**试用java内置的栈数据结构**
```
// "static void main" must be defined in a public class.
public class Main {
public static void main(String[] args) {
// 1. Initialize a stack.
Stack<Integer> s = new Stack<>();
// 2. Push new element.
s.push(5);
s.push(13);
s.push(8);
s.push(6);
// 3. Check if stack is empty.
if (s.empty() == true) {
System.out.println("Stack is empty!");
return;
}
// 4. Pop an element.
s.pop();
// 5. Get the top element.
System.out.println("The top element is: " + s.peek());
// 6. Get the size of the stack.
System.out.println("The size is: " + s.size());
}
}
```
