Question

如何实现对ArrayList排序 sort

Answer 1

package com.collection;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Test {
public static void main(String[] args) {

Student zlj = new Student("丁晓宇", 21);
Student dxy = new Student("赵四", 22);
Student cjc = new Student("张三", 11);
Student lgc = new Student("刘武", 19);

List<Student> studentList = new ArrayList<Student>();
studentList.add(zlj);
studentList.add(dxy);
studentList.add(cjc);
studentList.add(lgc);

System.out.println("按年龄升序：");
Collections.sort(studentList, new SortByAge());
for (Student student : studentList) {
System.out.println(student.getName() + " / " + student.getAge());
}
System.out.println();
System.out.println("按姓名排序：");
Collections.sort(studentList, new SortByName());
for (Student student : studentList) {
System.out.println(student.getName() + " / " + student.getAge());
}
}
}

class SortByAge implements Comparator {
public int compare(Object o1, Object o2) {
Student s1 = (Student) o1;
Student s2 = (Student) o2;
return s1.getAge().compareTo(s2.getAge());
// if (s1.getAge() > s2.getAge())
// return 1;
// return -1;
}
}

class SortByName implements Comparator {
public int compare(Object o1, Object o2) {
Student s1 = (Student) o1;
Student s2 = (Student) o2;
return s1.getName().compareTo(s2.getName());
}
}

输出结果：
按年龄升序：
张三 / 11
刘武 / 19
丁晓宇 / 21
赵四 / 22

按姓名排序：
丁晓宇 / 21
刘武 / 19
张三 / 11
赵四 / 22

Answer 2

现在java8帮你封装了一把，可以不用Colltion的sort方法啦，很简单 list.stream.sorted(); 就可以直接排序啦，对于基本类型的数据 若是一个对象的集合，比如List list这类的集合