我的代码给出了运行时错误！ 我是android编程的新手，谁能告诉我我的错误

Question

Can anyone explain what are errors in my android programme?

Logcat :

07-13 09:04:18.429: D/AndroidRuntime(274): Shutting down VM

07-13 09:04:18.429: W/dalvikvm(274): threadid=1: thread exiting with uncaught exception (group=0x4001d800)

07-13 09:04:18.469: E/AndroidRuntime(274): FATAL EXCEPTION: main

07-13 09:04:18.469: E/AndroidRuntime(274): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.firstapplication1/com.example.firstapplication1.StartingPoint}: java.lang.ClassCastException: android.widget.TextView

07-13 09:04:18.469: E/AndroidRuntime(274):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)

07-13 09:04:18.469: E/AndroidRuntime(274):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)

07-13 09:04:18.469: E/AndroidRuntime(274):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)

07-13 09:04:18.469: E/AndroidRuntime(274):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)

07-13 09:04:18.469: E/AndroidRuntime(274):  at android.os.Handler.dispatchMessage(Handler.java:99)

07-13 09:04:18.469: E/AndroidRuntime(274):  at android.os.Looper.loop(Looper.java:123)

07-13 09:04:18.469: E/AndroidRuntime(274):  at android.app.ActivityThread.main(ActivityThread.java:4627)

07-13 09:04:18.469: E/AndroidRuntime(274):  at java.lang.reflect.Method.invokeNative(Native Method)

07-13 09:04:18.469: E/AndroidRuntime(274):  at java.lang.reflect.Method.invoke(Method.java:521)

07-13 09:04:18.469: E/AndroidRuntime(274):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)

07-13 09:04:18.469: E/AndroidRuntime(274):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)

07-13 09:04:18.469: E/AndroidRuntime(274):  at dalvik.system.NativeStart.main(Native Method)

07-13 09:04:18.469: E/AndroidRuntime(274): Caused by: java.lang.ClassCastException: android.widget.TextView

07-13 09:04:18.469: E/AndroidRuntime(274):  at com.example.firstapplication1.StartingPoint.onCreate(StartingPoint.java:25)

07-13 09:04:18.469: E/AndroidRuntime(274):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)

07-13 09:04:18.469: E/AndroidRuntime(274):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)

07-13 09:04:18.469: E/AndroidRuntime(274):  ... 11 more
07-13 09:04:28.659: I/Process(274): Sending signal. PID: 274 SIG: 9

StartingPoint.java :

public class StartingPoint extends Activity {
int counter;
Button add;
Button sub;
TextView display;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    counter=0;
    add = (Button) findViewById(R.id.bAdd);
    sub = (Button) findViewById(R.id.bSub);
    display = (Button) findViewById(R.id.tvDisplay);
    add.setOnClickListener(new View.OnClickListener() {


        public void onClick(View v) {

            counter++;
            display.setText("Your Total is " + counter);
        }
    });
    sub.setOnClickListener(new View.OnClickListener() {


        public void onClick(View v) {

            counter--;
            display.setText("Your Total is " + counter);
        }
    });

}


public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.starting_point, menu);
    return true;
}

 }

Answer 1

You get a ClassCastException because you are casting your TextView to a Button here:

display = (Button) findViewById(R.id.tvDisplay);

You need to cast it to a TextView :

display = (TextView) findViewById(R.id.tvDisplay);

Answer 2

Change this

      display = (Button) findViewById(R.id.tvDisplay);
     // casting to textview to button. wrong

To

       display = (TextView) findViewById(R.id.tvDisplay);

Caused by: java.lang.ClassCastException: android.widget.TextView

Your display is TextView while initializing you have cast the same with Button

Answer 3

Change the following line in your code

display = (Button) findViewById(R.id.tvDisplay);

to

display = (TextView) findViewById(R.id.tvDisplay);

You cannot cast TextView to Button

Answer 4

Change

display = (Button) findViewById(R.id.tvDisplay);

to

display = (TextView) findViewById(R.id.tvDisplay);

Answer 5

This is a very simple mistake and it happens. Please update your IDE and ADT to latest because the new ADT catches these mistakes at coding time. It will save lot of your time in learning.