Android Project 1: Intro

Intro to Java / Kotlin

Every Class is going to be a Story!

Evolution

Java / Kotlin

Converted to ⬇️

Binary (0s and 1s)

Early days of Programming till 1950s

0100 1001 0001 0000

This instruction tells the computer to add the contents of memory location 1 to the contents of memory location 0 and store the result in memory location 2.

ADD 1,0,2
0100 1001 0001 0000

This instruction tells the computer to add the contents of memory location 1 to the contents of memory location 0 and store the result in memory location 2.

Machine Language

Assembly Language

Year Event
1946 The first electronic digital computer, the Electronic Numerical Integrator and Computer (ENIAC), is built. It is programmed using machine language.
1950s Assembly language is developed.
1960s High-level programming languages are developed, such as FORTRAN and COBOL. These languages are easier to use than assembly language, but they are not as efficient.
1970s The microprocessor is invented. This makes it possible to build smaller and more affordable computers.
1980s Personal computers become popular. Assembly language is still used for some low-level programming tasks, but high-level languages are becoming more common.
1990s The internet becomes popular. This leads to the development of new programming languages, such as Java and Python.
2000s Cloud computing and mobile computing become popular. This leads to the development of new programming languages, such as Swift and Kotlin.
2020s The development of artificial intelligence and machine learning is driving the development of new programming languages.

Trend 

More Code to Less Code

Hello World



class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}
https://www.programiz.com/java-programming/online-compiler/
object Driver {
@JvmStatic
    fun main(args: Array<String>) {
     println("Hello World")
    
    }
    
 }

Important Concepts

Important Concepts

Primitive Data Types

 

Int

Char

String

Primitive Data Types

 

Int

Char

String

Array

Problem: 

 

Harder to store data in just Primitive Data Types

Solution

1. Creating Objects using Primite Data Types

 

Object {

name: "Harnoor"

age: 25

DOB: "12/12/2000"

}

 

 

 

Objects

Hold data

 

Employee empl1 = new Employee("Harry", 25,1947))

Employee empl1 = new Employee("Harry", 25,1947))

Static keyword Significance

These variables are shared among all instances (objects) of the class

Static keyword Significance

example:
static final double PI = 3.14159;

in Kotlin-> 
val PI: Double = 3.14159

1. saves memory

2. Usage -> Class.staticname

3. one value and consisten

Python vs Java

# hello.py

print("Hello, World!")
python3 hello.py

Python vs Java

# hello.py

print("Hello, World!")
 

# hello.py

print("Hello, World!")
 

java ->

 

javac file.java

java file 

builds the compile code (Whole unit gets run vs line by line)

Kotlin vs Java

Which is faster?

Java or Kotlin?

Answer: We need both as both compile to JVM and Kotlin and Java are used interchangeable
Java / Kotlin

⬇️

JVM

Byte Code: 0s or 1s

Slow Down Harnoor

Reminding myself

Why Object in Kotlin?

Class can have one driver

  1. Object -> executed when program starts
  2. No Constructor
  3. Static-Like Behavior

Keywords in Java

for, while, class, private etc

cannot be used as variable / class / object Names

Inheritance

  • Don't reinvent the wheel
  • Parent -> Child class
  • Child is become meta class (meta means more than before)
  • So easy to add features

Encapsulation

Encapsulation

code looks clean when can be accessed by

object.function()

 

as you know the operations possible easily

Polymorphism

Object having multiple forms

Employee employee1 = new Contractor("John", "Contractor", 123);
Employee employee2 = new Intern("Smith", "Full Time", 456);
Employee employee3 = new FullTime("Sara", "Intern", 789);

Declarative vs Imperative

SQL vs Java

SELECT * FROM customers WHERE state = 'CA';

public String getCustomers() {
	return "Customer1"
}

Java Objects


Employee employee1 = new Employee("Harnoor",25,"12/12/2000")

Problem:

    public static void printEmployeeSalary(Employee employee){
        if (employee.employeeType.equals("Contractor")) {
            System.out.println("Contractor Salary: $100,000");
        } else if (employee.employeeType.equals("Full Time")) {
            System.out.println("Full Time Salary: $150,000");
        } else if (employee.employeeType.equals("Intern")) {
            System.out.println("Intern Salary: $50,000");
        }
    }

Let's Implement together 2 mins break

Solution of Messy If statements / Switch

Object Oriened Programming:

1. Inheritance

2. Polymorphism

3. Abstraction

Refer: Week 1 repo

github.com/iHarnoor/Week1Android

Homework Discussion

Reviewing PR

Android Revision (week2)

Constraint Layout

ImageView

Button Click 

Compile-Time vs Run-Time Error

Which is Better?

lateinit var vs null object


 

Initialization Property is uninitialized until explicitly initialized using lateinit. Property is initialized to null by default.
Nullable Property No need for a ? after the property type, as it's not nullable. Property is implicitly nullable (requires ? after the property type).
Null Safety Risky if not properly initialized; accessing an uninitialized lateinit property will result in a runtime exception. Safe by default, as properties are initialized to null. Null checks or safe calls (?.) are required when accessing.
Initialization Responsibility Developer must ensure that the property is initialized before use. No obligation to explicitly initialize the property; it can remain null.
Use Cases - Used when you can guarantee that the property will be initialized before being accessed. - To avoid nullable types and null checks, especially for properties that are expected to always have a value. - Used when there's a possibility that the property might not be initialized immediately or can be left as null intentionally. - When you need to handle null values explicitly.

without Lamda

public class Main {
    public static void main(String[] args) {
        Adder adder = new Adder();
        int result = adder.add(5, 7);
        System.out.println("Result of adding 5 and 7 is: " + result);
    }
}

class Adder {
    public int add(int a, int b) {
        return a + b;
    }
}

fun main() {
    val add: (Int, Int) -> Int = { a, b -> a + b }

    val result = add(5, 7)
    println("Result of adding 5 and 7 is: $result")
}

with Lamda in Kotlin

ImageView and set Image in Android

1. Which is faster to share Image: Base64 or Downloading?

2. Why use Glide?

Using Library: Glide

1. Never reinvent wheel

2. Use Documentations

3. Gradle import

 

https://github.com/bumptech/glide

Add Permission

Add internet permisson

  I  Root cause (1 of 1)
java.lang.SecurityException: Permission denied (missing INTERNET permission?)
at java.net.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:150)
at java.net.Inet6AddressImpl.lookupAllHostAddr(Inet6AddressImpl.java:103)
at java.net.InetAddress.getAllByName(InetAddress.java:1152)
at com.android.okhttp.Dns$1.lookup(Dns.java:41)
at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:178)
at com.android.okhttp.internal.http.RouteSelector.nextProxy(Ro

Trick of the Day

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