<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    tools:context=".MainActivity">
    <TextClock
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:format12Hour="MM/dd/yy h:mmaa"/>
    <TextClock
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:format12Hour="MMM dd, yyyy h:mmaa"/>
    <TextClock
        android:id="@+id/timeTextClock"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:format12Hour="MMMM dd, yyyy h:mm:aa"/>
    <TextClock
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:format12Hour="E, MMMM dd, yyyy h:mmaa"/>
    <TextClock
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:format12Hour="EEEE, MMMM dd, yyyy h:mmaa"/>
 
    <Button
        android:id="@+id/setTimeButton"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Button" />
</LinearLayout>

package org.mk.android.demo.demotxtclock;
 
import androidx.appcompat.app.AppCompatActivity;
 
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextClock;
 
public class MainActivity extends AppCompatActivity {
    private TextClock timeClock;
    private Button setTimeButton;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setTimeButton = (Button) findViewById(R.id.setTimeButton);
        timeClock = (TextClock) findViewById(R.id.timeTextClock);
        setTimeButton.setOnClickListener(new OnClickListener());
    }
 
    private class OnClickListener implements View.OnClickListener {
        @Override
        public void onClick(View v) {
            String clockFormatter = "MMMM dd, yyyy h:mm:ss";
            if (timeClock.is24HourModeEnabled()) {
                Log.i("app", ">>>>>>System has been enabled the 24Hour Model");
                timeClock.setFormat24Hour(clockFormatter);
            } else {
                Log.i("app", ">>>>>>System has not been enabled the 24Hour " +
                        "Model");
                timeClock.setFormat12Hour(clockFormatter);
            }
        }
    }
}