GitHub Wiki - Yash-777/LearnJava GitHub Wiki

Task lists

- [x] #739
- [ ] Add delight to the experience when all tasks are complete :tada:
  • #739
  • Add delight to the experience when all tasks are complete 🎉

Using emojis

@octocat :+1: This PR looks great - it's ready to merge! :shipit:

@octocat 👍 This PR looks great - it's ready to merge! :shipit:

Alerts

> [!NOTE]
> Useful information that users should know, even when skimming content.

> [!TIP]
> Helpful advice for doing things better or more easily.

> [!IMPORTANT]
> Key information users need to know to achieve their goal.

> [!WARNING]
> Urgent info that needs immediate user attention to avoid problems.

> [!CAUTION]
> Advises about risks or negative outcomes of certain actions.

Note

Useful information that users should know, even when skimming content.

Tip

Helpful advice for doing things better or more easily.

Important

Key information users need to know to achieve their goal.

Warning

Urgent info that needs immediate user attention to avoid problems.

Caution

Advises about risks or negative outcomes of certain actions.

Tables

Single line code

Code Information
String s = "Yash"; String literal 
<table>
  <tr>
    <th>Header 1</th>
    <th>Header 2</th>
  </tr>

<tr>
<td><pre><code>

Java code

</code></pre></td>
<td>

<img src="https://user-images.githubusercontent.com/17373064/224510169-6b318147-4bb0-4cb3-a7b4-a180502d21b9.png" alt="image">

</td>
</tr>

</table>

Multi-Line Code

Stream Stream in Detail oracle article 

List transactionsIds = 
    transactions.stream()
                .filter(t -> t.getType() == Transaction.GROCERY)
                .sorted(comparing(Transaction::getValue).reversed())
                .map(Transaction::getId)
                .collect(toList());
image

Example Collapsible Content

A collapsible section with markdown

Click to expand!

Heading

  1. A numbered
  2. list
    • With some
    • Sub bullets

NB: Make sure you have an empty line after the closing tag, otherwise the markdown/code blocks won't show correctly.

Click to expand! 
function logSometing(something) {
   console.log(`Logging: ${something}`);
}
Click to close! - Already open... 
function logSometing(something) {
   console.log(`Logging: ${something}`);
}

Show Some Code then Expand

Click to see more:
Given the following python code 
from pychartjs import BaseChart

class myChart(BaseChart):
    pass
chartJSON = myChart().get()
Write the following HTML
<div class="container">
   <canvas id="myChart"></canvas>
</div>
... and JS
var data = {{ chartJSON | safe }}
var ctx = document.getElementById("myChart").getContext('2d');
var myChart = new Chart(ctx, data);

In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behavior.

Method signature: It consists of method name and parameter list (number/type/order of the parameters). methodName(parametersList y). An instance method in a subclass with the same signature and return type as an instance method in the super-class overrides the super-class's method.

Java OOP concepts
Class  - Collection of a common features of a group of object [static/instance Fields, blocks and Methods]
Object - Instance of a class (instance fields)
Abstraction - Process of hiding complex info and providing required info like API, Marker Interfaces ...
Encapsulation(Security) - Class Binding up with data members(fields) and member functions.
Inheritance  (Reusability by placing common code in single class)
 1. Multilevel - {A -> B -> C} 2. Multiple - Diamond problem {A <- (B) -> C} [Java not supports] 3. Cyclic {A <-> B} [Java not supports]
 * Is-A   Relation - Class A extends B
 * Hash-A Relation - Class A { B obj = new B(); } - (Composition/Aggregation)
Polymorphism (Flexibility) 1. Compile-Time Overloading    2. Runtime Overriding  [Greek - "many forms"]


int[] arr = {1,2,3}; int arrLength = arr.length;   // Fixed length of sequential blocks to hold same data type
String str = "Yash"; int strLength = str.length(); // Immutable Object value can't be changed.

List<?> collections = new ArrayList<String>(); int collectionGroupSize = collections.size();
Map<?, ?> mapEntry = new HashMap<String, String>();
Set<?> keySet = mapEntry.keySet(); // Set of Key's
Set<?> entrySet = mapEntry.entrySet(); // Set of Entries [Key, Value]

// Immutable Objects once created they can't be modified. final class Integer/String/Employee
Integer val = Integer.valueOf("100"); String str2 = String.valueOf(100); // Immutable classes
final class Employee { // All Wrapper classes, java.util.UUID, java.io.File ...
    private final String empName; // Field as Final(values can be assigned only once) Only getter functions.
    public Employee(String name) { this.empName = name; }
}

Native Java Code for Hashtable.h, Hashtable.cpp SQL API.

You can check your current JDK and JRE versions on your command prompt respectively,

  • JDK javac -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/p: javac 1.8.0_121
  • JRE java -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/P: java version "1.8.0_102"

JAVA_HOME - Must be set to JDK otherwise maven projects leads to compilation error. [ERROR] No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK? C:\Softwares\OpenJDK\, 7-zip

Fatal error compiling: invalid target release: JRE and JDK must be of same version 1.8.0.XXX

Disable TLS 1.0 and 1.1security-libs/javax.net.ssl: TLS 1.0 and 1.1 are versions of the TLS protocol that are no longer considered secure and have been superseded by more secure and modern versions (TLS 1.2 and 1.3).

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