Map Interface - collection

https://wikidocs.net/208 기본개념 

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Key를 통해 value를 얻는다.

Part of the collctions framework(not a true collection(->data save))

Each key는 only map to a sinlge value (-> 동일 key에 다른 value값 add하면, @overwritten됨.)

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map.put(key, value) ;   add     

                        ----> sout(map.put(key, vlaue)); 는 출력오류남. 미리 add하고 sout(map.get(key)); 로 써야함.

map.get(key);  출력

map.containkey(key);  검색

map.remove();  제거

           ........... ex)map.remve(key);   or   map.remove(key, vlaue)   or map.remove(key,oldvalue,newvalue);

                                                              해당 key,value 값이 맞아야 제거됨.

map.size(); 갯수 return

keySet  : setting된 key값들

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LinkedHashMap: 입력순 출력/  TreeMaP : sort순

예)

Map<String, String> abd = new HashMap<>();

         key,    value

abd.put(key, value);

 

예시)

package com.timbuchalka;

import java.util.HashMap;
import java.util.Map;

public class MapProgram {

    public static void main(String[] args) {
        Map<String, String> languages = new HashMap<>();	// V
        if(languages.containsKey("Java")) {                 //  V
            System.out.println("Java already exists");
        } else {
            languages.put("Java", "a compiled high level, object-oriented, platform independent language");
            System.out.println("Java added successfully");
        }
         //         V
        languages.put("Python", "an interpreted, object-oriented, high-level programming language with dynamic semantics");
        languages.put("Algol", "an algorithmic language");
        System.out.println(languages.put("BASIC", "Beginners All Purposes Symbolic Instruction Code"));	//출력오류
        System.out.println(languages.put("Lisp", "Therein lies madness"));  //출력오류: add먼저 후 sout(object.get())써야함.

        if(languages.containsKey("Java")) {                // V
            System.out.println("Java is already in the map");
        } else {
            languages.put("Java", "this course is about Java");
        }

        System.out.println("================================================");

        for(String key: languages.keySet()) {                // V
            System.out.println(key + " : " + languages.get(key));
        }
    }
}

Output

D:\IT\JDK\jdk11.0.6_10\bin\java.exe "-javaagent:D:\IT\IDEA\IntelliJ IDEA Community Edition 2020.1\lib\idea_rt.jar=50422:D:\IT\IDEA\IntelliJ IDEA Community Edition 2020.1\bin" -Dfile.encoding=UTF-8 -classpath D:\IT\Java-Collections-Maps-Source-code\out\production\Collections com.timbuchalka.MapProgram
Java added successfully
null
null
Java is already in the map
================================================
Java : a compiled high level, object-oriented, platform independent language
BASIC : Beginners All Purposes Symbolic Instruction Code
Lisp : Therein lies madness
Python : an interpreted, object-oriented, high-level programming language with dynamic semantics
Algol : an algorithmic language

Process finished with exit code 0