ArrayList集合對象的sort()方法

public void sort(Comparator<? super E> c)
Parameters:c - the Comparator used to compare list elements. A null value indicates that the elements' natural ordering should be used

上面說明形參是實現Comparator接口的類對象，如果為null，則ArrayList集合的元素就按自然順序來排序

代碼驗證如下：

import java.util.*;

public class Demo12{        
    public static void main(String[] args)throws Exception{  
        
        List<Integer> list = new ArrayList<>();
        list.add(94);
        list.add(45);
        list.add(28);
        list.add(58);
        
        list.sort(null);
        //遍歷list集合元素
        for(int i:list){
            System.out.print(i + "\t");
        }
        
        System.out.println();
        
        //轉換為數組打印出來看看
        System.out.println(Arrays.toString(list.toArray()));        
    }
}