Java LinkedBlockingQueue peek()用法及代码示例

LinkedBlockingQueue的peek()方法返回LinkedBlockingQueue的头。它检索LinkedBlockingQueue头的值，但不删除它。如果LinkedBlockingQueue为空，则此方法返回null。

用法:

public E peek()

返回值：此方法返回LinkedBlockingQueue的头部。

以下示例程序旨在说明LinkedBlockingQueue类的peek()方法：

示例1:使用peek()方法返回LinkedBlockingQueue的头，其中容量7的LinkedBlockingQueue包含名称列表

// Java Program Demonstrate peek() 
// method of LinkedBlockingQueue 
  
import java.util.concurrent.LinkedBlockingQueue; 
public class GFG { 
  
    public static void main(String[] args) 
    { 
        // define capacity of LinkedBlockingQueue 
        int capacityOfQueue = 7; 
  
        // create object of LinkedBlockingQueue 
        LinkedBlockingQueue<String> linkedQueue 
            = new LinkedBlockingQueue<String>(capacityOfQueue); 
  
        // Add element to LinkedBlockingQueue 
        linkedQueue.add("John"); 
        linkedQueue.add("Tom"); 
        linkedQueue.add("Clark"); 
        linkedQueue.add("Kat"); 
  
        // find head of linkedQueue using peek() method 
        String head = linkedQueue.peek(); 
  
        // print result 
        System.out.println("Queue is " + linkedQueue); 
  
        // print head of queue 
        System.out.println("Head of Queue is " + head); 
  
        // removing one element 
        linkedQueue.remove(); 
  
        // again get head of queue 
        head = linkedQueue.peek(); 
  
        // print result 
        System.out.println("\nRemoving one element from Queue\n"); 
        System.out.println("Queue is " + linkedQueue); 
  
        // print head of queue 
        System.out.println("Head of Queue is " + head); 
    } 
}

输出：

Queue is [John, Tom, Clark, Kat]
Head of Queue is John

Removing one element from Queue

Queue is [Tom, Clark, Kat]
Head of Queue is Tom

示例2:查找包含员工列表的LinkedBlockingQueue的头

// Java Program Demonstrate peek() 
// method of LinkedBlockingQueue 
  
import java.util.concurrent.LinkedBlockingQueue; 
public class GFG { 
  
    public void findPeek() 
    { 
        // define capacity of LinkedBlockingQueue 
        int capacityOfQueue = 7; 
  
        // create object of LinkedBlockingQueue 
        LinkedBlockingQueue<Employee> linkedQueue 
            = new LinkedBlockingQueue<Employee>(capacityOfQueue); 
  
        // Add element to LinkedBlockingQueue 
        Employee emp1 = new Employee("Ravi", "Tester", "39000"); 
        Employee emp2 = new Employee("Sanjeet", "Manager", "98000"); 
  
        // Add Employee Objects to linkedQueue 
        linkedQueue.add(emp1); 
        linkedQueue.add(emp2); 
  
        // print head then remove element 
        // and follow same process again 
        // until the queue becomes empty 
  
        while (linkedQueue.size() != 0) { 
  
            // find head of linkedQueue using peek() method 
            Employee head = linkedQueue.peek(); 
  
            // print results 
            System.out.println("Head of list"); 
            System.out.println("Employee Name : " + head.name); 
            System.out.println("Employee Position : " + head.position); 
            System.out.println("Employee Salary : " + head.salary); 
  
            linkedQueue.remove(); 
            if (linkedQueue.size() != 0) 
                System.out.println("\nRemoving one element from Queue\n"); 
        } 
    } 
  
    // create an Employee Object with 
    // position and salary as an attribute 
    public class Employee { 
  
        public String name; 
        public String position; 
        public String salary; 
        Employee(String name, String position, String salary) 
        { 
            this.name = name; 
            this.position = position; 
            this.salary = salary; 
        } 
        @Override
        public String toString() 
        { 
            return "Employee [name=" + name + ", position="
                + position + ", salary=" + salary + "]"; 
        } 
    } 
    // Main Method 
    public static void main(String[] args) 
    { 
        GFG gfg = new GFG(); 
        gfg.findPeek(); 
    } 
}

输出：

Head of list
Employee Name : Ravi
Employee Position : Tester
Employee Salary : 39000

Removing one element from Queue

Head of list
Employee Name : Sanjeet
Employee Position : Manager
Employee Salary : 98000

参考： https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/LinkedBlockingQueue.html#peek–

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