Java 中的 concurrentlinkedequepeek()方法，示例
原文:https://www . geeksforgeeks . org/concurrentlinkedeque-peek-method-in-Java-with-example/
java 中的 Java . util . concurrentlinkedrequest . peek()方法用于检索或获取 Deque 头部的元素。检索到的元素不会被删除或从 Deque 中移除，相反，该方法只是返回它。如果 deque 中没有元素，则返回空值。
语法:
Array_Deque.peek()
参数:该方法不取任何参数。
返回值:该方法返回 Deque 头部的元素。
下面的程序举例说明了 Java . util . concurrentlinkedrequest . peek()方法:
程序 1:
// Java code to illustrate peek()
import java.util.concurrent.*;
public class ConcurrentLinkedDequeDemo {
public static void main(String args[])
{
// Creating an empty ConcurrentLinkedDeque
ConcurrentLinkedDeque<String> de_que
= new ConcurrentLinkedDeque<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 ConcurrentLinkedDeque
System.out.println("Initial ConcurrentLinkedDeque: "
+ de_que);
// Displaying the head
System.out.println("The element at head is: "
+ de_que.peek());
// Displaying the ConcurrentLinkedDeque after operation
System.out.println("Final ConcurrentLinkedDeque: "
+ de_que);
}
}
Output:
Initial ConcurrentLinkedDeque: [Welcome, To, Geeks, 4, Geeks]
The element at head is: Welcome
Final ConcurrentLinkedDeque: [Welcome, To, Geeks, 4, Geeks]
程序 2:
// Java code to illustrate peek()
import java.util.concurrent.*;
public class ConcurrentLinkedDequeDemo {
public static void main(String args[])
{
// Creating an empty ConcurrentLinkedDeque
ConcurrentLinkedDeque<Integer> de_que
= new ConcurrentLinkedDeque<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 ConcurrentLinkedDeque
System.out.println("Initial ConcurrentLinkedDeque: "
+ de_que);
// Displaying the head
System.out.println("The element at head is: "
+ de_que.peek());
// Displaying the ConcurrentLinkedDeque after operation
System.out.println("Final ConcurrentLinkedDeque: "
+ de_que);
}
}
Output:
Initial ConcurrentLinkedDeque: [10, 15, 30, 20, 5]
The element at head is: 10
Final ConcurrentLinkedDeque: [10, 15, 30, 20, 5]
程序 3: 对于空车:
// Java code to illustrate peek()
import java.util.concurrent.*;
public class ConcurrentLinkedDequeDemo {
public static void main(String args[])
{
// Creating an empty ConcurrentLinkedDeque
ConcurrentLinkedDeque<Integer> de_que
= new ConcurrentLinkedDeque<Integer>();
// Displaying the ConcurrentLinkedDeque
System.out.println("ConcurrentLinkedDeque: "
+ de_que);
// Displaying the head
System.out.println("The element at head is: "
+ de_que.peek());
}
}
Output:
ConcurrentLinkedDeque: []
The element at head is: null
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