JAVA - ynjch97/YNJCH_WIKI GitHub Wiki

โ–ท instanceof

  • System.out.println(a instanceof A);
  • true, false ํƒ€์ž…์œผ๋กœ ๋ฐ˜ํ™˜
  • ๋ถ€๋ชจ ๊ฐ์ฒด์—ฌ๋„ true ๋ฐ˜ํ™˜

โ–ท Enumeration

  • ๋ฉ”์†Œ๋“œ
    • hasMoreElements(์š”์†Œ๊ฐ€ ์žˆ์œผ๋ฉด true, ์•„๋‹ˆ๋ฉด false ๋ฐ˜ํ™˜)
    • nextElement(๋‹ค์Œ ์š”์†Œ๋ฅผ ๋ฐ˜ํ™˜)
  • ์˜ˆ์‹œ
java.util.Enumeration < ? > enumeration = null ;
enumeration = request.getSession ( ).getAttributeNames ( ) ;
while ( enumeration.hasMoreElements ( ) ) {
	keyStr = enumeration.nextElement ( ).toString ( ) ;
}
hashMap.put ( keyStr , request.getParameter ( keyStr ) ) ;

โ–ท Model, ModelMap

  • ๋‘˜ ๋‹ค addAttribute๋ฅผ ์‚ฌ์šฉํ•จ
  • ๋ฐ์ดํ„ฐ๋งŒ ์ €์žฅ ํ›„ View์—์„œ ์‚ฌ์šฉํ•˜๊ธฐ ์œ„ํ•ด ์“ฐ์ž„
  • Model ์€ ์ธํ„ฐํŽ˜์ด์Šค, ModelMap ์€ ํด๋ž˜์Šค๋ผ๋Š” ์ฐจ์ด์ ์ด ์žˆ์Œ
model.addAttribute("๋ณ€์ˆ˜๋ช…");
modelMap.addAttribute("๋ณ€์ˆ˜๋ช…");

โ–ท ModelAndView

  • addObject๋ฅผ ํ†ตํ•ด ๋ฐ์ดํ„ฐ๋ฅผ ์ €์žฅ
  • setViewName์„ ํ†ตํ•ด ์ด๋™ํ•˜๊ณ ์ž ํ•˜๋Š” View๋ฅผ ์ €์žฅ
  • return type ModelAndView
ModelAndView mv = new ModelAndView(); 
mv.addObject("modelAndViewVar", modelAndViewStr);
mv.setViewName("temp/test");
return mv;

โ–ท Enum ์‚ฌ์šฉ

  • ์‹คํ–‰ ๊ฒฐ๊ณผ ๋ฆฌํ„ด ์‹œ Enum ์‚ฌ์šฉ ์˜ˆ์ œ
// ํด๋ž˜์Šค ์ƒ์„ฑ
public class ResultVO {

	public ResultVO() {
	}
	
	public ResultVO(ResultStatus result) {
		setResult(result);
	}

	protected ResultStatus result;
	protected String resultMsg;
	protected boolean isSuccess;
	
	public ResultStatus getResult() {
		return result;
	}
	public void setResult(ResultStatus result) {
		this.result = result;
		isSuccess = (ResultStatus.SUCCESS == this.result);
	}
	public String getresultMsg() {
		return resultMsg;
	}
	public void setresultMsg(String resultMsg) {
		this.resultMsg = resultMsg;
	}
	public boolean getIsSuccess() {
		return isSuccess;
	}
	
	public enum ResultStatus {
		SUCCESS,
		FAIL
	}
}
int result = testMapper.insertTest(testVo);
if (result == 1) {
	return new ResultVO(ResultStatus.SUCCESS);
} else {
	return new ResultVO(ResultStatus.FAIL);
}

โ–ท map ์ „์ฒด ์ถœ๋ ฅํ•˜๊ธฐ

  • key ์™€ value ๋‘ ๊ฐœ ๋ชจ๋‘๊ฐ€ ํ•„์š”ํ•  ๊ฒฝ์šฐ : entrySet()
  • key ๊ฐ’๋งŒ ํ•„์š”ํ•  ๊ฒฝ์šฐ : keySet()
  • Iterator() ๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ๋ฐฉ๋ฒ• 3, 4์™€ ๊ฐ™์ด ์‚ฌ์šฉํ•ด๋„ ๋จ
// ๋ฐฉ๋ฒ• 01 : entrySet()
for (Map.Entry<String, String> entry : map.entrySet()) {
	System.out.println("[key]:" + entry.getKey() + ", [value]:" + entry.getValue());
}

// ๋ฐฉ๋ฒ• 02 : keySet()
for (String key : map.keySet()) {
	String value = map.get(key);
	System.out.println("[key]:" + key + ", [value]:" + value);
}

// ๋ฐฉ๋ฒ• 03 : entrySet().iterator()
Iterator<Map.Entry<String, String>> iteratorE = map.entrySet().iterator();
while (iteratorE.hasNext()) {
	Map.Entry<String, String> entry = (Map.Entry<String, String>) iteratorE.next();
	String key = entry.getKey();
	String value = entry.getValue();
	System.out.println("[key]:" + key + ", [value]:" + value);
}

// ๋ฐฉ๋ฒ• 04 : keySet().iterator()
Iterator<String> iteratorK = map.keySet().iterator();
while (iteratorK.hasNext()) {
	String key = iteratorK.next();
	String value = map.get(key);
	System.out.println("[key]:" + key + ", [value]:" + value);
}

โ–ท HashMap ๊ด€๋ จ ํ•จ์ˆ˜

clear() HashMap์— ์ €์žฅ๋œ ๋ชจ๋“  ๊ฐ์ฒด๋ฅผ ์ œ๊ฑฐ
clone() ํ˜„์žฌ HashMap์„ ๋ณต์ œํ•˜์—ฌ ๋ฐ˜ํ™˜
map.clear();
newmap = (HashMap)map.clone();

โ–ท Queue

  • PriorityQueue : ์šฐ์„ ์ˆœ์œ„ ํ(๋„ฃ์€ ์ˆœ์„œ๊ฐ€ ์•„๋‹Œ ๊ฐ’์˜ ์ˆœ์„œ๋Œ€๋กœ ์ถœ๋ ฅ๋จ)
PriorityQueue<Integer> q = new PriorityQueue<Integer>();
PriorityQueue<Integer> q = new PriorityQueue<Integer>(Collections.reverseOrder()); // ์—ญ์ˆœ ์ถœ๋ ฅ
  • Queue ์กฐ์ž‘
Queue<Integer> queue = new LinkedList<>();
queue.offer(1); // ๊ฐ’ ๋„ฃ๊ธฐ 
queue.add(1); // ๊ฐ’ ๋„ฃ๊ธฐ (offer์™€ ๋‹ฌ๋ฆฌ ํ๊ฐ€ ๊ฝ‰ ์ฐจ์„œ ์ถ”๊ฐ€ํ•  ์ˆ˜ ์—†๋Š” ๊ฒฝ์šฐ์—๋Š” ์—๋Ÿฌ๊ฐ€ ์ถœ๋ ฅ)
queue.poll(); // ๊ฐ’ ๋นผ๊ธฐ
queue.remove(); // ๋‹ค์Œ์— ์ถœ๋ ฅ๋  ๊ฐ’์„ ์ง€์›€
queue.peek(); // ๋‹ค์Œ์— ์ถœ๋ ฅ๋  ๊ฐ’์„ ํ™•์ธ
queue.element(); // ๋‹ค์Œ์— ์ถœ๋ ฅ๋  ๊ฐ’์„ ํ™•์ธ (peek๊ณผ ๋‹ฌ๋ฆฌ Queue์—์„œ ๋‹ค ๋ฝ‘์•„๋‚ด๊ฑฐ๋‚˜ Queue๊ฐ€ ๋น„์–ด์žˆ์œผ๋ฉด ์—๋Ÿฌ๊ฐ€ ์ถœ๋ ฅ)
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