How to set background color of an android activity to yellow Programatically?

This example demonstrates how do I set background color of an android activity to yellow programmatically.

Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.

Step 2 − Add the following code to res/layout/activity_main.xml.

<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:id="@+id/relativeLayout"
   tools:context=".MainActivity">
   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerInParent="true"
      android:textStyle="bold"
      android:textSize="24sp"
      android:text="The color of the Activity is Yellow"/>
</RelativeLayout>

Step 3 − Add the following code to src/MainActivity.java

import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.RelativeLayout;
public class MainActivity extends AppCompatActivity {
   RelativeLayout relativeLayout;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      relativeLayout = findViewById(R.id.relativeLayout);
      relativeLayout.setBackgroundColor(Color.YELLOW);
   }
}

Step 4 - Add the following code to androidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="app.com.sample">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen –

Click here to download the project code.