文章目录

• 一.利用lambda对list集合排序
• • 1.升序排序
  • 2.降序排序
  • 对对象集合操作，其实与基本类型集合操作类似
  • 对 JSONArray 排序
• 二.java8-Lambda中比较器Comparator的使用
• • 不使用Lambda的排序
  • 通过Lambda进行排序
  • 更多的Lambda例子

一.利用lambda对list集合排序

先定义一个集合

List<Integer> list = new ArrayList<>();list.add(1);list.add(5);list.add(4);list.add(3);list.add(7);

1.升序排序

list.sort((a,b)->a.compareTo(b));

或

list.sort(Comparator.comparing(a->a));

或

list.sort((a,b)->a-b);

或

// 2、匿名内部类list.sort(new Comparator<Integer>() {@Overridepublic int compare(Integer o1, Integer o2) {return o1-o2;}});

2.降序排序

list.sort((a,b)->b-a);

匿名内部类方法

 list.sort(new Comparator<Integer>() {      @Override       public int compare(Integer o1, Integer o2) {              return o2-o1;       } });

对对象集合操作，其实与基本类型集合操作类似

List<User> list1 = new ArrayList<User>();User user = new User("张三", "15", "男");User user1 = new User("李四", "10", "男");list1.add(user);list1.add(user1);//1、年龄升序list1.sort((a,b) -> a.getAge().compareTo(b.getAge()));//2、姓名降序排列list1.sort(Comparator.comparing(User::getName).reversed());//等价于 2list1.sort(Comparator.comparing(a->((User)a).getAge()).reversed());//3、先按性别排，如果年龄相同，再按年龄排序list1.sort(Comparator.comparing(User::getSex).reversed().thenComparing(User::getAge));

对 JSONArray 排序

定义一个json数组 resultArray

JSONArray resultArray = new JSONArray();JSONObject result = new JSONObject();result.put("name","张三");result.put("age","15");result.put("data","201812130451");resultArray.add(result);//根据姓名的倒序排序resultArray.sort(Comparator.comparing(obj -> ((JSONObject) obj).getString("name")).reversed());//根据时间倒序排序resultArray.sort(Comparator.comparing(obj -> ((JSONObject) obj).getData("data")).reversed());//根据年龄升序排序resultArray.sort(Comparator.comparing(obj -> ((JSONObject) obj).getInteger("age")));

注意：reversed()函数的意思是将数组颠倒。其用法常见于字符串处理中，将字符串颠倒
如：

String str = "abcd";StringBuffer sb = new StringBuffer(str);sb.reverse();System.out.println(str);System.out.println(sb.toString());---------------------------------------输出abcddcba

二.java8-Lambda中比较器Comparator的使用

典型的比较器示例

Comparator<Developer> byName = new Comparator<Developer>() {    @Override    public int compare(Developer o1, Developer o2) {        return o1.getName().compareTo(o2.getName());    }};

等价的Lambda的方式

Comparator<Developer> byName = (Developer o1, Developer o2)->o1.getName().compareTo(o2.getName());

不使用Lambda的排序

假如我们要通过Developer 对象的年龄进行排序，通常情况下我们使用Collections.sort，new个匿名Comparator 类，类似下面这种：

import java.math.BigDecimal;import java.util.ArrayList;import java.util.Collections;import java.util.Comparator;import java.util.List;public class TestSorting {    public static void main(String[] args) {        List<Developer> listDevs = getDevelopers();        System.out.println("Before Sort");        for (Developer developer : listDevs) {            System.out.println(developer);        }        //sort by age        Collections.sort(listDevs, new Comparator<Developer>() {            @Override            public int compare(Developer o1, Developer o2) {                return o1.getAge() - o2.getAge();            }        });        System.out.println("After Sort");        for (Developer developer : listDevs) {            System.out.println(developer);        }    }    private static List<Developer> getDevelopers() {        List<Developer> result = new ArrayList<Developer>();        result.add(new Developer("ricky", new BigDecimal("70000"), 33));        result.add(new Developer("alvin", new BigDecimal("80000"), 20));        result.add(new Developer("jason", new BigDecimal("100000"), 10));        result.add(new Developer("iris", new BigDecimal("170000"), 55));        return result;    }}-----------------------------------------------------------------------------------------------------输出结果：Before SortDeveloper [name=ricky, salary=70000, age=33]Developer [name=alvin, salary=80000, age=20]Developer [name=jason, salary=100000, age=10]Developer [name=iris, salary=170000, age=55]After SortDeveloper [name=jason, salary=100000, age=10]Developer [name=alvin, salary=80000, age=20]Developer [name=ricky, salary=70000, age=33]Developer [name=iris, salary=170000, age=55]

当比较规则发生变化时，你需要再次new个匿名Comparator 类：

    //sort by age    Collections.sort(listDevs, new Comparator<Developer>() {        @Override        public int compare(Developer o1, Developer o2) {            return o1.getAge() - o2.getAge();        }    });    //sort by name    Collections.sort(listDevs, new Comparator<Developer>() {        @Override        public int compare(Developer o1, Developer o2) {            return o1.getName().compareTo(o2.getName());        }    });    //sort by salary    Collections.sort(listDevs, new Comparator<Developer>() {        @Override        public int compare(Developer o1, Developer o2) {            return o1.getSalary().compareTo(o2.getSalary());        }    });

这样也可以，不过你会不会觉得这样有点怪，因为其实不同的只有一行代码而已，但是却需要重复写很多代码？

通过Lambda进行排序

在java8中，List接口直接提供了排序方法， 所以你不需要使用Collections.sort

    //List.sort() since Java 8    listDevs.sort(new Comparator<Developer>() {        @Override        public int compare(Developer o1, Developer o2) {            return o2.getAge() - o1.getAge();        }    });

Lambda 示例

import java.math.BigDecimal;import java.util.ArrayList;import java.util.List;public class TestSorting {    public static void main(String[] args) {        List<Developer> listDevs = getDevelopers();        System.out.println("Before Sort");        for (Developer developer : listDevs) {            System.out.println(developer);        }        System.out.println("After Sort");        //lambda here!        listDevs.sort((Developer o1, Developer o2)->o1.getAge()-o2.getAge());        //java 8 only, lambda also, to print the List        listDevs.forEach((developer)->System.out.println(developer));    }    private static List<Developer> getDevelopers() {        List<Developer> result = new ArrayList<Developer>();        result.add(new Developer("ricky", new BigDecimal("70000"), 33));        result.add(new Developer("alvin", new BigDecimal("80000"), 20));        result.add(new Developer("jason", new BigDecimal("100000"), 10));        result.add(new Developer("iris", new BigDecimal("170000"), 55));        return result;    }}------------------------------------------------------------------------输出结果:Before SortDeveloper [name=ricky, salary=70000, age=33]Developer [name=alvin, salary=80000, age=20]Developer [name=jason, salary=100000, age=10]Developer [name=iris, salary=170000, age=55]After SortDeveloper [name=jason, salary=100000, age=10]Developer [name=alvin, salary=80000, age=20]Developer [name=ricky, salary=70000, age=33]Developer [name=iris, salary=170000, age=55]

更多的Lambda例子

根据年龄

    //sort by age    Collections.sort(listDevs, new Comparator<Developer>() {        @Override        public int compare(Developer o1, Developer o2) {            return o1.getAge() - o2.getAge();        }    });    //lambda    listDevs.sort((Developer o1, Developer o2)->o1.getAge()-o2.getAge());    //lambda, valid, parameter type is optional    listDevs.sort((o1, o2)->o1.getAge()-o2.getAge());

根据名字

    //sort by name    Collections.sort(listDevs, new Comparator<Developer>() {        @Override        public int compare(Developer o1, Developer o2) {            return o1.getName().compareTo(o2.getName());        }    });    //lambda    listDevs.sort((Developer o1, Developer o2)->o1.getName().compareTo(o2.getName()));    //lambda    listDevs.sort((o1, o2)->o1.getName().compareTo(o2.getName()));

根据薪水

    //sort by salary    Collections.sort(listDevs, new Comparator<Developer>() {        @Override        public int compare(Developer o1, Developer o2) {            return o1.getSalary().compareTo(o2.getSalary());        }    });    //lambda    listDevs.sort((Developer o1, Developer o2)->o1.getSalary().compareTo(o2.getSalary()));    //lambda    listDevs.sort((o1, o2)->o1.getSalary().compareTo(o2.getSalary()))

倒序
正常排序

Comparator<Developer> salaryComparator = (o1, o2)->o1.getSalary().compareTo(o2.getSalary());listDevs.sort(salaryComparator);

倒序

Comparator<Developer> salaryComparator = (o1, o2)->o1.getSalary().compareTo(o2.getSalary());listDevs.sort(salaryComparator.reversed());

参考文章侵删:
java 使用Lambda对集合排序
java8-Lambda中比较器Comparator的使用

来源地址：https://blog.csdn.net/mfysss/article/details/131208592