Gentle Introduction to Prototypes and Prototypal Inheritance in Javascript

In this short video tutorial I will explain in simple terms what are prototypes in Javascript and how Inheritance works.

Key points to keep in mind

  • In Javascript if an object wants to inherit from another object then it can do so using prototypal inheritance.
  • The parent object is referred to as Prototype.
  • __proto__ is deprecated, we can use Object.create()
let fourWheelerObj = {tyres: 4} // Prototype

let carObjectOne = {engine: 'v6', __proto__: fourWheelerObj}

console.log(carObjectOne.tyres) // 4


let carObjectTwo = Object.create(fourWheelerObj)
console.log(carObjectTwo.tyres) // 4

Learn about Javascript Strings

We will learn how to create Strings, escaping quotes and string concatenation.

Code examples below are also available at Github

Creating a String
Strings are surrounded by quotation marks. It can be single or double quotes.
Just like we declare and initialize numbers we can work with strings.

let message = 'Hello World';
message

Here message is a string literal.

Escaping Characters in a String
Let’s say we need to use the following string – 'I'm at the store right now'. As you can see here we have a single quote in the string itself. This won’t work.
To handle this we can use the \ symbol.
let message = 'I\'m at the store right now'
Using \’ solves the problem.

Joining two strings
To join or concatenate two strings we can use + operator.
let str1 = 'Hello';
let str2 = 'Sam';

str1+' '+str2

To convert a string to a number you can use the Number() function.
To convert a number to a string you can use toString()

Example
let numStr = '922';
typeof(numStr)

let num = Number(numStr);
typeof(num)

let tempStr = num.toString();
typeof(tempStr)

Template Literals or Template Strings
This is a new addition. Using this it’s convenient to concatenate strings or print out a variable value.
We use backtick instead of quotes.
let fName = 'Raj';
let message = Check this out. My name is ${fName};
message

Learn how to create different versions of your App like Free and Paid

Android framework makes it quite easy for you to generate different flavors and variants of your App. Like you can create a free version or a paid version of your App.

In order to do this you need to follow these steps:

You need to specify the variants or flavors in your App’s build.gradle file.

Like

productFlavors {
    demo {
        applicationId "com.edocent.demo"
        versionName "1.0-demo"
    }
    full {
        applicationId "com.edocent.full"
        versionName "1.0-full"
    }
}

In all likelihood your Free App version will need a different Activity compared to the Paid one. So you need to create different folders for the two flavors.

So go to the Project->src folder and create a new Java Folder – free.

Create another one for paid similarly.

Add appropriate Activity and other files to this folder.

And you are all set. Execute Generate Signed APK task from the Build option. This will ask you which flavor you need the APK for.

Cool isn’t it.

Source code is available here

Learn how to generate a signed APK file

All Android Apps must be digitally signed before they are installed on a device.

This is required to verify identity of developer who published it. And also to verify if it has been tampered.

Follow the video to generate the signed APK file and also to learn how to automate the process.

 

Learn how to create and use a Android Module in your Android Project

You saw why using modules is important and how to create a Java module in an earlier Post. In a similar fashion you can add an Android module to your project.

Android Studio makes it easy to add a new module. Follow the video to understand the steps.

Source code is available here

What is Android Debug Bridge or ADB ?

An ADB is a command line tool which can be used to communicate with Emulator or Android Devices.

When your development machine needs to communicate with an Android Device it does so using ADB. It’s a process that is controlled by a command also known as adb.

The adb command works by talking to an adb server which runs in the background at port 5037. The server is also known as adb daemon or adbd.

Android Studio also talks to this server when it needs to run an app via an Android Device.

To work with ADB you need Android SDK.

Learn how to create and use a Java Module in Android Project

Creating modules is a good practice since it aids in reusability. In your Android project you can easily add a Java or Android module.

Follow the video to create a Java module and add it as a dependency in your Android Project.

Project source code is available in GitHub

Android Basics – Learn how the APK file Works in Android

Once you have transferred an APK file to your Android device its stored in /data/app/<package-name>

The classes.dex file is extracted from it and it’s converted to native library, when the App is run the first time, and stored in /data/dalvik-cache. This Machine Code can be run by the CPU.

Each Android device runs a process called Zygote. When an App needs to run Zygote creates a forked version of itself. Which means its a process in memory. Using this forked process and by loading the native library the App can be loaded pretty quickly.

Android Basics – Understanding Android Run Time, Dalvik and APK

If you are familiar with the Java Virtual Machine(JVM) then you will know that a JVM works on class files which are comprised of byte code. A class file is a compiled version of the Java code.

When it comes to Android then the Java code is first compiled to a class file which in turn is converted to a file called classes.dex –¬†Dalvik Executable format. This is done by a tool called dx

Like JVM in Android’s case its Dalvik which works on the dex file.

A JVM is stack based processor whereas Dalvik is register based. Both are virtual processors though.

The classes.dex file is then compressed with a bunch of other files, like resource and data files, into a ZIP file called an Application Package or APK

This is the file you will eventually upload to the Google Play Store.