, PID: 2362
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.user.assignment1/com.example.user.assignment1.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.example.user.assignment1.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.user.assignment1-2/base.apk"],nativeLibraryDirectories=[/vendor/lib, /system/lib]]
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
        at android.app.ActivityThread.access$800(ActivityThread.java:144)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
 Caused by: java.lang.ClassNotFoundException: Didn't find class "com.example.user.assignment1.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.user.assignment1-2/base.apk"],nativeLibraryDirectories=[/vendor/lib, /system/lib]]
        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
        at   android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at …

我想在用户按下某个键时执行某个功能.这将在控制台中运行,代码使用Java.我该怎么做呢？我几乎没有关键按键/键盘的知识,所以我也可以使用一个解释.