Java
/
Basics
- 1 Basics 9
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Classes
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Objects
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Arrays
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Variables
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Loops
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Numbers
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Strings
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Exceptions
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Regexp
- 2 OOP 9
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Inheritance
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Polymorphism
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Static
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Abstract
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Interfaces
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Constructors
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Packages
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Nested Classes
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Final
- 3 Compiler 2
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Sublime Text
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Apache Ant
- 4 Collections 8
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Lists
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Comparable
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Sets
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Maps
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Generics
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Properties
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Streams
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Json
- 5 Threads 4
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Create Thread
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Sleep
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Lock
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Scheduler
- 6 Design patterns 4
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Singleton
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Observer
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Strategy
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Mediator
- 7 Swing 12
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Frame
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Panel
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Listener
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Combo Box
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Label
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Image
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Menu
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Table
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Layout
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Drawing
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Timer
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Designer
- 8 I/O 7
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Streams IO
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Socket
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Watching Files
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Mail
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Logger
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Clipboard
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Encrypt
- 9 Effective 7
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Constructors
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Dependency Injection
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Composition
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Interfaces Default
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Import Static
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Enums
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Lambdas
- 10 Junit 5
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About Junit
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Test Case
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Suite Test
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Annotations
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Exceptions
- 11 Lambdas 7
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Expressions
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Functional Interfaces
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Streams
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Common Operations
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Default Methods
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Static Methods
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Single Responsibility
- 12 JavaFX 6
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Openjfx
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Scene Builder
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First App
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Jar Archive
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On Action
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Change Listener
- 13 Maven 4
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Demo
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Spring Boot
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Junit
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Guava
- 14 Spring Boot 8
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Quick start
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Rest service
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Consuming Rest
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Templates
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Security
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Command Line
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Scheduling Tasks
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Ajax
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Numbers
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Last update: 29-10-2021
Numbers
! Java provides wrapper classes for each primitive data types.
/**
* All of the numberic wrapper classes are subclasses of ...
* the abstract class Number.
*
* Effective Java (Item 49):
* Prefer primitive types to boxed primitives.
*/
package com.minte9.basics.numbers;
public class Numbers {
public static void main(String[] args) {
Number no = Double.valueOf(22.33);
System.out.println(no.shortValue()); // 22
}
}
Autoboxing
! Java compiler makes automatic convertions to primitives and vice-versa.
/**
* Primitives types cannot be used in Collections or Generics.
* Java compiler makes automatic convertions to primitives.
*
* Unboxing is the automatic conversion of objects into their ...
* coresponding primitives
*/
package com.minte9.basics.numbers;
import java.util.List;
import java.util.ArrayList;
public class Autoboxing {
public static void main(String[] args) {
List<Integer> li = new ArrayList<>();
for (int i=10; i<20; i++) {
li.add(i);
// autoboxing (i is primitive)
}
System.out.println(li.get(0).getClass().getName());
// java.lang.Integer
int b = li.get(0);
// unboxing (element is Integer)
System.out.println(b);
// 10
}
}
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