【学习笔记】【JAVA】【Collections】【Comparator】返回数据中，根据一个数据索引排序。（完整代码）

【例子】：根据图中rise数据（学校人数）索引进行排序。（①升序：由小到大 ②降序：由大到小）

【解】：（注：rise是整数型，1是升序，由小到大；0是降序，由大到小）

【代码】：
【StundentBean】

public class StudentBean {
    
    
	// 学生名字
	private String sname;

	public String getSname() {
    
    
		return sname;
	}

	public void setSname(String sname) {
    
    
		this.sname = sname;
	}
}

【SchoolVO】

import java.util.List;

public class SchoolVO {
    
    
	// 学校名字
	private String name;
	// 学校历史
	private String history;
	// 学校年龄
	private Integer age;
	// 学生总数
	private Integer sum;
	
	// 学校具体信息（班级、学生等信息），？：泛型（可以是实体类，Map等）
	private List<?> list;
	
	public String getName() {
    
    
		return name;
	}
	public void setName(String name) {
    
    
		this.name = name;
	}
	public String getHistory() {
    
    
		return history;
	}
	public void setHistory(String history) {
    
    
		this.history = history;
	}
	public Integer getAge() {
    
    
		return age;
	}
	public void setAge(Integer age) {
    
    
		this.age = age;
	}
	public List<?> getList() {
    
    
		return list;
	}
	public void setList(List<?> list) {
    
    
		this.list = list;
	}
	public Integer getSum() {
    
    
		return sum;
	}
	public void setSum(Integer sum) {
    
    
		this.sum = sum;
	}
	
}

【测试类】

	@GetMapping("/test")
	public Map<String, Object> test(Integer rise) {
    
    
		Map<String, Object> map = new HashMap<String, Object>();
		List<SchoolVO> list = new ArrayList<>();

		// 第一中学的情况
		List<StudentBean> students_1 = new ArrayList<>();
		StudentBean xiaoming = new StudentBean();
		StudentBean xiaojun = new StudentBean();
		StudentBean xiaohong = new StudentBean();
		xiaoming.setSname("小明");
		xiaojun.setSname("小军");
		xiaohong.setSname("小红");
		students_1.add(xiaoming);
		students_1.add(xiaojun);
		students_1.add(xiaohong);
		SchoolVO school_1 = new SchoolVO();
		school_1.setName("第一中学");
		school_1.setAge(4);
		school_1.setHistory("第一中学，历史悠久，诞生于2017年");
		school_1.setSum(students_1.size());
		school_1.setList(students_1);

		// 第二中学的情况
		List<StudentBean> students_2 = new ArrayList<>();
		StudentBean xiaohei1 = new StudentBean();
		StudentBean xiaobai1 = new StudentBean();
		StudentBean xiaohei2 = new StudentBean();
		StudentBean xiaobai2 = new StudentBean();
		xiaohei1.setSname("小黑1");
		xiaobai1.setSname("小白1");
		xiaohei2.setSname("小黑2");
		xiaobai2.setSname("小白2");
		students_2.add(xiaohei1);
		students_2.add(xiaobai1);
		students_2.add(xiaohei2);
		students_2.add(xiaobai2);
		SchoolVO school_2 = new SchoolVO();
		school_2.setName("第二中学");
		school_2.setAge(3);
		school_2.setHistory("第二中学，历史悠久，诞生于2018年");
		school_2.setSum(students_2.size());
		school_2.setList(students_2);

		// 第三中学的情况
		List<StudentBean> students_3 = new ArrayList<>();
		StudentBean xiaoxiao = new StudentBean();
		StudentBean xiaotian = new StudentBean();
		xiaoxiao.setSname("小小");
		xiaotian.setSname("小天");
		students_3.add(xiaoxiao);
		students_3.add(xiaotian);
		SchoolVO school_3 = new SchoolVO();
		school_3.setName("第三中学");
		school_3.setAge(3);
		school_3.setHistory("第三中学，历史悠久，诞生于2018年");
		school_3.setSum(students_3.size());
		school_3.setList(students_3);

		// 把三个中学放一起
		list.add(school_1);
		list.add(school_2);
		list.add(school_3);

		// ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓排序功能（核心代码）↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓
		if (rise != null && rise == 1) {
    
    
			Collections.sort(list, new Comparator<SchoolVO>() {
    
    
				@Override
				public int compare(SchoolVO o1, SchoolVO o2) {
    
    
					return o1.getSum() - o2.getSum();
				}
			});
		} else if (rise != null && rise == 0) {
    
    
			Collections.sort(list, new Comparator<SchoolVO>() {
    
    
				@Override
				public int compare(SchoolVO o1, SchoolVO o2) {
    
    
					return o2.getSum() - o1.getSum();
				}
			});
		}
		// ↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑排序功能（核心代码）↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑
		
		map.put("data", list);
		map.put("flag", 1);
		map.put("msg", "查询成功");
		return map;
	}

【升序】：rise = 1

【降序】：rise = 0