Ошибки в классе Activity

Прохожу курс по Android, возникли проблемы с выполнение задания.

Нужно сделать простой светофор, по нажатию кнопки - меняется фон.

Вот main.class:

package com.example.opimand.oneswitchsemofor;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
    private final RelativeLayout mRealtiveLayout=(RelativeLayout) findViewById(R.id.activity_main);
    private final TextView mTextView=(TextView) findViewById(R.id.textView);
    Button redButoom=(Button) findViewById(R.id.buttonRed);
    Button yellowButtom= (Button) findViewById(R.id.buttonRed);
    Button greenButtom= (Button) findViewById(R.id.buttonGreen);
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.buttonRed:
                mTextView.setText(R.string.red);
                mRealtiveLayout.setBackgroundColor(ContextCompat.getColor(MainActivity.this,R.color.colorRed));
                break;
            case R.id.buttonYellow:
                mTextView.setText(R.string.yellow);
                mRealtiveLayout.setBackgroundColor(ContextCompat.getColor(MainActivity.this,R.color.colorYellow));
                break;
            case R.id.buttonGreen:
                mTextView.setText(R.string.green);
                mRealtiveLayout.setBackgroundColor(ContextCompat.getColor(MainActivity.this,R.color.colorGreen));
        }
    }
}

А вот main.xml:

<?xml version="1.0" encoding="utf-8"?>
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello Kitty!"
    android:id="@+id/textView" />
<Button
    android:text="@string/green"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/textView"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="148dp"
    android:id="@+id/buttonGreen"
    android:onClick="onClick"/>
<Button
    android:text="@string/yellow"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/buttonGreen"
    android:layout_alignRight="@+id/buttonGreen"
    android:layout_alignEnd="@+id/buttonGreen"
    android:layout_marginTop="17dp"
    android:id="@+id/buttonYellow"
    android:onClick="onClick"/>
<Button
    android:text="@string/red"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="13dp"
    android:id="@+id/buttonRed"
    android:onClick="onClick"
    android:layout_below="@+id/buttonYellow"
    android:layout_alignLeft="@+id/buttonYellow"
    android:layout_alignStart="@+id/buttonYellow" />