2020-09-06-白红宇

2020-09-06

阅读量：2289 次

发布时间：2019-05-09

本文共 2182 字，大约阅读时间需要 7 分钟。

一、Iterator和ListIterator的区别

Iterator:

只能按次序从前往后遍历，只能读，

ListIterator

1）允许我们向前、向后两个方向遍历 List;

2）在遍历时可以修改List 的元素

3）制定元素开始遍历

二、CopyOnWriteArrayList

CopyOnWriteArrayList

写时复制：写操作的时候，把List复制一份做写操作，操作完复制回去

弱点：

弱一致性

浪费内存

三、HashMap和TreeMap

HashMap：

没有顺序，key散列算法

TreeMap：

保证顺序

四、comparable和comparator

comparable

comparator

public class User implements Comparable
   
     {    @Override    public int compareTo(User o) {        return this.age - o.age;    }    private int age ;    private String name ;    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}public class User2  {    private int age ;    private String name ;    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}public class UserComparator implements Comparator
    
      {    @Override    public int compare(User2 o1, User2 o2) {        return o1.getAge()-o2.getAge();    }}public class CompareTest {    public static void main(String[] args) {        try{            TreeSet
     
       treeSet1 = new TreeSet
      
       ();            User user1 = new User();            user1.setAge(10);            user1.setName("name_10");            User user2 = new User();            user2.setAge(20);            user2.setName("name_20");            User user3 = new User();            user3.setAge(9);            user3.setName("name_9");            treeSet1.add(user1);            treeSet1.add(user2);            treeSet1.add(user3);            TreeSet
       
         treeSet2 = new TreeSet
        
         (new UserComparator()); User2 user21 = new User2(); user21.setAge(10); user21.setName("name_10"); User2 user22 = new User2(); user22.setAge(20); user22.setName("name_20"); User2 user23 = new User2(); user23.setAge(9); user23.setName("name_9"); treeSet2.add(user21); treeSet2.add(user22); treeSet2.add(user23); String d = null; }catch (Exception e){ e.printStackTrace(); } }}