Java List的排序

1、List的排序方式

1）list中对象实现Comparable接口，重写compareTo接口，排序的字段进行比较。

//懒，就写一起了
public class MainTest {
    //测试方法
    public static void main(String[] args) throws Exception {
        List<Person> listA = new ArrayList<Person>();
        listA.add(new Person("name2", 2));
        listA.add(new Person("name1", 1));
        listA.add(new Person("name3", 3));
        //升序
        Collections.sort(listA);
        System.out.println("**********升序**********");
        for (Person p : listA) {
            System.out.println(p);
        }
        //降序
        Collections.reverse(listA);
        System.out.println("**********降序**********");
        for (Person p : listA) {
            System.out.println(p);
        }

    }

    static class Person implements Comparable<Person> {

        private String name;
        private Integer order;

        @Override
        public String toString() {
            return "Person{" +
                    "order=" + order +
                    ", name='" + name + '\'' +
                    '}';
        }

        public Person(String name, Integer order){
            this.name = name;
            this.order = order;
        }

        public Integer getOrder() {
            return order;
        }

        @Override
        public int compareTo(Person arg0) {
            //升序
            return this.getOrder().compareTo(arg0.getOrder());
        }
    }
}

2）重载Collections.sort方法

//懒，就写一起了
public class MainTest {

    //测试方法
    public static void main(String[] args) throws Exception {
        List<Person> listA = new ArrayList<Person>();
        listA.add(new Person("name2", 2));
        listA.add(new Person("name1", 1));
        listA.add(new Person("name3", 3));

        System.out.println("**********升序**********");
        //升序
        Collections.sort(listA, new MySort());
        for (Person person : listA) {
            System.out.println(person);
        }
        //降序
        System.out.println("**********降序**********");
        Comparator result = Collections.reverseOrder(new MySort());
        Collections.sort(listA,result);
        for (Person person : listA) {
            System.out.println(person);
        }

        List<Person> listB = new ArrayList<Person>();
        listB.add(new Person("name2", 2));
        listB.add(new Person("name1", 1));
        listB.add(new Person("name3", 3));
        //换一种写法
        Collections.sort(listB, new Comparator<Person>() {
            @Override
            public int compare(Person p1, Person p2) {
                return p1.getOrder().compareTo(p2.getOrder());
            }
        });
        System.out.println("**换一种写法 升序**********");
        for (Person person : listB) {
            System.out.println(person);
        }
    }
    //比较器类
    static class MySort implements Comparator{
        @Override
        public int compare(Object o1, Object o2){
            Person p1 = (Person)o1;
            Person p2 = (Person)o2;
            //升序
            return p1.getOrder() - p2.getOrder();
        }
    }
    //比较对象
    static class Person {

        private String name;
        private Integer order;

        @Override
        public String toString() {
            return "Person{" +
                    "order=" + order +
                    ", name='" + name + '\'' +
                    '}';
        }

        public Person(String name, Integer order){
            this.name = name;
            this.order = order;
        }

        public Integer getOrder() {
            return order;
        }
    }
}