<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"     android:paddingLeft="@dimen/activity_horizontal_margin"     android:paddingRight="@dimen/activity_horizontal_margin"     android:paddingTop="@dimen/activity_vertical_margin"     tools:context=".MainActivity" >     <TextView         android:id="@+id/showWord"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignLeft="@+id/GreenBtn"         android:layout_alignParentTop="true"         android:layout_alignRight="@+id/BlueBtn"         android:layout_marginTop="17dp"         android:text="@string/ShowWordText"         android:textStyle="bold" />     <Button         android:id="@+id/GreenBtn"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignParentLeft="true"         android:layout_below="@+id/showWord"         android:layout_marginLeft="22dp"         android:layout_marginTop="28dp"         android:gravity="left|center_vertical|center_horizontal"         android:text="@string/GreenBtnText" />     <Button         android:id="@+id/BlueBtn"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignBaseline="@+id/YellowBtn"         android:layout_alignBottom="@+id/YellowBtn"         android:layout_toRightOf="@+id/YellowBtn"         android:gravity="left|center_vertical|center_horizontal"         android:text="@string/BlueBtnText" />     <Button         android:id="@+id/YellowBtn"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignBaseline="@+id/GreenBtn"         android:layout_alignBottom="@+id/GreenBtn"         android:layout_toRightOf="@+id/GreenBtn"         android:gravity="left|center_vertical|center_horizontal"         android:text="@string/YellowBtnText" /> </RelativeLayout>

package com.example.demo1; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView; import android.app.Activity; import android.graphics.Color;   public class MainActivity extends Activity implements OnClickListener{     TextView tv_show=null;     Button greenBtn=null;     Button blueBtn=null;     Button yellowBtn=null;     @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         tv_show=(TextView)findViewById(R.id.showWord);         greenBtn=(Button)findViewById(R.id.GreenBtn);         blueBtn=(Button)findViewById(R.id.BlueBtn);         yellowBtn=(Button)findViewById(R.id.YellowBtn);         greenBtn.setOnClickListener(this);         blueBtn.setOnClickListener(this);         yellowBtn.setOnClickListener(this);     }     @Override     public void onClick(View v) {     switch (v.getId()) {     case R.id.GreenBtn:         tv_show.setTextColor(Color.GREEN);                break;     case R.id.BlueBtn:         tv_show.setTextColor(Color.BLUE);                break;     case R.id.YellowBtn:         tv_show.setTextColor(Color.YELLOW);                break;     default:         break;     }     } }