Deque 接口中的 addFirst 和 addLast 有什么区别

Question

They seem like behaving in the same way, throwing out the elements in a LIFO pattern.

   Deque<Integer> stack = new ArrayDeque<>();
   for (int i = 0; i <= 10; i++) {
       stack.addFirst(i);
   }
   while(!stack.isEmpty()) {
       System.out.print(stack.removeFirst()+",");
   }

Prints out: 10,9,8,7,6,5,4,3,2,1,0,

   Deque<Integer> stack = new ArrayDeque<>();
   for (int i = 0; i <= 10; i++) {
       stack.addLast(i);
   }
   while(!stack.isEmpty()) {
       System.out.print(stack.removeLast()+",");
   }

Prints out: 10,9,8,7,6,5,4,3,2,1,0,

Answer 1

addFirst in deque means that it will be adding every element at the first position like: lets say there is a variable named "number" and number has 3 elements in it:

number = [10,9,8]

// if i add 7 in it
number = addFirst(7)

output will be like [7,10,9,8] and same in addLast it will add element at the last of the list.

Answer 2

It's is due to your print method being different.

stack.removeFirst()
// ...
stack.removeLast()

On the first case you print them from first to last
On the second case you print them from last to first