Comparator多级排序

2022-07-18 12:48:23

       JDK里的Comparator方法为用户提供了自定义排序规则的接口,而我们在实际使用是一般也只是用了一个排序维度,本文介绍下多级或多个维度的排序需求下的接口实现。

       我们假设一个雇员对象,包含级别、工资和入职年份(为了简单,这些属性写成 public),代码如下:

public Class Employee {
 
    public int level;  //级别
    public int salary; //工资
    public int years;  //入职年数
 
}

       现在我需要做一个这样的雇员列表,首先级别最高的排在前面,如果级别相等,那么按工资排序,工资高的排在前面,如果工资相当则按入职年数排序,入职时间最长的排在前面。

       因为雇员列表是在内存中的一个 List<Employee> 对象,现在要对这个 List 中的雇员按上面的要求进行排序 Collections.sort(employeeList, comparator),那么这个 Comparator 应该怎么写呢?

下面这种肯定是不对的

Comparator<Employee> cp_by_default = new Comparator<Employee>(){
    @Override
    public int compare(Employee a1, Employee a2) {
        int a = a2.level - a1.level;
        if(a > 0)
            return a;
        a = a2.salary - a1.salary;
        if(a > 0)
            return a;
        return a2.years - a1.years;
    }       
};

 正确参考代码写法如下

package net.oschina.tester;
 
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
 
/**
 * 多个排序条件测试
 */
public class Employee {
 
    public static void main(String[] args) {
        List<Employee> objs = new ArrayList<Employee>(){{
            add(new Employee(5,3,5000,2));
            add(new Employee(1,9,10000,10));
            add(new Employee(4,5,8000,6));
            add(new Employee(2,9,12000,7));
            add(new Employee(6,1,2000,1));
            add(new Employee(3,5,8000,12));
        }};
        Collections.sort(objs, comparator);
        System.out.println("No\tLevel\tSalary\tYears\n=============================");
        for(Employee a : objs)
            System.out.printf("%d\t%d\t%d\t%d\n",a.id,a.level,a.salary,a.year);
    }
 
    public Employee(int id, int level, int salary, int year){
        this.id = id;
        this.level = level;
        this.salary = salary;
        this.year = year;
    }
     
    public int id;
    public int level;
    public int salary;
    public int year;
 
    private final static Comparator<Employee> comparator = new Comparator<Employee>(){
        @Override
        public int compare(Employee a1, Employee a2) {
            int cr = 0;
            int a = a2.level - a1.level;
            if(a != 0)
                cr = (a>0)?3:-1;
            else{
                a = a2.salary - a1.salary;
                if(a != 0)
                    cr = (a>0)?2:-2;
                else{
                    a = (int)(a2.year - a1.year);
                    if(a != 0)
                        cr = (a>0)?1:-3;
                }
            }
            return cr;
        }       
    };
     
}

 上面参考方法给出了3级排序规则下的接口实现方法,2级或3级以上的接口实现方式类似。

  • 作者:nuistcc
  • 原文链接:https://blog.csdn.net/nuistcc/article/details/84817453
    更新时间:2022-07-18 12:48:23