Java PriorityBlockingQueue comparator()方法

PriorityBlockingQueue 的 comparator() 方法返回比较器，可以用来对PriorityBlockingQueue中的元素进行排序。如果队列遵循元素的自然排序模式，该方法返回null值。

语法

public Comparator<? super E> comparator()

返回： 该方法返回用于将集合中的元素按特定顺序排序的比较器集合。如果PriorityBlockingQueue遵循默认或自然的排序模式，它将返回一个空值。

下面的程序说明了PriorityBlockingQueue的comparator()方法。

例1： 演示PriorityBlockingQueue的comparator()方法，其中包含一个整数列表。

// Java Program Demonstrate comparator()
// method of PriorityBlockingQueue
  
import java.util.concurrent.PriorityBlockingQueue;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws InterruptedException
    {
  
        // create object of PriorityBlockingQueue
        PriorityBlockingQueue<Integer> PrioQueue
            = new PriorityBlockingQueue<Integer>();
  
        // Add numbers to PriorityBlockingQueue
        PrioQueue.put(45815616);
        PrioQueue.put(4981561);
        PrioQueue.put(4594591);
        PrioQueue.put(9459156);
  
        // get String representation of PriorityBlockingQueue
        String str = PrioQueue.toString();
  
        // Creating a comparator using comparator()
        Comparator comp = PrioQueue.comparator();
  
        // Displaying the comparator values
        System.out.println("Comparator value: " + comp);
  
        if (comp == null)
            System.out.println("PriorityBlockingQueue"
                               + "follows natural ordering");
        else
            System.out.println("PriorityBlockingQueue follows"
                               + comp);
    }
}

输出:

Comparator value: null
PriorityBlockingQueuefollows natural ordering

例子2： 在包含字符串列表的PriorityBlockingQueue上演示toString()方法。

// Java Program Demonstrate comparator()
// method of PriorityBlockingQueue
  
import java.util.concurrent.PriorityBlockingQueue;
import java.util.*;
  
// Comparator to compare Strings
class COMPARING implements Comparator<String> {
    public int compare(String str1, String str2)
    {
        return str2.compareTo(str1);
    }
}
  
public class GFG {
    public static void main(String[] args)
        throws InterruptedException
    {
  
        // define capacity of PriorityBlockingQueue
        int capacityOfQueue = 5;
  
        // create object of PriorityBlockingQueue
        // by passing capacity and comparator class
        // as parameters.
        PriorityBlockingQueue<String> characters
            = new PriorityBlockingQueue<String>(capacityOfQueue,
                                                new COMPARING());
  
        // Add Strings
        characters.add("Geeks");
        characters.add("forGeeks");
        characters.add("A computer portal");
  
        // Getting the comparator using comparator()
        Comparator comp = characters.comparator();
  
        // Displaying the comparator values
        System.out.println("Comparator value is: " + comp);
  
        if (comp == null)
            System.out.println("PriorityBlockingQueue"
                               + "follows natural ordering");
        else
            System.out.println("PriorityBlockingQueue follows: "
                               + comp);
        // display result
        System.out.println("\nThe elements after custom Comparator");
        for (String e : characters)
            System.out.print(e + ", ");
    }
}

输出:

Comparator value is: COMPARING@28d93b30
PriorityBlockingQueue follows: COMPARING@28d93b30

The elements after custom Comparator
forGeeks, Geeks, A computer portal,

参考资料: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/PriorityBlockingQueue.html#comparator-