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
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Regexp S
- 2 OOP 9
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Inheritance
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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
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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
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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 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
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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 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
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Lambdas
- 10 Junit 5
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About Junit S
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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 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
HashMap
Each element in a Map is actually two objects, a key and a value.
/**
* In a HashMap you can have duplicate values ...
* but no duplicate keys.
*/
package com.minte9.collections.maps;
import java.util.HashMap;
public class Hashmaps {
public static void main(String[] args) {
HashMap<String, Integer> scores =
new HashMap<String, Integer>();
scores.put("a", 1);
scores.put("a", 2); // overrites "a" key
scores.put("b", 2);
scores.put("c", 2);
System.out.println(scores); // {a=2, b=2, c=2}
System.out.println(
scores.get("a") // 2
);
}
}
Loop
If you only need the values, use for loop and values().
/**
* To parse a HashMap use for loop with ...
*
* keySet(), if you need only the keys,
* values(), if you need only the values,
* entrySet(), if you need both.
*/
package com.minte9.collections.maps;
import java.util.HashMap;
import java.util.Map;
public class Loops {
public static void main(String[] args) {
HashMap<String, Integer> scores =
new HashMap<String, Integer>();
scores.put("a", 1);
scores.put("b", 2);
scores.put("c", 3);
for (String key : scores.keySet()) {
System.out.println(key);
// a b c
}
for(Object value : scores.values()) {
System.out.println(value);
// 1 2 3
}
for(Map.Entry<String, Integer> entry : scores.entrySet()) {
String key = entry.getKey();
Integer value = entry.getValue();
System.out.println(key + value);
// a1 b2 c3
}
}
}
➥ Questions
Last update: 293 days ago