Java 中的 ArrayDeque pollFirst()方法
原文:https://www . geeksforgeeks . org/arraydeque-poll first-method-in-Java/
java 中的 java.util.ArrayDeque.pollFirst()方法用于检索或获取并移除 Deque 的第一个元素。peekFirst()方法只检索了第一个元素，但是 pollFirst()也在检索的同时删除了该元素。如果目标为空，则返回空。
语法:
Array_Deque.pollFirst()
参数:该方法不取任何参数。
返回值:该方法删除了 Deque 的第一个元素，并返回相同的值。如果目标为空，则返回空。
下面的程序说明了 Java . util . arraydeque . pollsfirst()方法: 程序 1:
// Java code to illustrate pollFirst()
import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
Deque<String> de_que = new ArrayDeque<String>();
// 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);
// Displaying the first element
System.out.println("The element at head is: " +
de_que.pollFirst());
// Displaying the final ArrayDeque
System.out.println("ArrayDeque after operation: "
+ de_que);
}
}
Output:
ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
The element at head is: Welcome
ArrayDeque after operation: [To, Geeks, 4, Geeks]
程序 2:
// Java code to illustrate pollFirst()
import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
Deque<Integer> de_que = new ArrayDeque<Integer>();
// 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);
// Displaying the first element
System.out.println("The element at head is: " +
de_que.pollFirst());
// Displaying the final ArrayDeque
System.out.println("ArrayDeque after operation: "
+ de_que);
}
}
Output:
ArrayDeque: [10, 15, 30, 20, 5]
The element at head is: 10
ArrayDeque after operation: [15, 30, 20, 5]
程序 3: 对于空车:
// Java code to illustrate pollFirst()
import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
Deque<Integer> de_que = new ArrayDeque<Integer>();
// Displaying the ArrayDeque
System.out.println("ArrayDeque: " + de_que);
// Displaying the first
System.out.println("The element at head is: " +
de_que.pollFirst());
}
}
Output:
ArrayDeque: []
The element at head is: null
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