java - 我如何使用 foreach 循环来打印不同类的不同对象的Arraylist

Question

class Main
{
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);

        Loan loan = new Loan();
        Date date = new Date();
        Strings strings = new Strings();
        Frame frame = new Frame();
        Circle circle = new Circle();

        ArrayList<Object> mylist = new ArrayList<Object>();
        mylist.add(loan);
        mylist.add(date);
        mylist.add(strings);
        mylist.add(frame);
        mylist.add(circle);

        for (Object i : mylist)
        {
            System.out.println(mylist.get(i));
        }
         /*
         //this method is working fine
         System.out.println(mylist.get(0));
         System.out.println(mylist.get(1));
         System.out.println(mylist.get(2));
         System.out.println(mylist.get(3));
         System.out.println(mylist.get(4));

         //this method is also working fine
         for (int i = 0; i < 4; i++)
         {
            System.out.println(mylist.get(i));
         }*/

    }
}

My Arraylist is of diiferent object types and all have fields with values and a toString method in each class (so that the printing is possible).....If i dont use a loop and if i use an iterating loop its working fine but i want to use a for each loop i used the above syntax but its showing errors.

Answer 1

myList.forEach(System.out::println); 

并且不要将 myList 声明为 ArrayList，而仅声明为 List - 更喜欢在可用时将变量声明为接口(interface)