java.lang.nullpointerexception error: app crashes
===

I am having a problem with my app crashing after I press my radio button.
The logcat says my error is java.lang.nullpointerexception.
I have included my logcat, java where error occured, and manifest.
I originally had problems with my radiobuttons where the program allowed me to have them both checked and impossible to uncheck. When I changed around the coding to include the oncheckchange listener the app now crashes whenever I press a radio button.

    07-17 18:09:37.067: W/dalvikvm(329): threadid=1: thread exiting with uncaught exception (group=0x40015560)
    07-17 18:09:37.077: E/AndroidRuntime(329): FATAL EXCEPTION: main
    07-17 18:09:37.077: E/AndroidRuntime(329): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.com.proto1/com.example.com.proto1.Voiceprompt}: java.lang.ClassNotFoundException: com.example.com.proto1.Voiceprompt in loader dalvik.system.PathClassLoader[/data/app/com.example.com.proto1-2.apk]
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at android.app.ActivityThread.access$1500(ActivityThread.java:117)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at android.os.Handler.dispatchMessage(Handler.java:99)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at android.os.Looper.loop(Looper.java:123)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at android.app.ActivityThread.main(ActivityThread.java:3683)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at java.lang.reflect.Method.invokeNative(Native Method)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at java.lang.reflect.Method.invoke(Method.java:507)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at dalvik.system.NativeStart.main(Native Method)
    07-17 18:09:37.077: E/AndroidRuntime(329): Caused by: java.lang.ClassNotFoundException: com.example.com.proto1.Voiceprompt in loader dalvik.system.PathClassLoader[/data/app/com.example.com.proto1-2.apk]
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at dalvik.system.PathClassLoader.findClass(PathClassLoader.java:240)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at java.lang.ClassLoader.loadClass(ClassLoader.java:551)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1561)
    07-17 18:09:37.077: E/AndroidRuntime(329): 	... 11 more





    package com.example.com.proto1;
    
    import android.app.Activity;
    import android.content.Intent;
    import android.media.MediaPlayer;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.RadioButton;
    import android.widget.RadioGroup;
    import android.widget.RadioGroup.OnCheckedChangeListener;
    
    public class VoicePrompts extends Activity implements OnCheckedChangeListener {
    
    	RadioButton on, off, onc, offc;
    
    	// Button Sound
    	final MediaPlayer buttonSound1 = MediaPlayer.create(VoicePrompts.this,
    			R.raw.vpo);
    	final MediaPlayer buttonSound2 = MediaPlayer.create(VoicePrompts.this,
    			R.raw.vpof);
    	final MediaPlayer buttonSound3 = MediaPlayer.create(VoicePrompts.this,
    			R.raw.vpoc);
    	final MediaPlayer buttonSound4 = MediaPlayer.create(VoicePrompts.this,
    			R.raw.vpofc);
    	{
    		// Setting up the button references
    
    		on = (RadioButton) findViewById(R.id.vbutton1);
    		off = (RadioButton) findViewById(R.id.vbutton2);
    		onc = (RadioButton) findViewById(R.id.vbutton1);
    		offc = (RadioButton) findViewById(R.id.vbutton2);
    	}
    
    	@Override
    	protected void onCreate(Bundle savedInstanceState) {
    		// TODO Auto-generated method stub
    		super.onCreate(savedInstanceState);
    		setContentView(R.layout.voiceprompts);
    	}
    
    	public void onCheckedChanged(RadioGroup arg0, int checkedId) {
    		// TODO Auto-generated method stub
    		switch (checkedId) {
    		case R.id.vbutton1:
    			on.setOnLongClickListener(new View.OnLongClickListener() {
    
    				public boolean onLongClick(View v) {
    					// TODO Auto-generated method stub
    					try {
    						buttonSound1.prepare();
    						buttonSound1.start();
    						startActivity(new Intent("android.intent.action.VPON"));
    
    					} catch (Exception e) {
    
    					}
    					return false;
    				}
    			});
    
    			onc.setOnClickListener(new View.OnClickListener() {
    
    				public void onClick(View v) {
    					// TODO Auto-generated method stub
    					try {
    						buttonSound3.prepare();
    						buttonSound3.start();
    						startActivity(new Intent("android.intent.action.VPON"));
    					} catch (Exception e) {
    
    					}
    					;
    
    				}
    			});
    
    			break;
    		case R.id.vbutton2:
    
    			off.setOnLongClickListener(new View.OnLongClickListener() {
    
    				public boolean onLongClick(View v) {
    					// TODO Auto-generated method stub
    					try {
    						buttonSound2.prepare();
    						buttonSound2.start();
    						startActivity(new Intent("android.intent.action.VPOFF"));
    					} catch (Exception e) {
    
    					}
    					;
    					return false;
    
    				}
    			});
    
    			offc.setOnClickListener(new View.OnClickListener() {
    
    				public void onClick(View v) {
    					// TODO Auto-generated method stub
    					try {
    						buttonSound4.prepare();
    						buttonSound4.start();
    						startActivity(new Intent("android.intent.action.VPOFF"));
    					} catch (Exception e) {
    
    					}
    					;
    
    				}
    			});
    
    			break;
    		}
    
    		off.setOnLongClickListener(new View.OnLongClickListener() {
    
    			public boolean onLongClick(View v) {
    				// TODO Auto-generated method stub
    				try {
    					buttonSound2.prepare();
    					buttonSound2.start();
    					startActivity(new Intent("android.intent.action.VPOFF"));
    				} catch (Exception e) {
    
    				}
    				;
    				return false;
    
    			}
    		});
    
    		offc.setOnClickListener(new View.OnClickListener() {
    
    			public void onClick(View v) {
    				// TODO Auto-generated method stub
    				try {
    					buttonSound4.prepare();
    					buttonSound4.start();
    					startActivity(new Intent("android.intent.action.VPOFF"));
    				} catch (Exception e) {
    
    				}
    				;
    
    			}
    		});
    
    	}
    
    }






    <manifest xmlns:android="http://schemas.android.com/apk/res/android"
        package="com.example.com.proto1"
        android:versionCode="1"
        android:versionName="1.0" >
    
        <uses-sdk
            android:minSdkVersion="8"
            android:targetSdkVersion="15" />
    
        <application
            android:icon="@drawable/ic_launcher"
            android:label="@string/app_name"
            android:theme="@style/AppTheme" >
            <activity
                android:name=".mainj"
                android:label="@string/title_activity_mainj" >
                <intent-filter>
                    <action android:name="android.intent.action.MAIN" />
    
                    <category android:name="android.intent.category.LAUNCHER" />
                </intent-filter>
            </activity>
            <activity
                android:name=".menu"
                android:label="@string/app_name" >
                <intent-filter>
                    <action android:name="android.intent.action.MENU" />
    
                    <category android:name="android.intent.category.DEFAULT" />
                </intent-filter>
            </activity>
            <activity
                android:name=".Infoactive"
                android:label="@string/app_name" >
                <intent-filter>
                    <action android:name="android.intent.action.INFOSCREEN" />
    
                    <category android:name="android.intent.category.DEFAULT" />
                </intent-filter>
            </activity>
            <activity
                android:name=".VoicePrompts"
                android:label="@string/app_name" >
                <intent-filter>
                    <action android:name="android.intent.action.VOICEPROMPTS" />
    
                    <category android:name="android.intent.category.DEFAULT" />
                </intent-filter>
            </activity>
            <activity
                android:name=".VPon"
                android:label="@string/app_name" >
                <intent-filter>
                    <action android:name="android.intent.action.VPON" />
    
                    <category android:name="android.intent.category.DEFAULT" />
                </intent-filter>
            </activity>
            <activity
                android:name=".VPoff"
                android:label="@string/app_name" >
                <intent-filter>
                    <action android:name="android.intent.action.VPOFF" />
    
                    <category android:name="android.intent.category.DEFAULT" />
                </intent-filter>
            </activity>
        </application>
    
    </manifest>