java - 使用java在同一程序中的升序和降序

Question

我想根据 id 和标记对对数据进行排序。 ID 应按升序排列，标记应按降序排列，这是我的代码:

ArrayList<Student> al=new ArrayList<Student>();
    al.add(new Student(1,"dg",58));
    al.add(new Student(2,"dg",48));
    al.add(new Student(1,"dg",98));
    al.add(new Student(2,"dg",68));
    al.add(new Student(1,"dg",38));
    al.add(new Student(2,"dg",28));
    al.add(new Student(2,"dg",90));    

输出如下:

1 dg 98  
1 dg 58  
1 dg 38  
2 dg 90  
2 dg 68  
2 dg 48  
2 dg 28  

Answer 1

您必须实现 Comparable对于 Student 类或直接使用自定义 Comparator 对其进行排序:

Comparator<Student> comparator = Comparator
    .comparing(Student::getId)                            // First ID in ascending order
    .thenComparing(Comparator.comparing(Student::getMark) // Then mark 
                             .reversed());                // ... but in descending order

al.sort(comparator);                                      // Here is the sort performed