Java 中的 ArrayDeque peek()方法
原文:https://www . geesforgeks . org/arraydeque-peek-method-in-Java/
java 中的 java.util.ArrayDeque.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队列中移除，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。
下面的程序说明了 Java.util.ArrayDeque.peek()方法: 程序 1:
// Java code to illustrate peek()
import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
ArrayDeque<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("Initial ArrayDeque: " + de_que);
// Displaying the head
System.out.println("The element at head is: " +
de_que.peek());
// Displaying the ArrayDeque after operation
System.out.println("Final ArrayDeque: " + de_que);
}
}
Output:
Initial ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
The element at head is: Welcome
Final ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
程序 2:
// Java code to illustrate peek()
import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
ArrayDeque<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("Initial ArrayDeque: " + de_que);
// Displaying the head
System.out.println("The element at head is: " +
de_que.peek());
// Displaying the ArrayDeque after operation
System.out.println("Final ArrayDeque: " + de_que);
}
}
Output:
Initial ArrayDeque: [10, 15, 30, 20, 5]
The element at head is: 10
Final ArrayDeque: [10, 15, 30, 20, 5]
程序 3: 对于空车:
// Java code to illustrate peek()
import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
ArrayDeque<Integer> de_que = new ArrayDeque<Integer>();
// Displaying the ArrayDeque
System.out.println("ArrayDeque: " + de_que);
// Displaying the head
System.out.println("The element at head is: " + de_que.peek());
}
}
Output:
ArrayDeque: []
The element at head is: null
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