Java Deque peekFirst() 方法

2025 年 3 月 22 日 | 阅读需 2 分钟

Java Deque 接口的 peekFirst() 方法检索但不移除给定双端队列的第一个元素。但是，如果双端队列为空，它可能返回 null。

语法

参数

不适用。

上述方法用于返回给定双端队列的头部元素。另一方面，如果双端队列为空，该方法可能返回 null。

示例 1

import java.util.ArrayDeque;
import java.util.Deque;
public class JavaDequepeekFirstExample1 {
   public static void main(String[] args) {
	   Deque<String> deque = new ArrayDeque<>();
		  deque.offer("Tina");
		  deque.offer("Shyam");
		  deque.offer("Isha");
		  deque.offer("Falguni");
		  String val = deque.peekFirst();
		System.out.println("The first value is given as : "+val);   
		System.out.println("The deque is given as : "+deque);
	}
}

输出

The first value is given as : Tina
The deque is given as : [Tina, Shyam, Isha, Falguni]

示例 2

import java.util.ArrayDeque;
import java.util.Deque;
public class JavaDequepeekFirstExample2 {
    public static void main(String[] args) {
    	Deque<Integer> deque = new ArrayDeque<>();
  	  deque.offer(34);
  	  deque.offer(43);
  	  deque.offer(22);
  	  deque.offer(55);
  	  int val = deque.peekFirst();
  	System.out.println("The first integer value is given as : "+val); 
	System.out.println("The deque is given as : "+deque);
   }   
}

输出

The first integer value is given as : 34
The deque is given as : [34, 43, 22, 55]

示例 3

import java.util.ArrayDeque;
import java.util.Deque;
public class JavaDequepeekFirstExample3 {
   public static void main(String[] args) {
	   Deque<Character> deque = new ArrayDeque<>();
		  deque.offer('H');
		  deque.offer('E');
		  deque.offer('L');
		  deque.offer('L');
		  deque.offer('O');
		  Character val = deque.peekFirst();
		  System.out.println("The first characater value is given as : "+val);
		System.out.println("The final deque is given as : ");    
		for (Character character : deque) {
			System.out.println(character);
	    	}
	     }
	  }

输出

The first characater value is given as : H
The final deque is given as : 
H
E
L
L
O

下一主题Java Deque

Java Deque peekFirst() 方法

语法

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示例 1

示例 2

示例 3

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Java Deque peekFirst() 方法

语法

参数

返回

示例 1

示例 2

示例 3

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