Java数组排序

直接Arrays.sort()方法，默认升序。 

Arrays.sort(a);

要实现降序排列需要实现Comparator<Integer>接口，重写里面的compare()方法；

代码如下

public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		Integer[]a= {1,9,878,3,55,268,999};
		Comparator<Integer> c=new cmp();
		Arrays.sort(a, c);;
		for(int i:a) {
			System.out.println(i);
		}
	}
class cmp implements Comparator<Integer> {
	public int compare(Integer a,Integer b) {
		return a-b;
	}
}

在重写compare() 的时候必须要用一个具体的类实现，而基本数据类型对应的类就是它的包装类，所以此处用的Integer；

compare 默认从小到大，即a-b>0的时候是升序，降序return b-a;

 

具体例子如下面一段代码：

对student对象分别对id，age升序排列：

public class Student  {
    private int id;
    private int age;
    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", age=" + age +
                '}';
    }
    public Student(int id, int age){
        this.id = id;
        this.age = age;
    }
//通过id排序
    public static class SortById implements Comparator<Student>{
        @Override
        public int compare(Student o1, Student o2) {
            return o1.id - o2.id;
        }
    }
//通过age排序
    public static class SortByAge implements Comparator<Student>{
        @Override
        public int compare(Student o1, Student o2) {
            return o1.age - o2.age;
        }
    }
    public static void main(String[] args) {
        Student s1 = new Student(11110,13);
        Student s2 = new Student(11112,12);
        Student[] ss = {s1, s2};
        Arrays.sort(ss,new SortById());
        for (Student s : ss) {
            System.out.print(s);
        }
        System.out.println();
        Arrays.sort(ss,new SortByAge());
        for (Student s : ss) {
            System.out.print(s);
        }
    }
}