[JAVA] JAVA에서의 형변환(casting)

 

 

 

 

 

 

 

 

1. 문자 -> 숫자

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1. String -> Int
   

   String testA = "12345";
   int testB = Integer.parseInt(testA);

   
   
   
2. String -> Double, Float 
   

   //String -> Double
   String testA = "10";
   double testB = Double.valueOf(testA);
   
   //String -> Float
   String testA = "10";
   float testB = Float.valueOf(testA);
   ​

   
   
   
   
   

 

 

 

 

2. 숫자 -> 문자

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1. Int-> String 
   

   int testA = 12356;
   String testB = Integer.toString(testA);

   
   
   
   
   
   
2. Double, Float  -> String
   

   //1번방식 => String.valueOf(Float값,Double값)
   //2번방식 => Float.toString(Float값,Double값)
   
   float testF = 10.10;
   double testD = 10.10;
   		
   String testS;
   
   testS = String.valueOf(testF); //Float -> String (1번방식)
   testS = Float.toString(testF); //Float -> String (2번방식)
   		
   testS = String.valueOf(testD); //Double -> String (1번방식)
   testS = Double.toString(testD); //Double -> String (2번방식)

   
   
   
    

 

 

 

 

3. 정수 <->  실수

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1. Double, Float -> Int
   

   //(int)실수값
   double testD = 10.101010;
   float testF = 10.1010
   
   int testI;
   testI = (int)testD; //Double-> Int
   testI = (int)testF; //Float -> Int​

   
   
   
   
2. Int -> Double, Float
   

   //(int)실수값
   int testI = 10;
   	
   double testD = (double)testI; //Int -> Double
   float testF = (float)testI; //Int -> Float​

   
   
   
   
   

 

 

4. 기타

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1. String -> Date(문자 -> 날짜)
   

   String testA = "2021-12-23 11:11:11";
   
   //testA의 날짜 형식과 동일하게 맞춰줍니다.
   //2021-12-23 11:11:11 -> yyyy-MM-dd HH:mm:ss
   SimpleDateFormat fm = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
   
   Date testB = fm.parse(testA);​

   
   
   
   
2. String -> JSON
   

   //1. Json 문자열
   String strJson = "{\"playerName\":\"son\", "
   + "\"playerNum\":\"7\","
   + "\"playerInfo\":{"
   + "\"age\":30,"
   + "\"foot\":\"right\""
   + "}"
   + "}";
   
   //2. Parser
   JSONParser jsonParser = new JSONParser();
   
   //3. To Object
   Object obj = jsonParser.parse(strJson);
   
   //4. To JsonObject
   JSONObject jsonObj = (JSONObject) obj;
   
   //print
   System.out.println(jsonObj.get("playerName")); //son
   System.out.println(jsonObj.get("playerNum")); //7
   System.out.println(jsonObj.get("playerInfo")); // {"age":30,"foot":"right"}​