简介
本文用示例介绍Java的List（ArrayList、LinkedList等）的去重的方法。
List去重的方法
一共有这几种方法（按推荐顺序排列）：
JDK8的stream的distinct
转为HashSet（分不保持顺序和保持顺序两种） 转为TreeSet 使用retainAll/removeAll、contains、equals等基本方法
直接去重
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package com.example.a;
import java.util.*; import java.util.stream.Collectors;
public class Demo { public static void main(String[] args) { List<Integer> list = new ArrayList<>(); list.add( 1 ); list.add( 3 ); list.add( 2 ); list.add( 3 );
System.out.println( "源数据： " + list); System.out.println( "stream： " + stream(list)); System.out.println( "hashSetWithoutOrder：" + hashSetWithOrder(list)); System.out.println( "hashSetWithOrder： " + hashSetWithOrder(list)); System.out.println( "treeSet： " + treeSet(list)); }
//JDK1.8的stream去重 private static List<Integer> stream(List<Integer> list) { return list.stream().distinct().collect(Collectors.toList()); }
//HashSet（不保持顺序） private static List<Integer> hashSetWithoutOrder(List<Integer> list) { HashSet<Integer> h = new HashSet<Integer>(list); return new ArrayList<>(h); }
// 删除ArrayList中重复元素，保持顺序 public static List<Integer> hashSetWithOrder(List<Integer> list) { Set<Integer> set = new HashSet<Integer>(); List<Integer> newList = new ArrayList<Integer>(); for (Integer element : list) { if (set.add(element)) newList.add(element); } return newList; }
//TreeSet（自动排序） public static List<Integer> treeSet(List<Integer> list) { TreeSet<Integer> set = new TreeSet<Integer>(list); return new ArrayList<>(set); } } |
执行结果
源数据： [1, 3, 2, 3]
stream： [1, 3, 2]
hashSetWithoutOrder：[1, 3, 2]
hashSetWithOrder： [1, 3, 2]
treeSet： [1, 2, 3]
根据对象属性去重
法1：TreeSet
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Set<User> setByName = new TreeSet<User>((o1, o2) -> o1.getName()测试数据pareTo(o2.getName())); setByName.addAll(list); List<User> listByName = new ArrayList<>(setByName); System.out.println(listByName); //[User{name='Pepper', age=20, Phone='123'}, User{name='Tony', age=20, Phone='12'}]
Set<User> setByNameAndAge = new TreeSet<User>((o1, o2) -> { return (o1.getName() + o1.getAge())测试数据pareTo((o2.getName() + o2.getAge())); // return o1.getName()测试数据pareTo(o2.getName()) == 0 // ? o1.getAge()测试数据pareTo(o2.getAge()) // : o1.getName()测试数据pareTo(o2.getName()); }); setByNameAndAge.addAll(list); List<User> listByNameAndAge = new ArrayList<>(setByNameAndAge); System.out.println(listByNameAndAge); //[User{name='Pepper', age=20, Phone='123'}, // User{name='Tony', age=20, Phone='12'}, // User{name='Tony', age=22, Phone='1234'}] |
法2：stream+TreeSet
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List<User> streamByNameList = list.stream().collect(Collectors.collectingAndThen( Collectors.toCollection(() -> new TreeSet<>(Comparator测试数据paring(User::getName))), ArrayList:: new )); System.out.println(streamByNameList); //[User{name='Pepper', age=20, Phone='123'}, User{name='Tony', age=20, Phone='12'}]
List<User> streamByNameAndAgeList = list.stream().collect(Collectors.collectingAndThen( Collectors.toCollection( () -> new TreeSet<>(Comparator测试数据paring(o -> o.getName() + o.getAge()))), ArrayList:: new )); System.out.println(streamByNameAndAgeList); //[User{name='Pepper', age=20, Phone='123'}, // User{name='Tony', age=20, Phone='12'}, // User{name='Tony', age=22, Phone='1234'}] |
所有代码
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package org.example.a;
import java.util.*; import java.util.stream.Collectors;
class User { private String name; private Integer age; private String Phone;
public User(String name, Integer age, String phone) { this .name = name; this .age = age; Phone = phone; }
public String getName() { return name; }
public void setName(String name) { this .name = name; }
public Integer getAge() { return age; }
public void setAge(Integer age) { this .age = age; }
public String getPhone() { return Phone; }
public void setPhone(String phone) { Phone = phone; }
@Override public String toString() { return "User{" + "name='" + name + '\ '' + ", age=" + age + ", Phone='" + Phone + '\ '' + '}' ; } }
public class Demo { public static void main(String[] args) { List<User> list = new ArrayList<User>() {{ add( new User( "Tony" , 20 , "12" )); add( new User( "Pepper" , 20 , "123" )); add( new User( "Tony" , 22 , "1234" )); }};
Set<User> setByName = new TreeSet<User>((o1, o2) -> o1.getName()测试数据pareTo(o2.getName())); setByName.addAll(list); List<User> listByName = new ArrayList<>(setByName); System.out.println(listByName); //[User{name='Pepper', age=20, Phone='123'}, User{name='Tony', age=20, Phone='12'}]
Set<User> setByNameAndAge = new TreeSet<User>((o1, o2) -> { return (o1.getName() + o1.getAge())测试数据pareTo((o2.getName() + o2.getAge())); // return o1.getName()测试数据pareTo(o2.getName()) == 0 // ? o1.getAge()测试数据pareTo(o2.getAge()) // : o1.getName()测试数据pareTo(o2.getName()); }); setByNameAndAge.addAll(list); List<User> listByNameAndAge = new ArrayList<>(setByNameAndAge); System.out.println(listByNameAndAge); //[User{name='Pepper', age=20, Phone='123'}, // User{name='Tony', age=20, Phone='12'}, // User{name='Tony', age=22, Phone='1234'}]
List<User> streamByNameList = list.stream().collect(Collectors.collectingAndThen( Collectors.toCollection( () -> new TreeSet<>(Comparator测试数据paring(User::getName))), ArrayList:: new )); System.out.println(streamByNameList); //[User{name='Pepper', age=20, Phone='123'}, User{name='Tony', age=20, Phone='12'}]
List<User> streamByNameAndAgeList = list.stream().collect(Collectors.collectingAndThen( Collectors.toCollection( () -> new TreeSet<>(Comparator测试数据paring(o -> o.getName() + o.getAge()))), ArrayList:: new )); System.out.println(streamByNameAndAgeList); //[User{name='Pepper', age=20, Phone='123'}, // User{name='Tony', age=20, Phone='12'}, // User{name='Tony', age=22, Phone='1234'}] } } |
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原文链接：https://blog.csdn.net/feiying0canglang/article/details/124853472
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