Week 2 Class 2

Android: Java / Kotlin Basics

Homework Discussion

Reviewing PR

Goal of Today

Types of Classes in Kotlin

1. data class -> OOPs

2. object class

3. Library vs Framework?

4. Android App UI -> Image set with a button

What is a class?

1. Blueprint or a Template to create objects 2. Classes encapsulate data for the object

 

What is a class?

Solution of Messy If statements / Switch

Object Oriened Programming:

1. Inheritance

2. Polymorphism

3. Abstraction

Refer: Week 1 repo

github.com/iHarnoor/Week1Android

Converting Java code to a library

Step Java Kotlin
1. Compile Source Code javac YourJavaFile.java kotlinc YourKotlinFile.kt -include-runtime -d YourOutputJar.jar
2. Create Manifest (Optional) Create MANIFEST.MF Create MANIFEST.MF
3. Package into JAR jar cvf YourLibrary.jar -C /path/to/compiled/classes . jar cvf YourLibrary.jar -C /path/to/compiled/classes .
4. Include Manifest (Optional) jar cvfm YourLibrary.jar MANIFEST.MF -C /path/to/compiled/classes . jar cvfm YourLibrary.jar MANIFEST.MF -C /path/to/compiled/classes .
5. Verify the JAR jar tf YourLibrary.jar jar tf YourLibrary.jar

Library vs Framework?

Android Revision (week2)

Constraint Layout

ImageView

Button Click 

Compile-Time vs Run-Time Error

Which is Better?

Compile-Time vs Run-Time Error

 

println("Hello, world!"

 

 

a = 10 b = 0 result = a / b # Division by zero error (ZeroDivisionError)

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

Declarative vs Imperative

SQL vs Java

SELECT * FROM customers WHERE state = 'CA';

public String getCustomers() {
	return "Customer1"
}

Week 2 Class 2: Kotlin Basics + Creating our First App (RestAPI + GLide

By Harnoor Singh

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Week 2 Class 2: Kotlin Basics + Creating our First App (RestAPI + GLide

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