MainActivity.java

package com.example.android.justjava;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;

import java.text.NumberFormat;

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

    int quantity = 2;

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

    /**
     * This method is called when the order button is clicked.
     */
    public void submitOrder(View view) {
        int totalPrice = calculatePrice(quantity);
        String summary = createOrderSummary(totalPrice);
        displayMessage(summary);
    }

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

    /**
     * This method is called when the order button is clicked.
     */
    public void decrement(View view) {
        if (quantity > 0) {
            quantity = quantity - 1;
            display(quantity);
        }
    }

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

    /**
     * Calculates the price of the order.
     *
     * @param quantity is the number of cups of coffee ordered
     */
    private int calculatePrice(int quantity) {
        int price = quantity * 5;
        return price;
    }
    
    /**
     * Creates the order summary.
     * 
     * @param price is the total order price
     */
    private String createOrderSummary(int price) {
        String summary = "Name: Kapitain Boris";
        summary += "\nQuantity: " + quantity;
        summary += "\nTotal: $" + price;
        summary += "\nThank you!";
        
        return summary;
    }
}