List,Set,Map用法以及区别

<span style="box-sizing: inherit; -webkit-tap-highlight-color: transparent; font-stretch: normal; font-size: 14px; line-height: 25px; font-family: Helvetica, Tahoma, Arial, sans-serif;">转载 https://my.oschina.net/u/933822/blog/391954</span>

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<span style="box-sizing: inherit; -webkit-tap-highlight-color: transparent; font-stretch: normal; font-size: 14px; line-height: 25px; font-family: Helvetica, Tahoma, Arial, sans-serif;">List特点：元素有放入顺序，元素可重复<span style="box-sizing: inherit; -webkit-tap-highlight-color: transparent;"> </span></span><br style="box-sizing: inherit; -webkit-tap-highlight-color: transparent; color: rgb(61, 70, 77); font-family: "Pingfang SC", STHeiti, "Lantinghei SC", "Open Sans", Arial, "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", SimSun, sans-serif; font-size: 16px; line-height: 28px; background-color: rgb(248, 248, 248);" /><span style="box-sizing: inherit; -webkit-tap-highlight-color: transparent; font-stretch: normal; font-size: 14px; line-height: 25px; font-family: Helvetica, Tahoma, Arial, sans-serif;">Map特点：元素按键值对存储，无放入顺序<span style="box-sizing: inherit; -webkit-tap-highlight-color: transparent;"> </span></span><br style="box-sizing: inherit; -webkit-tap-highlight-color: transparent; color: rgb(61, 70, 77); font-family: "Pingfang SC", STHeiti, "Lantinghei SC", "Open Sans", Arial, "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", SimSun, sans-serif; font-size: 16px; line-height: 28px; background-color: rgb(248, 248, 248);" /><span style="box-sizing: inherit; -webkit-tap-highlight-color: transparent; font-stretch: normal; font-size: 14px; line-height: 25px; font-family: Helvetica, Tahoma, Arial, sans-serif;">Set特点：元素无放入顺序，元素不可重复（注意：元素虽然无放入顺序，但是元素在set中的位置是有该元素的HashCode决定的，其位置其实是固定的）</span>

import java.util.*;public class Test{public static void main(String [] arge){List list = new ArrayList();list.add(0, "a");list.add(1, "b");list.add(2, "c");list.add(3, "d");while(Iterator it = list.iterator();it.hasNext()){   Object element = it.next();   System.out.println (element);}}}List、Map、SetList 通过下标来存取 和值来存取Map 键值对应来存取 set 存取元素是无序的--------------------------------------------------------------------package com.operation;import java.util.ArrayList;import java.util.HashSet;import java.util.Iterator;import java.util.List;import java.util.Set;import java.util.TreeSet;public class User {private Integer userId;private String userName;private String address;public User(int userId, String userName, String address) {   this.userId = userId;   this.userName = userName;   this.address = address;}public String getAddress() {   return address;}public void setAddress(String address) {   this.address = address;}public Integer getUserId() {   return userId;}public void setUserId(Integer userId) {   this.userId = userId;}public String getUserName() {   return userName;}public void setUserName(String userName) {   this.userName = userName;}public static void main(String[] args) {//   Map<Integer, User> map = new TreeMap<Integer, User>();//   map.put(1, new User(1,"李伟","beijing"));//   map.put(2, new User(2,"王文军","beijing"));//  //   map.put(4, new User(2,"abc","beijing"));//   map.put(5, new User(2,"abc","beijing"));//  //  //  //   Set<Integer> keys = map.keySet();//  ////   Iterator<Integer> it = keys.iterator();////   while (it.hasNext()) {////    Integer key = it.next();////    User user = map.get(key);////    System.out.println("key = " + key + "\t" + "value = " + user.getUserName());////   }//  //   for (Integer key : keys) {//    User user1 = map.get(key);//    System.out.println("key = " + key + "\t" + "value = " + user1.getUserName());//   }      Set<String> set = new HashSet<String>();   set.add("a");   set.add("b");   set.add("c");   set.add("d");   set.add("d");   set.add("d");   set.add("d");   set.add("uuu");   set.add("e");       Iterator<String> it = set.iterator();   while (it.hasNext()) {    System.out.println(it.next());   }  }}

import java.util.*;public class Test{public static void main(String [] arge){List list = new ArrayList();list.add(0, "a");list.add(1, "b");list.add(2, "c");list.add(3, "d");while(Iterator it = list.iterator();it.hasNext()){   Object element = it.next();   System.out.println (element);}}}List、Map、SetList 通过下标来存取 和值来存取Map 键值对应来存取 set 存取元素是无序的--------------------------------------------------------------------package com.operation;import java.util.ArrayList;import java.util.HashSet;import java.util.Iterator;import java.util.List;import java.util.Set;import java.util.TreeSet;public class User {private Integer userId;private String userName;private String address;public User(int userId, String userName, String address) {   this.userId = userId;   this.userName = userName;   this.address = address;}public String getAddress() {   return address;}public void setAddress(String address) {   this.address = address;}public Integer getUserId() {   return userId;}public void setUserId(Integer userId) {   this.userId = userId;}public String getUserName() {   return userName;}public void setUserName(String userName) {   this.userName = userName;}public static void main(String[] args) {//   Map<Integer, User> map = new TreeMap<Integer, User>();//   map.put(1, new User(1,"李伟","beijing"));//   map.put(2, new User(2,"王文军","beijing"));//  //   map.put(4, new User(2,"abc","beijing"));//   map.put(5, new User(2,"abc","beijing"));//  //  //  //   Set<Integer> keys = map.keySet();//  ////   Iterator<Integer> it = keys.iterator();////   while (it.hasNext()) {////    Integer key = it.next();////    User user = map.get(key);////    System.out.println("key = " + key + "\t" + "value = " + user.getUserName());////   }//  //   for (Integer key : keys) {//    User user1 = map.get(key);//    System.out.println("key = " + key + "\t" + "value = " + user1.getUserName());//   }      Set<String> set = new HashSet<String>();   set.add("a");   set.add("b");   set.add("c");   set.add("d");   set.add("d");   set.add("d");   set.add("d");   set.add("uuu");   set.add("e");       Iterator<String> it = set.iterator();   while (it.hasNext()) {    System.out.println(it.next());   }  }}