Stack & Queue

class stack => last in first out , LIFO , push/pop, ArrayList

 

|           2            |        => pop

|            1           |

|             0          |

|____________ |

 

interface queue => first in first out, FIFO, offer/poll/peek, LinkedList(삭제시 자리이동 없음)

              add(Object o), remove(), element() 읽기 ; 예외발생 

 

Queue q = new LinkedList();

LinkedList ll = new LinkedList();

 

import java.util.*;

public class StackAndQueueEx {

  static final int MAX_SIZE = 5;
  static Queue<String> q = new LinkedList<>();

  public static void main(String[] args) {
    Collection<Integer> list = new HashSet<>();
    list.add(1);  list.add(2);  list.add(3);  list.add(4);  list.add(5);

    for (Integer integer : list)
      System.out.println(integer);

    Map<String, Integer> map = new HashMap<>();
    map.put("1", 10);
    map.put("2", 20);
    map.put("4", 40);
    map.put("5", 50);

    System.out.println(map.keySet()+" : "+map.values());
    System.out.println(map.entrySet());

    Stack<String> st = new Stack<>();

    String expression = "(2+3)*2 + (3/3)";

    try {
      for (int i = 0; i < expression.length(); i++) {
        char ch = expression.charAt(i);
        if ( ch== '(') st.push(ch+"");
        else if (ch== ')')    st.pop();
      }
      if (st.empty())  System.out.println("정상 수식");
       else  System.out.println("비 정상 수식");
    } catch (Exception e){
      System.out.println("비 정상 수식, by exception");
    }

    System.out.println("help는 도움말");

    while (true) {
      System.out.println(">>>>");
      try{
        Scanner sc = new Scanner(System.in);
        String input = sc.nextLine().trim();

        if("".equals(input)) continue;

        if(input.equalsIgnoreCase("q")){
          System.exit(0);
        } else if (input.equalsIgnoreCase("help")) {
          System.out.println("help 도움말");
          System.out.println("q/Q 종료");
          System.out.println("history 최근 입력" + MAX_SIZE+"개");
        } else if (input.equalsIgnoreCase("history")) {
          save(input);

          LinkedList<String> lList = (LinkedList<String>) q;

          int i=1;
          for (String str : lList)
            System.out.println((i++)+" : "+ str);
        } else {
          save(input);
          System.out.println(input);
        }
      } catch (Exception ignored){}
    }
  }

  private static void save(String input) {
    if (!"".equals(input)) q.offer(input);
    if (q.size() > MAX_SIZE) q.poll();
  }
}