Just java app Lesson 2 MainActivity .java file....

 package com.example.justjava;

import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

/**
 * This app displays an order form to order coffee.
 */
public class MainActivity extends AppCompatActivity {

    int quantity = 0;

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

    // This method is increment method and this is called when + button is clicked.
    public void increment(View view) {
        quantity = quantity + 1;
        display(quantity);
    }

    // This method is decrement method and this is called when - button is clicked.
    public void decrement(View view) {
        if (quantity > 1) {
            quantity = quantity - 1;
            display(quantity);
        }
    }

    /**
     * This method is called when the order button is clicked.
     */
    public void submitOrder(View view) {
        String priceMessage ="Price: $" + quantity*5 + "\n";
        priceMessage = priceMessage + "Thank You!";
        displayMessage(priceMessage);
    }

    /**
     * This method displays the given quantity value on the screen.
     */
    private void display(int number) {
        TextView quantityTextView = (TextView) findViewById(R.id.quantity_text_view);
        quantityTextView.setText("" + number);

    }

    /**
     * This method displays the given price on the screen.
     */
//    private void displayPrice(int number) {
//        TextView priceTextView = (TextView) findViewById(R.id.price_text_view);
//        priceTextView.setText(NumberFormat.getCurrencyInstance().format(number));
//}

    /**
     * This method displays the given text on the screen.
     */
    private void displayMessage(String message) {
        TextView priceTextView = (TextView) findViewById(R.id.price_text_view);
        priceTextView.setText(message);
    }
}