자바 List,Set,Map 기능설명(1)

--List의 관한 설명(1)--

 

import java.util.List;
import java.util.Vector;
import java.beans.VetoableChangeListenerProxy;
import java.util.ArrayList;
import java.util.LinkedList;


public class ListTest {

public static void main(String[] args) {

//Collection 클래스들 : 자료구조를 구현한 java API 클래스들-대량의 데이터를 관리

//배열과 차이점
//배열은 데이터를 삽입,삭제하는 것이 매우 번거로움. 그리고 개수가 미리 정해져야함. 이건 불편

//데이터의 동적추가/삭제/삽입등을 편하게 코팅할 수 있는 기능을 가진 클래스들 Collection

//컬렉션은 저장방식에 따라 크게 3가지 방식으로 분류함

//1. List : 자료들이 저장된 순서대로 있음 자동으로 부여된 인덱스번호로 요소를 구분함 중복된 데이터의 저장도 가능함 예시)기차 중간에 자료를 넣어도 연결 끊고 중간
                                                                                               //삽입하면 뒤에 자료들 번호가 자동으로 밀림 
//2. Set : 저장된 순서 x,인덱스 번호 x , 중복된 데이터 허용 x 예시)햄버거 셋트-햄버거,콜라,감자튀김이 셋트면 햄버거 햄버거 햄버거 셋트는 안됨 중복된 데이터 ㄴㄴ
                                                       //순서는 상관 없음 콜라,감자튀김,햄버거 그냥 셋트메뉴인것만 들어있다면 상관없음  
//3. Map : 저장된 순서 x,인덱스 번호 대신에 식별자를 사용,중복된 식별자는 허용x, 중복된 데이터는 허용 o  //식별자를 번호 대신에 이름으로 사용가능 
                                                                                      //내가 원하는걸 이름을 정해서 꺼내쓸수 있다

//가장 많이 사용될 List계열 부터 실습
//List는 인터페이스임 즉 직접 객체 생성이 불가능
//List list=new List();

//List 인터페이스의 추상메소드들을 구현한 하위 클래스들이 존재함
//List계열 : ArrayList ,LinkedList, Vector

//이중 가장 많이 사용되는 ArrayList 클래스를 사용해보기

ArrayList<String> list=new ArrayList<String>();

//ArrayList 객체가 보유한 유용한 기능메소드들...

//1.요소의 개수
System.out.println("요소 개수 : "+list.size());
//2.요소의 추가
String s= new String("aa");
list.add(s);
list.add(new String("bb")); //자동으로 배열처럼 0번 부터 순서 정해짐
list.add("cc"); //자동 new String()
System.out.println("요소 개수 : "+list.size());

//3.요소 얻어오기
String ss=list.get(0);
System.out.println(ss);
System.out.println(list.get(1));
System.out.println(list.get(2));

//System.out.println(list.get(3)); error 개수보다 많은걸 할경우

//4.요소 삭제하기
list.remove(1);
System.out.println("요소 개수 : "+list.size());
System.out.println(list.get(0));
System.out.println(list.get(1));

//5.특정 위치에 요소를 삽입하기
list.add(1,"dd");
System.out.println(list.get(0));
System.out.println(list.get(1));
System.out.println(list.get(2));

//6.요소를 삭제할때 인덱스번호가 아니라 참조변수의 주소값으로 제거 가능
String s2=new String("Test");
list.add(s2);
System.out.println("요소 개수 : "+list.size());
list.remove(s2);   //인덱스 숫자로만 지우면 헷갈릴수도 있으니 지정했던 객체의 주소로 지울수도 있다(참조변수로 지우는것)

//7.요소 모두 지우기
list.clear();
System.out.println("요소 개수 : "+list.size());

//8.리스트계열은 중복된 데이터의 저장을 허용함
list.add("aa");
list.add("aa");
list.add("aa");
System.out.println("요소 개수 : "+list.size());

//9.리스트안에 요소가 비어있는지 여부(ture/false)를 알려주는 기능메소드
//list.clear();
System.out.println(list.size()==0);  //내가 계산한것
System.out.println(list.isEmpty());  //같은 질문이지만 계산 않한것

//10.특정 데이터가 리스트안에 있는지 여부(boolean)
System.out.println(list.contains("aa"));
System.out.println(list.contains("bb"));

//11.한번에 여러요소들을(다른 리스트 객체의 요소들) 추가하기
list.clear();
list.add("aa");
list.add("bb");
list.add("cc");

//또 다른 리스트객체
ArrayList<String>list2=new ArrayList<String>();

list2.add("kk");
list2.add("ss");

list.addAll(list2);
System.out.println(list.toString());  //.toString()이 오버라이드 되어 있음. 요소값들이[,,,,],를 구분자로 하여 문자열로 리턴됨

//11.1 특정위치에 여러개를 한번에 추가하기
list.addAll(1, list2);
System.out.println(list.toString());

//12. 특정 요소들은 한번에 제거하기
ArrayList<String>list3=new ArrayList<String>();

//제거할 요소목록을 추가
list3.add("aa");
list3.add("kk");

list.removeAll(list3);
System.out.println(list); //자동.toString()

//13. 특정요소들만 남기도 나머지 모두 제거하기

ArrayList<String>list4=new ArrayList<String>();
list4.add("bb");
list4.add("cc");

list.retainAll(list4);
System.out.println(list);

//14. 특정요소가 몇번째 index에 있는지를 알려주는 기능
System.out.println(list.indexOf("cc"));
System.out.println(list.indexOf("ee")); //못찾으면 -1

//요소들을 순차적으로 접근하여 얻어오기..
list.clear();
list.add("aa");
list.add("bb");
list.add("cc");
list.add("dd");
list.add("ee");
list.add("aa");  //중복도 가능

//방법 1. for문 사용하기
for(int i=0; i<list.size(); i++) {
String t=list.get(i);
System.out.println(list.get(i));
}
System.out.println();

//방법2. 확장된 for문법 [for each문]
for( String t : list) {    //단점은 중간 숫자부터 여기까지 역차순 이런기능이 안된다.
System.out.println(t); //간단해서 좋지만 할수있는거는 각각에 대하여 정해진대로 순차적인 것만 가능
}

//방법3. iterator(반복자)를 이용하는 방법 ..set에서 소개예정

//---------------------------------------------------------------------

//List계열의 하위 클래스 중 LinkedList...
//문법적 사용모습의 거의 똑같음 다만 성능의차이..
//ArrayList에 비해 요소의 삽입,삭제등이 빠름,대신 특정 요소에 접근은 느림

LinkedList<String> aaa=new LinkedList<String>();
System.out.println("요소개수 : "+aaa.size());

aaa.add("aaa");
aaa.add("bbb");
aaa.add("ccc");

System.out.println(aaa.get(0));
System.out.println(aaa.get(1));
System.out.println(aaa.get(2));

aaa.remove(1);
System.out.println("요소개수 : "+aaa.size());

//요즘은 컴퓨터 성능이 좋아져서 차이가 거의 없음. 일반적으로는 ArrayList를 선호함.

//마지막 Vactor- 사용법 같은 ArrayList와 완전동작이 같음 [단 동기화처리가 되어 있다는 차이만 있음]

Vector<String> bbb=new Vector<String>();
bbb.add("aaa");
System.out.println(bbb.get(0));
System.out.println(bbb.size());