Java LinkedBlockingQueue size()用法及代碼示例

LinkedBlockingQueue的size()方法返回LinkedBlockingQueue包含的元素數。當隊列為空隊列時，size()返回0，而當隊列已滿時，size()返回隊列的容量。

用法:

public int size()

返回值：此方法返回該時刻LinkedBlockingQueue中的元素數。返回類型為int。

以下示例程序旨在說明LinkedBlockingQueue類的size()方法：

示例1:使用size()在隊列的每個操作打印大小之後在LinkedBlockingQueue上執行添加和刪除操作

// Java Program Demonstrate size() 
// method of LinkedBlockingQueue 
  
import java.util.concurrent.LinkedBlockingQueue; 
  
public class GFG { 
  
    public static void main(String[] args) 
        throws InterruptedException 
    { 
        // define capacity of LinkedBlockingQueue 
        int capacityOfQueue = 4; 
  
        // create object of LinkedBlockingQueue 
        LinkedBlockingQueue<String> linkedQueue 
            = new LinkedBlockingQueue<String>(capacityOfQueue); 
  
        // Add element using put() method 
        linkedQueue.put("Karan"); 
        linkedQueue.put("Suraj"); 
  
        // get size of queue using size() method 
        int size = linkedQueue.size(); 
  
        // print elements of queue and size of queue 
        System.out.println("Items in Queue are " + linkedQueue); 
        System.out.println("Size of Queue is " + size); 
  
        // add more elements 
        linkedQueue.put("Harsh"); 
        linkedQueue.put("Rahul"); 
  
        // get size of queue using size() method 
        size = linkedQueue.size(); 
  
        // print elements of queue and size of queue 
        System.out.println("Items in Queue are " + linkedQueue); 
        System.out.println("Size of Queue is " + size); 
  
        // try to remove element fom Queue 
        boolean try1 = linkedQueue.remove("Karan"); 
        System.out.println("String name Karan is removed :"
                           + try1); 
  
        // get size of queue using size() method 
        size = linkedQueue.size(); 
  
        // print elements of queue and size of queue 
        System.out.println("Items in Queue are " + linkedQueue); 
        System.out.println("Size of Queue is " + size); 
    } 
}

輸出：

Items in Queue are [Karan, Suraj]
Size of Queue is 2

Items in Queue are [Karan, Suraj, Harsh, Rahul]
Size of Queue is 4

String name Karan is removed :true
Items in Queue are [Suraj, Harsh, Rahul]
Size of Queue is 3

示例2:使用size()在包含員工對象的LinkedBlockingQueue上執行添加和刪除操作，在每次操作後打印隊列大小

// Java Program Demonstrate size() 
// method of LinkedBlockingQueue 
  
import java.util.Iterator; 
import java.util.concurrent.LinkedBlockingQueue; 
  
public class GFG { 
  
    public void sizeDemo() throws InterruptedException 
    { 
        // define capacity of LinkedBlockingQueue 
        int capacityOfQueue = 5; 
  
        // create object of LinkedBlockingQueue 
        LinkedBlockingQueue<Employee> linkedQueue 
            = new LinkedBlockingQueue<Employee>(capacityOfQueue); 
  
        // get size of queue using size() method 
        int size = linkedQueue.size(); 
        System.out.println("Size of Queue " + size); 
  
        // Add element to LinkedBlockingQueue 
        Employee emp1 = new Employee("Ranjeet", "Tester", "29000", 27); 
        Employee emp2 = new Employee("Sanjeet", "Manager", "98000", 34); 
        Employee emp3 = new Employee("Karan", "Analyst", "44000", 30); 
  
        // Add Employee Objects to linkedQueue 
        // Using put(E e) 
        linkedQueue.put(emp1); 
        linkedQueue.put(emp2); 
        linkedQueue.put(emp3); 
  
        // print details of linkedQueue 
        System.out.println("\nAfter Adding some Elements queue has"); 
        Iterator itr = linkedQueue.iterator(); 
        while (itr.hasNext()) 
            System.out.println(itr.next()); 
  
        // get size of queue using size() method 
        size = linkedQueue.size(); 
        System.out.println("\nAfter Adding Size of Queue " + size); 
  
        // remove employee2 name Sanjeet and Ranjeet from linkedQueue 
        linkedQueue.remove(emp2); 
        linkedQueue.remove(emp1); 
  
        // print details of linkedQueue 
        System.out.println("\nAfter removing Some Elements"); 
        itr = linkedQueue.iterator(); 
        while (itr.hasNext()) 
            System.out.println(itr.next()); 
  
        // get size of queue using size() method 
        size = linkedQueue.size(); 
        System.out.println("\nAfter removing size of Queue " + size); 
    } 
  
    // create an Employee Object with name, 
    // position, salary and age as attributes 
    public class Employee { 
  
        public String name; 
        public String position; 
        public String salary; 
        public int Age; 
  
        Employee(String name, String position, 
                 String salary, int age) 
        { 
            this.name = name; 
            this.position = position; 
            this.salary = salary; 
            this.Age = age; 
        } 
  
        @Override
        public String toString() 
        { 
            return "Employee [name=" + name + ", position="
                + position + ", salary=" + salary + ", Age=" + Age + "]"; 
        } 
    } 
  
    // Main Method 
    public static void main(String[] args) 
    { 
        GFG gfg = new GFG(); 
        try { 
            gfg.sizeDemo(); 
        } 
        catch (InterruptedException e) { 
            // TODO Auto-generated catch block 
            e.printStackTrace(); 
        } 
    } 
}

輸出：

Size of Queue 0

After Adding some Elements queue has
Employee [name=Ranjeet, position=Tester, salary=29000, Age=27]
Employee [name=Sanjeet, position=Manager, salary=98000, Age=34]
Employee [name=Karan, position=Analyst, salary=44000, Age=30]

After Adding Size of Queue 3

After removing Some Elements
Employee [name=Karan, position=Analyst, salary=44000, Age=30]

After removing size of Queue 1

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

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