Java
/
OOP
- 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
/
Constructors
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Last update: 17-06-2022
Constructors
p 241 Every class you create has a constructor, even if you don't write one.
/**
* Constructor use the class name and has no return type.
* You could have more than one constructor in a class.
*/
package com.minte9.oop.constructors;
public class Constructors {
public static void main(String[] args) {
new A().test();
new B("aaa");
new B(100);
/*
Default constructor used
Constructor 1 - aaa
Constructor 2 - 100
*/
}
}
class A {
/*
public Output() {
// default constructor
}
*/
public void test() {
System.out.println("Default constructor used");
}
}
class B {
public B(String s) {
System.out.println("Constructor 1 - " + s);
}
public B(int i) {
System.out.println("Constructor 2 - " + i);
}
}
This
p 256 To call another constructor from the same class use this() method.
/**
* To call another constructor from the same class ...
* use this() method.
*/
package com.minte9.oop.constructors;
public class This {
public static void main(String[] args) {
Rectangle a = new Rectangle();
Rectangle b = new Rectangle(100, 200);
Rectangle c = new Rectangle(300, 400, 11, 22); // Look Here
System.out.println(a);
System.out.println(b);
System.out.println(c);
/*
W: 0 H: 0 x: 0 y: 0
W: 100 H: 200 x: 0 y: 0
W: 300 H: 400 x: 11 y: 22
*/
}
}
class Rectangle {
private int x, y;
private int width, height;
public Rectangle() {
this(0, 0, 0, 0); // Look Here
}
public Rectangle(int width, int height) {
this.width = width;
this.height = height;
}
public Rectangle(int width, int height, int x, int y) {
this(width, height);
this.x = x;
this.y = y;
}
public String toString() {
return String.format(
"W: %s H: %s x: %s y: %s", width, height, x, y
);
}
}
➥ Questions github OOP