Android: findViewbyID undefined

I'm a beginner on Android programming, and get stuck when following the code from a book. I checked another threads but I couldn't find a solution. Hope you can help me.

My code:

karmind_test.java

package karmind.com.karmind_test;

import android.app.Activity;
import android.os.Bundle;
import android.content.Intent;
import android.view.View;
import android.view.View.OnClickListener;

public class Karmind_test extends Activity开发者_如何学运维 implements OnClickListener {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);    

    // Set up click listeners for all the buttons
    View about_button = findViewbyID(R.id.about_button);
    about_button.setOnClickListener(this);

    View exit_button = findViewbyID(R.id.exit_button);
    exit_button.setOnClickListener(this);

    }

    public void onClick(View v) {
        switch (v.getId()) {
        case R.id.about_button:
            Intent i = new Intent(this, About.class);
            startActivity(i);
            break;
        // More buttons here
        }
    }
}

main.xml

<LinearLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
        android:background="@color/background"
        android:orientation="horizontal"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:padding="30dip">
    <LinearLayout 
    android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center">
    <TextView
    android:text="@string/menu"
    android:textSize="24.5sp"
    android:layout_gravity="center"
    android:layout_marginBottom="25dip"
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content"/> 
    <Button  
        android:id= "@+id/about_button"
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        android:text="@string/about"/>
    <Button  
        android:id= "@+id/exit_button"
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        android:text="@string/exit"/>
    <TextView
    android:text="@string/copyright"
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content"/> 
    </LinearLayout>
</LinearLayout>

The error I got twice:

The method findViewbyID(int) is undefined for the type Karmind_test

Thanks for helping me out.

---

Java is case sensitive. The method name is findViewById, not findViewByID.