【 Android Development for Beginners】 Lesson 3A : Object Oriented Programming - 2

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Android Development for Beginners

Lesson 3A : Object Oriented Programming

Output from a method

If you want to output from a method : return value is the key point.

Review









A method has a return data type
and there will need the return message

to return the value to the upper layer-----UI

The word write behind the return data can't be reachable because the declaration were done in  "return message".

If there is no need to use return value, the method return data type is void.


Use Return Value


Define and Call a Method


 The displayMessage Method - Quiz

First Step


Second Step

	package com.example.android.justjava;
	import android.os.Bundle;
	import android.support.v7.app.ActionBarActivity;
	import android.view.View;
	import android.widget.TextView;
	/**
	* This app displays an order form to order coffee.
	*/
	public class MainActivity extends ActionBarActivity {
	int quantity = 1;
	@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 price = calculatePrice();
	displayMessage(createOrderSummary());
	}
	/**
	* Calculates the price of the order.
	*
	* @return total price
	*/
	private int calculatePrice() {
	int price = quantity * 5;
	return price;
	}
	/**
	* Create summary of the order.
	*
	*
	* @return text "order"
	*/
	private String createOrderSummary(){
	int price = quantity * 5;
	String order = "Name: Kaptain Kunal" + "\nQuantity: " + quantity + "\nTotal: " + price + "\nthank you";
	return order;
	}
	/**
	* This method is called when the increment button is clicked.
	*/
	public void increment(View view) {
	quantity = quantity + 1;
	displayQuantity(quantity);
	}
	/**
	* This method is called when the decrement button is clicked.
	*/
	public void decrement(View view) {
	quantity = quantity - 1;
	displayQuantity(quantity);
	}
	/**
	* This method displays the given quantity value on the screen.
	*/
	private void displayQuantity(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 orderSummaryTextView = (TextView) findViewById(R.id.order_summary_text_view);
	orderSummaryTextView.setText(message);
	}
	}

view raw Object Oriented Programming2.java hosted with ❤ by GitHub

	<?xml version="1.0" encoding="utf-8"?>
	<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
	xmlns:tools="http://schemas.android.com/tools"
	android:layout_width="match_parent"
	android:layout_height="match_parent"
	android:orientation="vertical"
	android:paddingBottom="@dimen/activity_vertical_margin"
	android:paddingLeft="@dimen/activity_horizontal_margin"
	android:paddingRight="@dimen/activity_horizontal_margin"
	android:paddingTop="@dimen/activity_vertical_margin"
	tools:context="com.example.android.justjava.MainActivity">
	<TextView
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:layout_marginBottom="16dp"
	android:text="Quantity"
	android:textAllCaps="true" />
	<LinearLayout
	android:layout_width="match_parent"
	android:layout_height="wrap_content"
	android:orientation="horizontal"
	android:layout_marginBottom="16dp">
	<Button
	android:layout_width="48dp"
	android:layout_height="48dp"
	android:onClick="decrement"
	android:text="-" />
	<TextView
	android:id="@+id/quantity_text_view"
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:paddingLeft="8dp"
	android:paddingRight="8dp"
	android:text="1"
	android:textColor="@android:color/black"
	android:textSize="16sp" />
	<Button
	android:layout_width="48dp"
	android:layout_height="48dp"
	android:onClick="increment"
	android:text="+" />
	</LinearLayout>
	<TextView
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:layout_marginBottom="16dp"
	android:text="Order Summary"
	android:textAllCaps="true" />
	<TextView
	android:id="@+id/order_summary_text_view"
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:layout_marginBottom="16dp"
	android:text="$5 "
	android:textColor="@android:color/black"
	android:textSize="16sp" />
	<Button
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:onClick="submitOrder"
	android:text="order" />
	</LinearLayout>

view raw Object Oriented Programming2.xml hosted with ❤ by GitHub