<Java> Map , HashMap

Java에서 Map 은 키-값 쌍 으로 데이터를 저장하는데 사용되는 인터페이스이다. 

HashMap 은 Map 인터페이스의 구현 클래스 이다. 

Java에는 데이터를 키-값 쌍에 저장하기 위해Map인터페이스를 구현하는 여러 클래스 (TreeHashMap,LinkedHashMap)가 있습니다. 


<<<Java의HashMap클래스>>>

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

public class workathomeTest{ 
    public static void main(String[] args) {
        
		Map<String, Integer> workIn = new HashMap<>();
        workIn.put("One", 1);
        workIn.put("Two", 2);
        workIn.put("Three", 3);
       
       System.out.println(workIn);
	   //출력 
	   // {One=1, Two=2, Three=3}
	   
	   Map<String, Integer> workOut = new TreeMap<>(workIn);
       System.out.println(workOut);
    
	}
}

 

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

public class workathomeTest{ 
    public static void main(String[] args) {
        
Map<String, Integer> workIn = new HashMap<>();
        workIn.put("One", 1);
        workIn.put("Two", 2);
        workIn.put("Three", 3);
       
       System.out.println(workIn);
   //출력 
   // {One=1, Two=2, Three=3}
    
	}
}

Map은 인터페이스이므로HashMap,TreeMap등과 같은 구현 클래스의 참조를 보유하는 데 사용할 수 있습니다.
Map인터페이스에TreeMap또는HashMap오브젝트를 보유 할 수 있습니다.

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

public class workathomeTest{ 
    public static void main(String[] args) {
        
	Map<String, Integer> workIn = new HashMap<>();
        workIn.put("One", 1);
        workIn.put("Two", 2);
        workIn.put("Three", 3);
       
       System.out.println(workIn);
       //출력 
       // {One=1, Two=2, Three=3}
   
	  Map<String, Integer> workOut = new TreeMap<>(workIn);
       System.out.println(workOut);
    
	}
}