why my android app force close
<p>i will put my code in the description. the code is to solve the Pythagorean theorem</p>

<pre><code>  package com.example;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class PythagoreantheoremActivity&lt;textField&gt; extends Activity {
    /** Called when the activity is first created. */
    EditText field1;
    EditText field2;
    TextView text1;
    String num1;
    String num2;
    String RAnswer;
    double num3;
    double num4;
    double num5;
    double num6;
    double fnum;
    double snum;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Button button1 = (Button) findViewById(R.id.button1);
        field1 = (EditText) findViewById(R.id.tf1);
        text1 = (TextView) findViewById(R.id.text1);
        field2 = (EditText) findViewById(R.id.tf2);
        button1.setOnClickListener(new View.OnClickListener() {
            @Override   
            public void onClick(View v) {       
                text1.setText(RAnswer);
                double fnum = Double.parseDouble(num1);
                double snum = Double.parseDouble(num2);
                String RAnswer = Double.toString(num6);
                num2 = field1.toString();
                num1 = field2.toString();
                num3 = fnum * fnum;
                num4 = snum * snum; 
                num5 = num4 + num3;
                num6 = sqrt(num5);
            }

            private double sqrt(double num5) {
                // TODO Auto-generated method stub
                return num6;
            }
        });
}

}
</code></pre>

<p>here is my manifestcode</p>

<pre><code> &lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.example"
      android:versionCode="1"
      android:versionName="1.0"&gt;
    &lt;uses-sdk android:minSdkVersion="4" /&gt;
    &lt;application android:icon="@drawable/icon" android:label="@string/app_name"&gt;
        &lt;activity android:name=".TheoremappActivity"
                  android:label="@string/app_name"&gt;
            &lt;intent-filter&gt;
                &lt;action android:name="android.intent.action.MAIN" /&gt;
                &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
            &lt;/intent-filter&gt;
        &lt;/activity&gt;
    &lt;/application&gt;
&lt;/manifest&gt;
</code></pre>
