閱讀時間: 10分鐘

Collections.sort() method 是在java.util.Collections class之下，是用於元素的排序(默認升序)。
功能與java.util.Arrays.sort() method是差不多。
可以用在所有List的implementations 包括LinkedList 和ArrayList。

Collections.sort() method 有兩個overloaded methods，分別是:
Collections.sort(Collection)
默認升序的方式

Collections.sort(Collection, Comparator)
排序會表按Comparator的方式

例子1:
升序排列

import java.util.*; 

public class Collectionsorting 
{ 
	public static void main(String[] args) 
	{ 
		// 創建一個ArrayList
		ArrayList<String> list1 = new ArrayList<String>(); 
		list1.add("I"); 
		list1.add("am"); 
		list1.add("Martin"); 

		//升序排列
		Collections.sort(list1); 

		//顯示結果
		System.out.println("List after the use of" + " Collection.sort() :\n" +list1); 
	} 
}

例子2:
降序排列

import java.util.*; 

public class Collectionsorting 
{ 
	public static void main(String[] args) 
	{ 
		// 創建一個ArrayList
		ArrayList<String> list1 = new ArrayList<String>(); 
		list1.add("I"); 
		list1.add("am"); 
		list1.add("Martin"); 

		//降序排列
		Collections.sort(list1,Collections.reverseOrder());  

		//顯示結果
		System.out.println("List after the use of" + " Collection.sort() :\n" +list1); 
	} 
}

例子3:
排序會表按Comparator的方式

import java.util.*; 
import java.lang.*; 
import java.io.*; 

// 一個Book的類 
class Book 
{ 
	Int bookID; 
	String name, type; 

	// Constructor 
	public Book (int bookID, String name, 
							String type) 
	{ 
		this. bookID = bookID; 
		this.name = name; 
		this. type = type; 
	} 

	// Book的資料
	public String toString() 
	{ 
		return this. bookID + " " + this.name + 
						" " + this. type; 
	} 
} 

class BookSort implements Comparator<Book> 
{ 
	//以book的ID升序排列
	public int compare(Book a, Book b) 
	{ 
		return a.bookID - b.bookID; 
	} 
} 

class Main 
{ 
	public static void main (String[] args) 
	{ 
		ArrayList< Book > list3 = new ArrayList<Book>(); 
		list3.add(new Book (1234, "Gogogo", "computer")); 
		list3.add(new Book (1698, "Happy", "art")); 
		list3.add(new Book (5468, "Martin", "music")); 

		System.out.println("Unsorted"); 
		for (int i=0; i< list3.size(); i++) 
			System.out.println(list3.get(i)); 

		Collections.sort(list3, new BookSort()); 

		System.out.println("\nBook Sort"); 
		for (int i=0; i< list3.size(); i++) 
			System.out.println(list3.get(i)); 
	} 
}