Java
/
Collections
- 1 Basics 9
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Classes S
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Objects S
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Arrays S
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Variables S
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Loops S
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Numbers S
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Strings S
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Exceptions S
-
Regexp S
- 2 OOP 9
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Inheritance
-
Polymorphism
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Static S
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Abstract
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Interfaces
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Constructors S
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Packages
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Nested Classes
-
Final
- 3 Compiler 2
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Sublime Text S
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Apache Ant
- 4 Collections 8
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Lists
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Comparable S
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Sets
-
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 S
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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
-
Drawing
-
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
-
Logger
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Clipboard
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Encrypt S
- 9 Effective 7
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Constructors S
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Dependency Injection
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Composition
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Interfaces Default
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Import Static S
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Enums
-
Lambdas
- 10 Junit 5
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About Junit S
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Test Case
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Suite Test
-
Annotations
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Exceptions
- 11 Lambdas 7
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Expressions S
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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 S
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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 13
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Quick start S
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Rest service S
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Consuming rest S
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Templates S
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Security auth S
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Command line S
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Scheduled task S
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Ajax S
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Jdbc mysql S
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Encrypt password S
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Https S
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Jwt S
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Post request S
R
Q
Type
There is nothing particulary complex about the concept of generic types.
/**
* A generic type is a special kind of variable ...
* with whatever type you pass in.
*/
package com.minte9.collections.generics;
public class Type {
public static void main(String[] args) {
A a = new A();
a.set(10);
System.out.println(a.get()); // 10
a.set("John");
System.out.println(a.get()); // John
Box<Integer> b = new Box<>();
b.set(10);
System.out.println(b.get()); // 10
// b.set("John"); // Error: not applicable ...
}
}
class A { // non generic class
private Object obj;
public void set(Object o) {
obj = o;
}
public Object get() {
return obj;
}
}
class Box<T> { // generic class (type)
private T t;
public void set(T t) {
this.t = t;
}
public T get() {
return t;
}
}
Multiple
You can use multiple generic type parameters.
/**
* A generic type may have multiple type parameters.
* Each parameter must be unique.
*/
package com.minte9.collections.generics;
public class Multiple {
public static void main(String[] args) {
Box<Integer, Integer> box = new Box<>();
box.set(10);
System.out.println(box.get()); // 10
}
static class Box<T, U> {
private T t;
public void set(T t) {
this.t = t;
}
public T get() {
return t;
}
}
// static class Word<T, T> {} // Error: Duplicate type parameter T
}
Limitations
Generics types cannot be static (or used with primitives).
/**
* Generic type params can't be static.
*
* Because static field is shared by all objects ...
* what's the actual type of t?
*
* Generics cannot be used with primitives.
*/
package com.minte9.collections.generics;
public class Limitations {
public static void main(String[] args) {
Box<Integer> b1 = new Box<>();
Box<String> b2 = new Box<>();
System.out.println(b1.hashCode());
System.out.println(b2.hashCode());
// Box<int> box = new Box<int>(); // not allowed!
}
static class Box<T> {
//static T t; // Error: static reference to non-static T
}
}
➥ Questions