title: Calculator in Android_Beginner level
body: <p>I have just started coding in Android.
  I made an attempt to create an app that will calculate sum of two numbers.
  Getting errors even in this simple program.
  Application shows:
  Unfortunately application_name has stopped, when running in emulator.</p>
  
  <pre><code>package com.example.first;
  
  import org.w3c.dom.Text;
  
  
  import android.R.string;
  import android.os.Bundle;
  import android.app.Activity;
  import android.content.DialogInterface;
  import android.content.DialogInterface.OnClickListener;
  import android.view.Menu;
  import android.view.View;
  import android.widget.Button;
  import android.widget.EditText;
  import android.widget.TextView;
  
  public class MainActivity extends Activity implements android.view.View.OnClickListener
  {
      Button buttonSum,buttonSumOne;
      EditText textOne,textTwo;
      TextView textSum;
      float a,b,sum;
      @Override
      public void onCreate(Bundle savedInstanceState)
      {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          buttonSum=(Button)findViewById(R.id.button1);
          buttonSum.setOnClickListener(this);
          textOne=(EditText)findViewById(R.id.editText1);
          textTwo=(EditText)findViewById(R.id.editText2);
          textSum=(TextView)findViewById(R.id.textSum);
          a=Float.parseFloat(textOne.getText().toString());
          a=Float.valueOf(textOne.getText().toString());
          b=Float.parseFloat(textTwo.getText().toString());
          sum=a+b;
      }
  
      @Override
      public boolean onCreateOptionsMenu(Menu menu) 
      {
          // Inflate the menu; this adds items to the action bar if it is present.
          getMenuInflater().inflate(R.menu.activity_main, menu);
          return true;
      }
  
      @Override
      public void onClick(View v) {
          // TODO Auto-generated method stub
          if(R.id.button1==v.getId())         
              textSum.setText(String.valueOf(sum));
  
      }
  
  
  }
  </code></pre>
  
  <p>Logcat:</p>
  
  <pre><code>03-16 07:08:16.297: W/Trace(791): Unexpected value from nativeGetEnabledTags: 0
  03-16 07:08:16.316: W/Trace(791): Unexpected value from nativeGetEnabledTags: 0
  03-16 07:08:18.496: D/AndroidRuntime(791): Shutting down VM
  03-16 07:08:18.496: W/dalvikvm(791): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
  03-16 07:08:18.536: E/AndroidRuntime(791): FATAL EXCEPTION: main
  03-16 07:08:18.536: E/AndroidRuntime(791): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.first/com.example.first.MainActivity}: java.lang.NumberFormatException: Invalid float: ""
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.os.Handler.dispatchMessage(Handler.java:99)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.os.Looper.loop(Looper.java:137)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.app.ActivityThread.main(ActivityThread.java:5039)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at java.lang.reflect.Method.invokeNative(Native Method)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at java.lang.reflect.Method.invoke(Method.java:511)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at dalvik.system.NativeStart.main(Native Method)
  03-16 07:08:18.536: E/AndroidRuntime(791): Caused by: java.lang.NumberFormatException: Invalid float: ""
  03-16 07:08:18.536: E/AndroidRuntime(791):  at java.lang.StringToReal.invalidReal(StringToReal.java:63)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at java.lang.StringToReal.parseFloat(StringToReal.java:289)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at java.lang.Float.parseFloat(Float.java:300)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at com.example.first.MainActivity.onCreate(MainActivity.java:33)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.app.Activity.performCreate(Activity.java:5104)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
  03-16 07:08:18.536: E/AndroidRuntime(791):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
  03-16 07:08:18.536: E/AndroidRuntime(791):  ... 11 more
  03-16 07:08:52.026: I/Process(791): Sending signal. PID: 791 SIG: 9
  </code></pre>