Java针对ArrayList自定义排序的2种实现方法

1. 让需要进行排序的对象的类实现Comparable接口，重写compareTo(To)方法，在其中定义排序规则，那么就可以直接调用Collections.sort()来排序对象数组

public class Student implements Comparable{
    private int id;
    private int age;
    private int height;
    private String name;
    public Student(int id, String name, int age, int height) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.height = height;
    }
    public int getId() {
        return id;
    }
    public int getAge() {
        return age;
    }
    public int getHeight() {
        return height;
    }
    public String getName() {
        return name;
    }
    public void setId(int id) {
        this.id = id;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void setHeight(int height) {
        this.height = height;
    }
    @Override
    public int compareTo(Object o) {
        Student s = (Student) o;
        if (this.age > s.age) {
            return 1;
        }else if (this.age < s.age) {
            return -1;
        }else {
            if (this.height >= s.height) {
                return 1;
            }else {
                return -1;
            }
        }
    }
}

测试类：

public class Test {
    public static void printData(List<Student> list) {
        for (Student student : list) {
            System.out.println("学号:"+student.getId()+"姓名:"+student.getName()+
"年龄"+student.getAge()+"身高:"+student.getHeight());
        }
    }
    public static void main(String[] args) {
        List<Student> list = new ArrayList<>();
        list.add(new Student(1, "A", 20, 180));
        list.add(new Student(2, "B", 21, 175));
        list.add(new Student(3, "C", 22, 190));
        list.add(new Student(4, "D", 21, 170));
        list.add(new Student(5, "E", 20, 185));
        System.out.println("before sorted");
        printData(list);
        Collections.sort(list);
        System.out.println("after age and height sorted");
        printData(list);
    }
}

结果：

before sorted
学号:1姓名:A年龄20身高:180
学号:2姓名:B年龄21身高:175
学号:3姓名:C年龄22身高:190
学号:4姓名:D年龄21身高:170
学号:5姓名:E年龄20身高:185
after age and height sorted
学号:1姓名:A年龄20身高:180
学号:5姓名:E年龄20身高:185
学号:4姓名:D年龄21身高:170
学号:2姓名:B年龄21身高:175
学号:3姓名:C年龄22身高:190

2. 实现比较器接口Comparator，重写compare方法，直接当做参数传进sort中

public class Student {
    private int id;
    private int age;
    private int height;
    private String name;
    public Student(int id, String name, int age, int height) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.height = height;
    }
    public int getId() {
        return id;
    }
    public int getAge() {
        return age;
    }
    public int getHeight() {
        return height;
    }
    public String getName() {
        return name;
    }
    public void setId(int id) {
        this.id = id;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void setHeight(int height) {
        this.height = height;
    }
}

测试类：

public class Test {

    public static void main(String[] args) {
        List<Student> list = new ArrayList<>();
        list.add(new Student(1, "A", 20, 180));
        list.add(new Student(2, "B", 21, 175));
        list.add(new Student(3, "C", 22, 190));
        list.add(new Student(4, "D", 21, 170));
        list.add(new Student(5, "E", 20, 185));
        System.out.println("before sorted");
        printData(list);
        Collections.sort(list, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                if(o1.getAge() >= o2.getAge()) {
                    return 1;
                }
                else {
                    return -1;
                }
            }
        });
        System.out.println("after age sorted");
        printData(list);
        Collections.sort(list, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                if(o1.getAge() > o2.getAge()) {
                    return 1;
                }else if (o1.getAge() < o2.getAge()){
                    return -1;
                }else {
                    if (o1.getHeight() >= o2.getHeight()) {
                        return 1;
                    }else {
                        return -1;
                    }
                }
            }
        });
        System.out.println("after age and height sorted");
        printData(list);
    }
    public static void printData(List<Student> list) {
        for (Student student : list) {
            System.out.println("学号:"+student.getId()+"姓名:"+student.getName()+
"年龄"+student.getAge()+"身高:"+student.getHeight());
        }
    }
}

输出结果：

before sorted
学号:1姓名:A年龄20身高:180
学号:2姓名:B年龄21身高:175
学号:3姓名:C年龄22身高:190
学号:4姓名:D年龄21身高:170
学号:5姓名:E年龄20身高:185
after age sorted
学号:1姓名:A年龄20身高:180
学号:5姓名:E年龄20身高:185
学号:2姓名:B年龄21身高:175
学号:4姓名:D年龄21身高:170
学号:3姓名:C年龄22身高:190
after age and height sorted
学号:1姓名:A年龄20身高:180
学号:5姓名:E年龄20身高:185
学号:4姓名:D年龄21身高:170
学号:2姓名:B年龄21身高:175
学号:3姓名:C年龄22身高:190

单从上面的例子可以看出排序是稳定的，查看java的Collections.sort的源代码，确实是基于稳定的归并排序实现的，内部还做了优化，叫TimSort）。

哈二奇