如何使用Comparator对ArrayList进行排序？ [英] How to sort ArrayList using Comparator?

问题描述

我有一个类学生实现一个静态方法

  public static Comparator< Student> getCompByName（）
  

返回学生的一个新比较器对象，比较2学生对象

我现在需要通过使用我的函数getCompByName（）将学生的ArrayList按'name'排序来测试这个。 b

这是我的Student类中的我的Comparator方法。

  public static Comparator< Student> getCompByName（）
 {
 Comparator comp = new Comparator< Student>（）{
 @Override 
 public int compare（Student s1，Student s2）
 {
 return s1.name.compareTo（s2.name）; 
} 
}; 
 return comp; 
} 
  

和主要我需要测试

  public static void main（String [] args）
 {
 //这里的TODO代码应用逻辑
 
 / / --------学生阶级测试-------------------------------------- ----- 
 ArrayList< Student> students = new ArrayList（）; 
学生s1 =新学生（Mike）; 
学生s2 =新学生（Hector）; 
学生s3 =新学生（Reggie）; 
学生s4 =新学生（zark）; 
 students.add（s1）; 
 students.add（s2）; 
 students.add（s3）; 
 students.add（S4）; 
 
 //使用学生类中的getCompByName（）对学生进行排序
  

任何人告诉我如何使用getCompByName（）在我的主要实际按名称排序ArrayList？对比较者来说是新的，并且很难与他们的用法。该方法返回一个比较器，所以我不知道这将如何实现。我知道我需要使用getCompByName（）来排序，我只是不知道如何实现它。

解决方案

href =http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#sort%28java.util.List,%20java.util.Comparator%29> Collections.sort （List，Comparator）方法：

  Collections.sort（students，Student.getCompByName（））; 
  

在你的代码中，使用 List 列表：

  ; students = new ArrayList（）; 
  

您还可以使用 Student [] 并将其传递给 ArrayList 构造函数：

  public static void main（String [] args）{
 Student [] studentArr = new Student [] {new student（Mike），new Student（Hector），new Student（Reggie），new学生（zark）}; 
 List< Student> students = new ArrayList< Student>（Arrays.asList（studentArr））; 
 Collections.sort（students，Student.getCompByName（））; 
 
 for（Student student：students）{
 System.out.println（student.getName（））; 
} 
} 
  

这里是全文来源。

I have a Class Student that Implements a static method

public static Comparator<Student> getCompByName()

that returns a new comparator object for Student that compares 2 Students objects by the attribute 'name'.

I need to now test this by sorting a students ArrayList by 'name' using my function getCompByName().

Here is my Comparator method in my Student class.

public static Comparator<Student> getCompByName()
{   
 Comparator comp = new Comparator<Student>(){
     @Override
     public int compare(Student s1, Student s2)
     {
         return s1.name.compareTo(s2.name);
     }        
 };
 return comp;
}  

And Main where I need to test

public static void main(String[] args)
{
    // TODO code application logic here

    //--------Student Class Test-------------------------------------------
    ArrayList<Student> students = new ArrayList();
    Student s1 = new Student("Mike");
    Student s2 = new Student("Hector");
    Student s3 = new Student("Reggie");
    Student s4 = new Student("zark");
    students.add(s1);
    students.add(s2);
    students.add(s3);
    students.add(S4);

    //Use getCompByName() from Student class to sort students

Can anyone show me how I would use the getCompByName() in my main to actually sort the ArrayList by name? Im new to comparators and having a hard time with their usages. The method returns a comparator, so Im not sure how this will be implemented. I know I need to use getCompByName() to sort, im just not sure how to implement it.

解决方案

Use the Collections.sort(List, Comparator) method:

Collections.sort(students, Student.getCompByName());

Also in your code it would be good to use the List interface when declaring the List:

List<Student> students = new ArrayList();

You could also tighten up the code by using a Student[] and passing it to the ArrayList constructor:

public static void main(String[] args) {
    Student[] studentArr = new Student[]{new Student("Mike"),new Student("Hector"), new Student("Reggie"),new Student("zark")};
    List<Student> students = new ArrayList<Student>(Arrays.asList(studentArr));
    Collections.sort(students, Student.getCompByName());

    for(Student student:students){
        System.out.println(student.getName());
    }
}

Here is a Gist of the full source.

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