Java中的 Collections.sort() 和示例
Java.util.Collections.sort()方法存在于Java.util.Collections 类中。它用于按升序对指定集合列表中存在的元素进行排序。
它的工作方式类似于Java.util.Arrays.sort() 方法，但它更好，因为它可以对 Array 的元素以及链表、队列以及其中的更多元素进行排序。
public static void sort(List myList)
myList : A List type object we want to sort.
This method doesn't return anything
例子：
Let us suppose that our list contains
{"Geeks For Geeks", "Friends", "Dear", "Is", "Superb"}
After using Collection.sort(), we obtain a sorted list as
{"Dear", "Friends", "Geeks For Geeks", "Is", "Superb"}
按升序对 ArrayList 进行排序
// Java program to demonstrate working of Collections.sort()
import java.util.*;
public class Collectionsorting
{
public static void main(String[] args)
{
// Create a list of strings
ArrayList al = new ArrayList();
al.add("Geeks For Geeks");
al.add("Friends");
al.add("Dear");
al.add("Is");
al.add("Superb");
/* Collections.sort method is sorting the
elements of ArrayList in ascending order. */
Collections.sort(al);
// Let us print the sorted list
System.out.println("List after the use of" +
" Collection.sort() :\n" + al);
}
}
输出：
List after the use of Collection.sort() :
[Dear, Friends, Geeks For Geeks, Is, Superb]
按降序对 ArrayList 进行排序
// Java program to demonstrate working of Collections.sort()
// to descending order.
import java.util.*;
public class Collectionsorting
{
public static void main(String[] args)
{
// Create a list of strings
ArrayList al = new ArrayList();
al.add("Geeks For Geeks");
al.add("Friends");
al.add("Dear");
al.add("Is");
al.add("Superb");
/* Collections.sort method is sorting the
elements of ArrayList in ascending order. */
Collections.sort(al, Collections.reverseOrder());
// Let us print the sorted list
System.out.println("List after the use of" +
" Collection.sort() :\n" + al);
}
}
输出：
List after the use of Collection.sort() :
[Superb, Is, Geeks For Geeks, Friends, Dear]
根据用户定义的标准对 ArrayList 进行排序。
为此，我们可以使用比较器接口。
// Java program to demonstrate working of Comparator
// interface and Collections.sort() to sort according
// to user defined criteria.
import java.util.*;
import java.lang.*;
import java.io.*;
// A class to represent a student.
class Student
{
int rollno;
String name, address;
// Constructor
public Student(int rollno, String name,
String address)
{
this.rollno = rollno;
this.name = name;
this.address = address;
}
// Used to print student details in main()
public String toString()
{
return this.rollno + " " + this.name +
" " + this.address;
}
}
class Sortbyroll implements Comparator
{
// Used for sorting in ascending order of
// roll number
public int compare(Student a, Student b)
{
return a.rollno - b.rollno;
}
}
// Driver class
class Main
{
public static void main (String[] args)
{
ArrayList ar = new ArrayList();
ar.add(new Student(111, "bbbb", "london"));
ar.add(new Student(131, "aaaa", "nyc"));
ar.add(new Student(121, "cccc", "jaipur"));
System.out.println("Unsorted");
for (int i=0; i 输出 ：
Unsorted
111 bbbb london
131 aaaa nyc
121 cccc jaipur
Sorted by rollno
111 bbbb london
121 cccc jaipur
131 aaaa nyc
Arrays.sort() 与 Collections.sort()
Arrays.sort 适用于也可以是原始数据类型的数组。 Collections.sort() 适用于对象集合，如 ArrayList、LinkedList 等。
在创建给定数组项的 ArrayList 后，我们可以使用 Collections.sort() 对数组进行排序。
// Using Collections.sort() to sort an array
import java.util.*;
public class Collectionsort
{
public static void main(String[] args)
{
// create an array of string objs
String domains[] = {"Practice", "Geeks",
"Code", "Quiz"};
// Here we are making a list named as Collist
List colList =
new ArrayList(Arrays.asList(domains));
// Collection.sort() method is used here
// to sort the list elements.
Collections.sort(colList);
// Let us print the sorted list
System.out.println("List after the use of" +
" Collection.sort() :\n" +
colList);
}
}
输出：
List after the use of Collection.sort() :
[Code, Geeks, Practice, Quiz]