“Unfortunately your app has stopped” error in emulator

Question

I am a new to both Android App and Java and have been making a simple App, and all is going fine until i open my emulator and the following error appear "Unfortunately your app has stopped". Here is my main activity.java file:

package com.firstprogram;

import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.TextView;


public class MainActivity extends Activity {

LinearLayout layout1;
EditText number1text;
EditText number2text;
Button   calcButton;
TextView answerText;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState); 

    layout1 = new LinearLayout (this);
    number1text = new EditText (this);
    number2text = new EditText (this);
    calcButton = new Button (this);
    answerText = new TextView (this);

    layout1.setOrientation(LinearLayout.VERTICAL);

    answerText.setText("0");
    calcButton.setText("Press to Multiply");

    calcButton.setOnClickListener((android.view.View.OnClickListener) multiply);

    layout1.addView(number1text);
    layout1.addView(number2text);
    layout1.addView(calcButton);
    layout1.addView(answerText);


    setContentView(layout1);  
}

private OnClickListener multiply = new OnClickListener() {

    @Override
    public void onClick (View v){
        String firstString = number1text.getText().toString();
        String secondString = number2text.getText().toString();
        double firstNumber = Double.parseDouble(firstString);
        double secondNumber = Double.parseDouble(secondString);
        double result = firstNumber * secondNumber;
        String resultString = String.valueOf(result);
        answerText.setText(resultString);
        }
    };
}

Log Cat code:

08-21 05:08:45.528: D/AndroidRuntime(809): Shutting down VM
08-21 05:08:45.528: W/dalvikvm(809): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
08-21 05:08:45.587: E/AndroidRuntime(809): FATAL EXCEPTION: main
08-21 05:08:45.587: E/AndroidRuntime(809): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.firstprogram/com.firstprogram.MainActivity}: java.lang.ClassCastException: com.firstprogram.MainActivity$1 cannot be cast to android.view.View$OnClickListener
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.os.Looper.loop(Looper.java:137)
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.app.ActivityThread.main(ActivityThread.java:5103)
08-21 05:08:45.587: E/AndroidRuntime(809):  at java.lang.reflect.Method.invokeNative(Native Method)
08-21 05:08:45.587: E/AndroidRuntime(809):  at java.lang.reflect.Method.invoke(Method.java:525)
08-21 05:08:45.587: E/AndroidRuntime(809):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
08-21 05:08:45.587: E/AndroidRuntime(809):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-21 05:08:45.587: E/AndroidRuntime(809):  at dalvik.system.NativeStart.main(Native Method)
08-21 05:08:45.587: E/AndroidRuntime(809): Caused by: java.lang.ClassCastException: com.firstprogram.MainActivity$1 cannot be cast to android.view.View$OnClickListener
08-21 05:08:45.587: E/AndroidRuntime(809):  at com.firstprogram.MainActivity.onCreate(MainActivity.java:37)
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.app.Activity.performCreate(Activity.java:5133)
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
08-21 05:08:45.587: E/AndroidRuntime(809):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
08-21 05:08:45.587: E/AndroidRuntime(809):  ... 11 more
08-21 05:08:45.823: D/dalvikvm(809): GC_FOR_ALLOC freed 278K, 16% free 2739K/3240K, paused 61ms, total 94ms
08-21 05:10:27.568: D/AndroidRuntime(860): Shutting down VM
08-21 05:10:27.568: W/dalvikvm(860): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
08-21 05:10:27.615: E/AndroidRuntime(860): FATAL EXCEPTION: main
08-21 05:10:27.615: E/AndroidRuntime(860): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.firstprogram/com.firstprogram.MainActivity}: java.lang.NullPointerException
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.os.Looper.loop(Looper.java:137)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.app.ActivityThread.main(ActivityThread.java:5103)
08-21 05:10:27.615: E/AndroidRuntime(860):  at java.lang.reflect.Method.invokeNative(Native Method)
08-21 05:10:27.615: E/AndroidRuntime(860):  at java.lang.reflect.Method.invoke(Method.java:525)
08-21 05:10:27.615: E/AndroidRuntime(860):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
08-21 05:10:27.615: E/AndroidRuntime(860):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-21 05:10:27.615: E/AndroidRuntime(860):  at dalvik.system.NativeStart.main(Native Method)
08-21 05:10:27.615: E/AndroidRuntime(860): Caused by: java.lang.NullPointerException
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.view.ViewGroup.addViewInner(ViewGroup.java:3505)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.view.ViewGroup.addView(ViewGroup.java:3377)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.view.ViewGroup.addView(ViewGroup.java:3353)
08-21 05:10:27.615: E/AndroidRuntime(860):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:286)
08-21 05:10:27.615: E/AndroidRuntime(860):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:276)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.app.Activity.setContentView(Activity.java:1915)
08-21 05:10:27.615: E/AndroidRuntime(860):  at com.firstprogram.MainActivity.onCreate(MainActivity.java:24)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.app.Activity.performCreate(Activity.java:5133)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
08-21 05:10:27.615: E/AndroidRuntime(860):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
08-21 05:10:27.615: E/AndroidRuntime(860):  ... 11 more
08-21 05:11:37.875: D/AndroidRuntime(907): Shutting down VM
08-21 05:11:37.875: W/dalvikvm(907): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
08-21 05:11:38.155: E/AndroidRuntime(907): FATAL EXCEPTION: main
08-21 05:11:38.155: E/AndroidRuntime(907): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.firstprogram/com.firstprogram.MainActivity}: java.lang.NullPointerException
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.os.Looper.loop(Looper.java:137)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.app.ActivityThread.main(ActivityThread.java:5103)
08-21 05:11:38.155: E/AndroidRuntime(907):  at java.lang.reflect.Method.invokeNative(Native Method)
08-21 05:11:38.155: E/AndroidRuntime(907):  at java.lang.reflect.Method.invoke(Method.java:525)
08-21 05:11:38.155: E/AndroidRuntime(907):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
08-21 05:11:38.155: E/AndroidRuntime(907):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-21 05:11:38.155: E/AndroidRuntime(907):  at dalvik.system.NativeStart.main(Native Method)
08-21 05:11:38.155: E/AndroidRuntime(907): Caused by: java.lang.NullPointerException
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.view.ViewGroup.addViewInner(ViewGroup.java:3505)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.view.ViewGroup.addView(ViewGroup.java:3377)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.view.ViewGroup.addView(ViewGroup.java:3353)
08-21 05:11:38.155: E/AndroidRuntime(907):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:286)
08-21 05:11:38.155: E/AndroidRuntime(907):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:276)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.app.Activity.setContentView(Activity.java:1915)
08-21 05:11:38.155: E/AndroidRuntime(907):  at com.firstprogram.MainActivity.onCreate(MainActivity.java:23)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.app.Activity.performCreate(Activity.java:5133)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
08-21 05:11:38.155: E/AndroidRuntime(907):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
08-21 05:11:38.155: E/AndroidRuntime(907):  ... 11 more
08-21 05:53:02.416: D/AndroidRuntime(971): Shutting down VM
08-21 05:53:02.416: W/dalvikvm(971): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
08-21 05:53:02.469: E/AndroidRuntime(971): FATAL EXCEPTION: main
08-21 05:53:02.469: E/AndroidRuntime(971): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.firstprogram/com.firstprogram.MainActivity}: java.lang.ClassCastException: com.firstprogram.MainActivity$1 cannot be cast to android.view.View$OnClickListener
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.os.Looper.loop(Looper.java:137)
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.app.ActivityThread.main(ActivityThread.java:5103)
08-21 05:53:02.469: E/AndroidRuntime(971):  at java.lang.reflect.Method.invokeNative(Native Method)
08-21 05:53:02.469: E/AndroidRuntime(971):  at java.lang.reflect.Method.invoke(Method.java:525)
08-21 05:53:02.469: E/AndroidRuntime(971):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
08-21 05:53:02.469: E/AndroidRuntime(971):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-21 05:53:02.469: E/AndroidRuntime(971):  at dalvik.system.NativeStart.main(Native Method)
08-21 05:53:02.469: E/AndroidRuntime(971): Caused by: java.lang.ClassCastException: com.firstprogram.MainActivity$1 cannot be cast to android.view.View$OnClickListener
08-21 05:53:02.469: E/AndroidRuntime(971):  at com.firstprogram.MainActivity.onCreate(MainActivity.java:36)
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.app.Activity.performCreate(Activity.java:5133)
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
08-21 05:53:02.469: E/AndroidRuntime(971):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
08-21 05:53:02.469: E/AndroidRuntime(971):  ... 11 more
08-21 06:00:07.957: D/AndroidRuntime(1010): Shutting down VM
08-21 06:00:08.016: W/dalvikvm(1010): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
08-21 06:00:08.055: E/AndroidRuntime(1010): FATAL EXCEPTION: main
08-21 06:00:08.055: E/AndroidRuntime(1010): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.firstprogram/com.firstprogram.MainActivity}: java.lang.ClassCastException: com.firstprogram.MainActivity$1 cannot be cast to android.view.View$OnClickListener
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.os.Looper.loop(Looper.java:137)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.app.ActivityThread.main(ActivityThread.java:5103)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at java.lang.reflect.Method.invokeNative(Native Method)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at java.lang.reflect.Method.invoke(Method.java:525)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at dalvik.system.NativeStart.main(Native Method)
08-21 06:00:08.055: E/AndroidRuntime(1010): Caused by: java.lang.ClassCastException: com.firstprogram.MainActivity$1 cannot be cast to android.view.View$OnClickListener
08-21 06:00:08.055: E/AndroidRuntime(1010):     at com.firstprogram.MainActivity.onCreate(MainActivity.java:36)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.app.Activity.performCreate(Activity.java:5133)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
08-21 06:00:08.055: E/AndroidRuntime(1010):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
08-21 06:00:08.055: E/AndroidRuntime(1010):     ... 11 more

Answer 1

The interesting line in your logcat is :

Caused by: java.lang.ClassCastException: com.firstprogram.MainActivity$1 cannot be cast to android.view.View$OnClickListener

There are multiple OnClickListener definitions in the Android framework, and it seems you're not using the right one.

If you want to use View.OnClickListener then you should use :

private View.OnClickListener multiply = new View.OnClickListener() {
    ....
}

Answer 2

Your class OnClickListener does not inherit from android.view.View.OnClickListener

You should better implements android.view.View.OnClickListener in your class, and override the method like that:

public class MainActivity extends Activity implements OnClickListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState); 

   //Do your stuff
   calcButton.setOnClickListener(this);
}

 @Override
 public void onClick (View v){
 //handle the event
 }

Answer 3

As Vimal said it's not a good idea to generate your GUI this way use XML. However, try this:

calcButton.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
    String firstString = number1text.getText().toString();
    String secondString = number2text.getText().toString();          
    double firstNumber = Double.parseDouble(firstString);
    double secondNumber = Double.parseDouble(secondString);
    double result = firstNumber * secondNumber;
    String resultString = String.valueOf(result);
    answerText.setText(resultString);   
}

});