title: Beginner Android Development: findViewById issue
body: <p>I get the following error message when running my basic application.
  The application consists of a button called button1 and a textView called topLeft. </p>
  
  <pre><code>07-01 15:33:02.754: D/AndroidRuntime(2334): Shutting down VM 07-01 15:33:02.754: W/dalvikvm(2334): threadid=1: thread exiting with
  uncaught exception (group=0x40a13300) 07-01 15:33:02.984:
  E/AndroidRuntime(2334): FATAL EXCEPTION: main 07-01 15:33:02.984:
  E/AndroidRuntime(2334): java.lang.RuntimeException: Unable to instantiate activity
  ComponentInfo{com.example.myfirstapp/com.example.myfirstapp.MainActivity}:
  java.lang.NullPointerException 07-01 15:33:02.984:
  E/AndroidRuntime(2334): at  android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
  07-01 15:33:02.984: E/AndroidRuntime(2334): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
  07-01 15:33:02.984: E/AndroidRuntime(2334): at android.app.ActivityThread.access$600(ActivityThread.java:130) 07-01
  15:33:02.984: E/AndroidRuntime(2334): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
  07-01 15:33:02.984: E/AndroidRuntime(2334): at android.os.Handler.dispatchMessage(Handler.java:99) 07-01
  15:33:02.984: E/AndroidRuntime(2334): at android.os.Looper.loop(Looper.java:137) 07-01 15:33:02.984:
  E/AndroidRuntime(2334): at android.app.ActivityThread.main(ActivityThread.java:4745) 07-01
  15:33:02.984: E/AndroidRuntime(2334): at java.lang.reflect.Method.invokeNative(Native Method) 07-01
  15:33:02.984: E/AndroidRuntime(2334): at java.lang.reflect.Method.invoke(Method.java:511) 07-01 15:33:02.984:
  E/AndroidRuntime(2334): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
  07-01 15:33:02.984: E/AndroidRuntime(2334): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 07-01
  15:33:02.984: E/AndroidRuntime(2334): at dalvik.system.NativeStart.main(Native Method) 07-01 15:33:02.984:
  E/AndroidRuntime(2334): Caused by: java.lang.NullPointerException
  07-01 15:33:02.984: E/AndroidRuntime(2334): at android.app.Activity.findViewById(Activity.java:1825) 07-01
  15:33:02.984: E/AndroidRuntime(2334): at com.example.myfirstapp.MainActivity.&lt;init&gt;(MainActivity.java:28) 07-01
  15:33:02.984: E/AndroidRuntime(2334): at java.lang.Class.newInstanceImpl(Native Method) 07-01 15:33:02.984:
  E/AndroidRuntime(2334): at java.lang.Class.newInstance(Class.java:1319) 07-01 15:33:02.984:
  E/AndroidRuntime(2334): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
  07-01 15:33:02.984: E/AndroidRuntime(2334): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
  07-01 15:33:02.984: E/AndroidRuntime(2334):     ... 11 more
  </code></pre>
  
  <p>When attempting to use the <strong>findViewById</strong>, this error comes up referring to line 28.</p>
  
  <p>The program looks like the following:</p>
  
  <pre><code>package com.example.myfirstapp;
  
  import android.app.Activity;
  import android.os.Bundle;
  import android.view.Menu;
  import android.view.View;
  import android.view.View.OnClickListener;
  import android.widget.Button;
  import android.widget.TextView;
  
  public class MainActivity extends Activity implements OnClickListener{
  
      int a = 0;
  
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
      }
  
      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
      }
  
  
      Button button1 = (Button) findViewById(R.id.button1);
      TextView topLeft = (TextView) findViewById(R.id.textView2);
  //  button1.setOnClickListener( this );
  
      public void onClick(View v) {
          // TODO Auto-generated method stub
  
      }    
  
  }
  </code></pre>
  
  <p>What does this mean? Why is my code having trouble doing something along the lines of referring to the R.java file?</p>
  
  <pre><code>R.java does have
      public static final class id {
          public static final int button1=0x7f080001;
          public static final int menu_settings=0x7f080003;
          public static final int textView1=0x7f080000;
          public static final int textView2=0x7f080002;
  </code></pre>
  
  <p>Thanks in advance.</p>