Dark Mode Light Mode Android Example Java

Step 1/  For night mode Go to Values>Themes> themes.xml / Night and create styles

<style name="Screen_background">
    <item name="android:background">#000000</item>
</style>

<style name="Screen_Text">
    <item name="android:textColor">#FFFFFF</item>
</style>

<style name="Screen_button">
    <item name="android:textColor">#FFFFFF</item>
    <item name="android:background">@color/design_default_color_primary_dark</item>
</style>

<style name="Screen_surface">
    <item name="android:background">#121212</item>
</style>

Step 2/  For Light Mode

<style name="Screen_background">
    <item name="android:background">#FFFFFF</item>
</style>

<style name="Screen_Text">
    <item name="android:textColor">#000000</item>
</style>

<style name="Screen_button">
    <item name="android:textColor">#FFFFFF</item>
    <item name="android:background">@color/design_default_color_primary</item>
</style>

<style name="Screen_surface">
    <item name="android:background">#E7E6E6</item>
</style>

Step 3/  XML - Design

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    style="@style/Screen_background"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Switch
        android:id="@+id/modeSwitcher"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

    <TextView
        android:id="@+id/textView"
        style="@style/Screen_Text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="Light &amp; Dark Mode"
        android:textSize="24dp"
        app:layout_constraintBottom_toTopOf="@+id/linearLayout"
        app:layout_constraintTop_toTopOf="parent" />

    <LinearLayout
        android:layout_marginBottom="70dp"
        android:id="@+id/linearLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent">

        <View
            style="@style/Screen_surface"
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:layout_marginEnd="10dp" />

        <View
            style="@style/Screen_surface"
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:layout_marginEnd="10dp" />

        <View
            style="@style/Screen_surface"
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:layout_marginEnd="10dp" />

        <View
            style="@style/Screen_surface"
            android:layout_width="80dp"
            android:layout_height="100dp"
            android:layout_marginEnd="10dp" />

    </LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

Step 4/ MainActivity. Used SharedPreferances to save the mode for further 

package com.tutorialb.darkmodelightmode;

import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.widget.Switch;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.app.AppCompatDelegate;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

public class MainActivity extends AppCompatActivity {

    Switch aSwitch;
    SharedPreferences sharedPreferences;
    SharedPreferences.Editor editor;
    boolean isNightMode;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        aSwitch = findViewById(R.id.modeSwitcher);
        sharedPreferences = getSharedPreferences("MODE", Context.MODE_PRIVATE);
        isNightMode = sharedPreferences.getBoolean("night", false);

        if (isNightMode){
            aSwitch.setChecked(true);
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
        }

        aSwitch.setOnClickListener(v -> {
            if (isNightMode){
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
                editor = sharedPreferences.edit();
                editor.putBoolean("night", false);
            }

            else {
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
                editor = sharedPreferences.edit();
                editor.putBoolean("night", true);
            }
            editor.apply();
        });


    }
}

Step 5:  Output