title: where to set nullpointerexception
body: <p>im very new in developing an android app.. when i run my program in the emulator it force close.. i figure it out that i need to set an nullpointerexception but i dont know where to set those stuff.. pls help me. </p>
  
  <p>public class SampleActivity extends Activity {</p>
  
  <pre><code>TextView dp_octet1, dp_octet2, dp_octet3, dp_octet4, dp_slashes;
  int i = 0;
  int j = 0;
  int octet[];
  
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_sample);
      iniTextView();
      generatingRandomIpAddress();
  }
  
  private void generatingRandomIpAddress() {
  
  
     Random i = new Random();           //Random number between 0-2
     if(i.nextInt(3)==0){
         octet[0] = 8+(i.nextInt(22));
         octet[1] = 1+(i.nextInt(126));
     }
     if(i.nextInt(3)==1){
         octet[0] = 16+(i.nextInt(14));
         octet[1] = 128+(i.nextInt(63));
     }
     if(i.nextInt(3)==2){
         octet[0] = 24+(i.nextInt(6));
         octet[1] = 192+(i.nextInt(31));
     }
     octet[2] = (i.nextInt(255));
     octet[3] = (i.nextInt(255));
     octet[4] = (i.nextInt(255));
  
     //Display the problem
     dp_slashes.setText(octet[0]);
     dp_octet1.setText(octet[1]);
     dp_octet2.setText(octet[2]);
     dp_octet3.setText(octet[3]);
     dp_octet4.setText(octet[4]);
  
  }
  
  
  
  private void iniTextView() {
      // TODO Auto-generated method stub
      dp_octet1 = (TextView) findViewById(R.id.octet1);
      dp_octet2 = (TextView) findViewById(R.id.octet2);
      dp_octet3 = (TextView) findViewById(R.id.octet3);
      dp_octet4 = (TextView) findViewById(R.id.octet4);
      dp_slashes = (TextView) findViewById(R.id.slashes);
  }
  </code></pre>
  
  <p>log cat</p>
  
  <p>08-05 09:11:07.180: D/AndroidRuntime(1286): Shutting down VM
  08-05 09:11:07.180: W/dalvikvm(1286): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
  08-05 09:11:07.203: E/AndroidRuntime(1286): FATAL EXCEPTION: main
  08-05 09:11:07.203: E/AndroidRuntime(1286): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myscratches/com.example.myscratches.SampleActivity}: java.lang.ArrayIndexOutOfBoundsException
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at android.os.Handler.dispatchMessage(Handler.java:99)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at android.os.Looper.loop(Looper.java:123)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at android.app.ActivityThread.main(ActivityThread.java:4627)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at java.lang.reflect.Method.invokeNative(Native Method)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at java.lang.reflect.Method.invoke(Method.java:521)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at dalvik.system.NativeStart.main(Native Method)
  08-05 09:11:07.203: E/AndroidRuntime(1286): Caused by: java.lang.ArrayIndexOutOfBoundsException
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at com.example.myscratches.SampleActivity.generatingRandomIpAddress(SampleActivity.java:32)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at com.example.myscratches.SampleActivity.onCreate(SampleActivity.java:24)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
  08-05 09:11:07.203: E/AndroidRuntime(1286):     ... 11 more</p>