Question

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.

public class SampleActivity extends Activity {

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);
}

log cat

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

Answer 1

You need to initialize octet before you can start assigning values to its elements. Change your declaration to:

int octet[] = new int[4];

Alternatively, add this line:

octet = new int[4];

to generatingRandomIpAddress() before you start assigning to the elements of octet.

P.S. In the future, when you are asking for help with an exception, you should post the logcat output showing the stack trace for the exception.