创建对象的列表/数组列表并对列表进行排序（Java）[重复]

Question

可能重复：
Sorting an ArrayList of Contacts based on name?

我有一个学生对象，然后我创建 ArrayList 并将学生添加到列表中。

ArrayList<Student_Object> studentsList = new ArrayList<>();

现在，我想按 studentId fleid 对列表进行排序。我该怎么做？

有没有更好的解决方案？谢谢

---

所以我在 Student _Object 类中有这个方法

班级是：

class Student_Object implements Comparator<Student_Object>

方法是：

public int compare(Student_Object student1, Student_Object student2){
    String student1TUID = student1.getTUID();        
    String student2TUID = student2.getTUID();

return student1TUID.compareTo(student2TUID);   


}

从哪里运行语句？

Collections.sort(studentsList);

如果我从我的主类运行它，我会在 netbeans 中得到错误：

no suitable method found for sort(ArrayList<Student_Object>)
    method Collections.<T#1>sort(List<T#1>,Comparator<? super T#1>) is not applicable
      (cannot instantiate from arguments because actual and formal argument lists differ in length)
    method Collections.<T#2>sort(List<T#2>) is not applicable
      (inferred type does not conform to declared bound(s)
        inferred: Student_Object
        bound(s): Comparable<? super Student_Object>)
  where T#1,T#2 are type-variables:
    T#1 extends Object declared in method <T#1>sort(List<T#1>,Comparator<? super T#1>)
    T#2 extends Comparable<? super T#2> declared in method <T#2>sort(List<T#2>)
----
(Alt-Enter shows hints)

---

让它工作。我用 Collections.sort(studentsList, new Student_Object());

谢谢大家

Answer 1

一种方法是：

编写comparator 并覆盖compare 方法。然后通过比较器使用Collections.sort()。

例子：

class StudentComparator implements Comparator<Student> {

    public int compare(Student stud1, Student stud2){

        int stu1ID = stud1.getId();       
        int stu2ID = stud2.getId();

        if(stu1ID > stu2ID)
            return 1;
        else if(stu1ID < st21ID )
            return -1;
        else
            return 0;    
    }

}

另一种口味可能是：

 class StudentComparator implements Comparator<Student> {

        public int compare(Student stud1, Student stud2){

            int stu1ID = stud1.getId();       
            int stu2ID = stud2.getId();

           return stud1ID-stu2ID;
        }

    }

这个tutorial 可以帮助你。

Answer 2

要进行排序，您需要实现Comparable 接口。我还强烈建议您在其中实现 equals 和 hashCode。示例：

public class Student implements Comparable  
{  
    private String name;  
    private int id;  
    ...

    public int compareTo(Student otherStudent)  
    {  
       if(this.id < otherStudent.id)  
       {  
          return -1;
       }  
       else if(this.id > otherStudent.id)  
       {  
           return 1;
       }  
        else{
           return 0;  
        }  

    }  
}