无法从Java程序中引用的main.xml获取小部件

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent"
              android:background="@color/white">
  <TextView android:layout_width="fill_parent" 
            android:layout_height="wrap_content" 
            android:text="@string/hello"/>
  <TextView android:text="Heading Text" 
            android:id="@+id/TextView01" 
            android:layout_width="wrap_content" 
            android:layout_height="wrap_content">
  </TextView>
  <Button android:text="Button Text" 
          android:id="@+id/Button01" 
          android:layout_width="wrap_content" 
          android:layout_height="wrap_content">
  </Button>
</LinearLayout>

Java程序是

import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;


public class TestButton extends Activity {

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Button myButton = (Button)findViewById(android.R.id.Button01);

    }
}

“Button”行上的错误是：
Button01无法解析或不是字段

任何想法,我做的是什么非常基本的错误:( :(.