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Java Deque peekFirst()用法及代码示例


Java Deque 接口的 peekFirst() 方法检索而不是删除给定双端队列的第一个元素。但是，如果双端队列为空，则它可能返回 null。

用法:

public E peekFirst()

参数：

不适用

返回：

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

例子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]

例子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]

例子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




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注：本文由纯净天空筛选整理自 Java Deque peekFirst() Method。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。