ExampleHandlerThread

activity_main.xml

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toTopOf="@+id/startThreadButton"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.593" />

    <Button
        android:id="@+id/startThreadButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="startThread"
        android:text="startThread"
        app:layout_constraintBottom_toTopOf="@+id/stopThreadButton"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/taskFooButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="executeTaskFoo"
        android:text="taskFoo"
        app:layout_constraintBottom_toTopOf="@+id/taskBarButton"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/stopThreadButton" />

    <Button
        android:id="@+id/taskBarButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="executeTaskBar"
        android:text="taskBar"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/taskFooButton" />

    <Button
        android:id="@+id/stopThreadButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="stopThread"
        android:text="stopThread"
        app:layout_constraintBottom_toTopOf="@+id/taskFooButton"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/startThreadButton" />

</androidx.constraintlayout.widget.ConstraintLayout>

ExampleHandlerThread.java

package com.example.handlerthread;

import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.util.Log;

public class ExampleHandlerThread extends HandlerThread {

    private static final String TAG = "ExampleLooperThread";

    public Handler handler;
    public Looper looper;

    public ExampleHandlerThread() {
        super("ExampleLooperThread");
    }

    @Override
    public void run() {
        Log.d(TAG, "run() called");

        Looper.prepare();

        looper = Looper.myLooper();

        handler = new Handler(Looper.getMainLooper());

        Looper.loop();
    }
}

MainActivity.java

package com.example.handlerthread;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.View;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";

    private final ExampleHandlerThread handlerThread = new ExampleHandlerThread();
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void startThread(View view) {
        Log.d(TAG, "startThread() called");
        handlerThread.start();
    }

    public void stopThread(View view) {
        Log.d(TAG, "stopThread() called");
        handlerThread.looper.quit();
    }

    public void executeTaskFoo(View view) {
        Log.d(TAG, "executeTaskFoo() called");
        Handler fooThreadHandler = new Handler(handlerThread.looper);
        fooThreadHandler.post(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 5; i++) {
                    Log.d(TAG, "executeTaskFoo: " + i);
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                }

                Log.d(TAG, "executeTaskFoo: run: ended");
            }
        });
    }

    public void executeTaskBar(View view) {
        Log.d(TAG, "executeTaskBar() called");
        Handler barThreadHandler = new Handler(handlerThread.looper);
        barThreadHandler.post(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 3; i++) {
                    Log.d(TAG, "executeTaskBar: " + i);
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                }

                Log.d(TAG, "executeTaskFoo: run: ended");
            }
        });
    }
}