List,Set,Map用法以及区别_存一批id用map还是set-优快云博客

本文深入探讨了Java集合框架中的三种主要类型：List、Map和Set。详细解释了每种类型的特性，例如List按顺序存储可重复元素，Map通过键值对进行存储，而Set则存储不重复且无序的元素。并通过示例代码展示了如何使用这些集合。

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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;">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、Set
List 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()); } }}