如何以有效的方式与基于键的对象数组列表进行比较

Question

如何以高效的方式与基于键的对象数组列表进行比较。

我有一组对象 personDetails 和 departmentDetails。

这里我试图根据名为 deptCode 的属性找出两个对象之间的区别。

这是我正在尝试的。

package com.education;

import java.util.*;
import java.util.stream.Collectors;

public class educationMain {

    public static void main(String[] args) {
        
        List<person> list=new ArrayList<person>();  
        person l1 = new person(1,"Samual",100,"Sales","Business");
        person l2 = new person(2,"Alex",100,"Sales","Business");
        person l3 = new person(3,"Bob",101,"Engineering","Technology");
        person l4 = new person(4,"Michel",101,"Engineering","Technology");
        person l5 = new person(5,"Ryan",102,"PR","Services");
        person l6 = new person(6,"Horward",103,"Leadership","Managmnet");
        person l7 = new person(7,"Cyna",104,"HR","Human Resource");
        list.add(l1);  
        list.add(l2);  
        list.add(l3); 
        list.add(l4);  
        list.add(l5);  
        list.add(l6); 
        list.add(l7); 
        
        
        
         List<department> depList = new ArrayList<department>();
         
         
         department d1 = new department(100, "Sales","Business");
         department d2 = new department(101, "Engineering","Technology");
         department d3 = new department(102, "PR","Services");
         depList.add(d1);  
         depList.add(d2);  
         depList.add(d3); 

         List<person> listC = new ArrayList<person>();
         
         
         for(person p : list) {
             boolean  flag = false;
             for (department d:depList) {
                 if(p.deptCode == d.deptCode) {
                     flag = false;
                     break;
                 }else {
                     flag = true;
                 }
             }
             if(flag == true) {
                 listC.add(p);
             }
         }
         
         for(person b:listC){  
             System.out.println(b.personId+" "+b.name+" "+b.deptCode+" "+b.parentDept+" "+b.deptName); 
         }
    }

}

现在打印我想要的东西。但我正在使用两个 for 循环。谁能帮我优化我的代码，因为我在这里使用了两个循环。我想尝试根据某些过滤掉增量的代码。

在 Collection 中我看到 set 可以但不能写那个。佳能帮我优化效率

输出：

6 Horward 103 Leadership Managmnet

 7 Cyna 104 HR Human Resource

Answer 1

给定一个规模为 p 的人员列表和一个规模为 d 的部门列表，您当前的算法的复杂度为 O(p * d)。

您可以将部门 迭代一次 并将他们的部门代码添加到 HashSet<Integer> 并检查每个人的部门代码集 - 复杂性：O(d + p) . 这在计算上更高效，同时需要更多内存——经典的时间与内存权衡：

List<Person> persons = ...;
List<Department> departments = ...

Set<Integer> existingDepartmentIds = new HashSet<>();
for (Department d : departments) {
    existingDepartmentIds.add(d.deptCode); 
}

List<Person> personsWithMatchingDepartmentId = new ArrayList<>();
for (Person p : persons) {
   if (existingDepartmentIds.contains(p.deptCode)) {
       personsWithMatchingDepartmentId.add(p);
   }
}

我以命令式的方式写了这篇文章，因为我不知道您是否精通 Stream 等。功能变体如下所示：

List<Person> persons = ...;
List<Department> departments = ...

Set<Integer> existingDepartmentIds = departments.stream()
   .map(Department::getDeptCode)
   .collect(Collectors.toSet());


List<Person> personsWithMatchingDepartmentId = persons.stream()
    .filter(p -> existingDepartmentIds.contains(p.deptCode))
    .collect(Collectors.toList());

Answer 2

roookeee 已经给出了很好的答案。我的方法大致相同，这是我的实现：

将所有部门添加到列表后，遍历部门，将代码添加到 HashSet。我不确定 class 方法到底是什么，但是，假设它们遵循 JavaBean 约定，它可能看起来像这样：

//Create an instance of HashSet
HashSet<Integer> codeSet = new HashSet<>();

//Iterate over the departments and add the department code to a set.
depList.forEach(dept->{
    codeSet.add(dept.getDeptCode());
  });


List<person> listC = new ArrayList<>();

list.forEach(p->{
    if(!codeSet.contains(p.getDeptCode())){
    listC.add(p);
    }
  });

/**
 *This reads logically as, "For each person, if the set of department codes 
 *DOES NOT contain this persons department code, add them to the list".
 */

请原谅任何糟糕的代码格式，我有一段时间没说 Java 因为我一直在努力学习 Python。另外，我没有专业的编程经验，我只是一个自认为编码很整洁的少年，所以，不要把我的话当作福音。

如何以有效的方式与基于键的对象数组列表进行比较

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