My app doesn't open and force closes
<p>My app force closes as soon as I open it,
this is my first app, and i have tried to find errors but i can't
I have attached log cat since starting this app:</p>

<pre><code>          12-03 16:04:54.040: W/dalvikvm(8798): threadid=1: thread exiting with uncaught exception (group=0x40018578)
          12-03 16:04:54.040: E/AndroidRuntime(8798): FATAL EXCEPTION: main
          12-03 16:04:54.040: E/AndroidRuntime(8798): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sditya.quadratic.equation/com.sditya.quadratic.equation.Quadratic}: java.lang.NullPointerException
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at android.app.ActivityThread.access$1500(ActivityThread.java:117)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at android.os.Handler.dispatchMessage(Handler.java:99)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at android.os.Looper.loop(Looper.java:130)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at android.app.ActivityThread.main(ActivityThread.java:3687)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at java.lang.reflect.Method.invokeNative(Native Method)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at java.lang.reflect.Method.invoke(Method.java:507)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at dalvik.system.NativeStart.main(Native Method)
          12-03 16:04:54.040: E/AndroidRuntime(8798): Caused by: java.lang.NullPointerException
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at com.sditya.quadratic.equation.Quadratic.initialize(Quadratic.java:58)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at com.sditya.quadratic.equation.Quadratic.onCreate(Quadratic.java:24)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
          12-03 16:04:54.040: E/AndroidRuntime(8798):   ... 11 more
</code></pre>

<p>and XML layout of the main activity that starts on first:</p>

<pre><code>&lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="20dp" &gt;

&lt;TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Co-efficient of x.square" /&gt;

&lt;EditText
    android:id="@+id/editText1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:hint="Co-efficient of x.square" /&gt;

&lt;TextView
    android:id="@+id/textView2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Co-efficient of x" /&gt;

&lt;EditText
    android:id="@+id/editText2"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:hint="Co-efficient of x" /&gt;

&lt;TextView
    android:id="@+id/textView3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Constant Term" /&gt;

&lt;EditText
    android:id="@+id/editText3"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:hint="Constant Term" /&gt;

&lt;Button
    android:id="@+id/button1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Button" /&gt;

&lt;TextView
    android:id="@+id/tvResults"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:gravity="center"
    android:text="TextView" /&gt;
</code></pre>

<p></p>

<p>The <strong>initialize</strong> method:</p>

<pre><code>private void initialize() { 
// TODO Auto-generated method stub
tr = (TextView) findViewById(R.id.tvResults); 
xs = (EditText) findViewById(R.id.editText1);
x = (EditText) findViewById(R.id.editText2); 
c = (EditText) findViewById(R.id.editText3); 
b.setOnClickListener(this); 
} 
</code></pre>
