Java中的ArrayDeque addFirst()方法

Java中的Java .util.ArrayDeque.addFirst( Object element ) 方法用于在此双端队列的前面插入特定元素。

句法：

Array_Deque.addFirst(Object element)

参数：参数元素是ArrayDeque类型，指的是要添加的元素。

返回值：该函数不返回任何值。

异常：如果传递的参数为 NULL，该方法将抛出NullPointerException 。

下面的程序说明了Java.util.ArrayDeque.addFirst() 方法：
方案一：

// Java code to illustrate addFirst()
import java.util.*;
  
public class ArrayDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ArrayDeque
        Deque de_que = new ArrayDeque();
  
        // Use add() method to add elements into the Deque
        de_que.add(10);
        de_que.add(15);
        de_que.add(30);
        de_que.add(20);
        de_que.add(5);
  
        // Displaying the ArrayDeque
        System.out.println("ArrayDeque: " + de_que);
  
        // Adding elements at front
        de_que.addFirst(40);
        de_que.addFirst(50);
        de_que.addFirst(60);
        de_que.addFirst(70);
  
        // Displaying the ArrayDeque
        System.out.println("ArrayDeque_front_addition: " + de_que);
  
        // Adding elements using add()
        de_que.add(1);
        de_que.add(2);
        de_que.add(3);
  
        // Displaying the final ArrayDeque
        System.out.println("Final ArrayDeque: " + de_que);
    }
}

输出：

ArrayDeque: [10, 15, 30, 20, 5]
ArrayDeque_front_addition: [70, 60, 50, 40, 10, 15, 30, 20, 5]
Final ArrayDeque: [70, 60, 50, 40, 10, 15, 30, 20, 5, 1, 2, 3]

方案二：

// Java code to illustrate addFirst()
import java.util.*;
  
public class ArrayDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ArrayDeque
        Deque de_que = new ArrayDeque();
  
        // Use add() method to add elements into the Deque
        de_que.add("Welcome");
        de_que.add("To");
        de_que.add("Geeks");
        de_que.add("4");
        de_que.add("Geeks");
  
        // Displaying the ArrayDeque
        System.out.println("ArrayDeque: " + de_que);
  
        // Adding elements at front
        de_que.addFirst("GFG");
        de_que.addFirst("World");
        de_que.addFirst("Hello");
  
        // Displaying the ArrayDeque
        System.out.println("ArrayDeque_front_addition: " + de_que);
  
        // Adding elements using add()
        de_que.add("Coding");
        de_que.add("At");
        de_que.add("BEST");
  
        // Displaying the final ArrayDeque
        System.out.println("Final ArrayDeque: " + de_que);
    }
}

输出：

ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
ArrayDeque_front_addition: [Hello, World, GFG, Welcome, To, Geeks, 4, Geeks]
Final ArrayDeque: [Hello, World, GFG, Welcome, To, Geeks, 4, Geeks, Coding, At, BEST]