Java DelayQueue Class用法及代碼示例

// Java Program Demonstrate DelayQueue
import java.util.concurrent.*;
import java.util.*;
// The DelayObject for DelayQueue
// It must implement Delayed and
// its getDelay() and compareTo() method
class DelayObject implements Delayed {
   
    private String name;
    private long time;
    // Constructor of DelayObject
    public DelayObject(String name, long delayTime)
    {
        this.name = name;
        this.time = System.currentTimeMillis()
                    + delayTime;
    }
    // Implementing getDelay() method of Delayed
    @Override
    public long getDelay(TimeUnit unit)
    {
        long diff = time - System.currentTimeMillis();
        return unit.convert(diff, TimeUnit.MILLISECONDS);
    }
    // Implementing compareTo() method of Delayed
    @Override
    public int compareTo(Delayed obj)
    {
        if (this.time < ((DelayObject)obj).time) {
            return -1;
        }
        if (this.time > ((DelayObject)obj).time) {
            return 1;
        }
        return 0;
    }
    // Implementing toString() method of Delayed
    @Override
    public String toString()
    {
        return "\n{"
            + "name=" + name
            + ", time=" + time
            + "}";
    }
}
// Driver Class
public class GFG {
    public static void main(String[] args)
        throws InterruptedException
    {
        // create object of DelayQueue
        // using DelayQueue() constructor
        BlockingQueue<DelayObject> DQ
            = new DelayQueue<DelayObject>();
        // Add numbers to end of DelayQueue
        DQ.add(new DelayObject("A", 1));
        DQ.add(new DelayObject("B", 2));
        DQ.add(new DelayObject("C", 3));
        DQ.add(new DelayObject("D", 4));
        // print DelayQueue
        System.out.println("DelayQueue: "
                           + DQ);
        // create object of DelayQueue
        // using DelayQueue(Collection c)
        // constructor
        BlockingQueue<DelayObject> DQ2
            = new DelayQueue<DelayObject>(DQ);
        // print DelayQueue
        System.out.println("DelayQueue: "
                           + DQ2);
    }
}

// Java Program Demonstrate DelayQueue methods
import java.util.concurrent.*;
import java.util.*;
// The DelayObject for DelayQueue
// It must implement Delayed and
// its getDelay() and compareTo() method
class DelayObject implements Delayed {
   
    private String name;
    private long time;
    // Constructor of DelayObject
    public DelayObject(String name, long delayTime)
    {
        this.name = name;
        this.time = System.currentTimeMillis()
                    + delayTime;
    }
    // Implementing getDelay() method of Delayed
    @Override
    public long getDelay(TimeUnit unit)
    {
        long diff = time - System.currentTimeMillis();
        return unit.convert(diff, TimeUnit.MILLISECONDS);
    }
    // Implementing compareTo() method of Delayed
    @Override
    public int compareTo(Delayed obj)
    {
        if (this.time < ((DelayObject)obj).time) {
            return -1;
        }
        if (this.time > ((DelayObject)obj).time) {
            return 1;
        }
        return 0;
    }
    // Implementing toString() 
      // method of Delayed
    @Override
    public String toString()
    {
        return "\n{"
            + "name=" + name
            + ", time=" + time
            + "}";
    }
}
// Driver Class
public class GFG {
    public static void main(String[] args)
        throws InterruptedException
    {
        // create object of DelayQueue
        // using DelayQueue() constructor
        BlockingQueue<DelayObject> DQ
            = new DelayQueue<DelayObject>();
        // Add numbers to end of DelayQueue
        // using add() method
        DQ.add(new DelayObject("A", 1));
        DQ.add(new DelayObject("B", 2));
        DQ.add(new DelayObject("C", 3));
        DQ.add(new DelayObject("D", 4));
        // print queue
        System.out.println("DelayQueue: "
                           + DQ);
        // print the head using peek() method
        System.out.println("Head of DelayQueue: "
                           + DQ.peek());
        // print the size using size() method
        System.out.println("Size of DelayQueue: "
                           + DQ.size());
        // remove the head using poll() method
        System.out.println("Head of DelayQueue: "
                           + DQ.poll());
        // print the size using size() method
        System.out.println("Size of DelayQueue: "
                           + DQ.size());
        // clear the DelayQueue using clear() method
        DQ.clear();
        System.out.println("Size of DelayQueue"
                           + " after clear: "
                           + DQ.size());
    }
}

// Java program to illustrate the adding
// elements to the DelayQueue
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;
public class AddingElementsExample {
    public static void main(String args[])
    {
        // Create a DelayQueue instance
        DelayQueue<Delayed> queue
            = new DelayQueue<Delayed>();
        // Create an instance of Delayed
        Delayed obj = new Delayed() {
            public long getDelay(TimeUnit unit)
            {
                return 24; // some value is returned
            }
            public int compareTo(Delayed o)
            {
                if (o.getDelay(TimeUnit.DAYS)
                    > this.getDelay(TimeUnit.DAYS))
                    return 1;
                else if (o.getDelay(TimeUnit.DAYS)
                         == this.getDelay(TimeUnit.DAYS))
                    return 0;
                return -1;
            }
        };
        // Use the add() method to add obj to
        // the empty DelayQueue instance
        queue.add(obj);
        // printing size of the queue to the console
        System.out.println("Size of the queue : "
                           + queue.size());
    }
}

// Java Program to illustrate the removing
// elements of DelayQueue class
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;
public class RemovingElementsExample {
    public static void main(String args[])
    {
        // Create a DelayQueue instance
        DelayQueue<Delayed> queue = new DelayQueue<Delayed>();
        // Create an object of type Delayed
        Delayed ob = new Delayed() {
            public long getDelay(TimeUnit unit)
            {
                return 24; // some value is returned
            }
            public int compareTo(Delayed o)
            {
                if (o.getDelay(TimeUnit.DAYS)
                    > this.getDelay(TimeUnit.DAYS))
                    return 1;
                else if (o.getDelay(TimeUnit.DAYS)
                         == this.getDelay(TimeUnit.DAYS))
                    return 0;
                return -1;
            }
        };
        // Add the object to DelayQueue
        queue.add(ob);
        // Print initial size of Queue
        System.out.println("Initial Size : " + queue.size());
        // Remove the object ob from
        // this DelayQueue
        queue.remove(ob);
        // Print the final size of the DelayQueue
        System.out.println("Size after removing : " + queue.size());
    }
}

// Java Program Demonstrate accessing
// elements of DelayQueue
import java.util.concurrent.*;
import java.util.*;
// The DelayObject for DelayQueue
// It must implement Delayed and
// its getDelay() and compareTo() method
class DelayObject implements Delayed {
    private String name;
    private long time;
    // Constructor of DelayObject
    public DelayObject(String name, long delayTime)
    {
        this.name = name;
        this.time = System.currentTimeMillis() + delayTime;
    }
    // Implementing getDelay() method of Delayed
    @Override public long getDelay(TimeUnit unit)
    {
        long diff = time - System.currentTimeMillis();
        return unit.convert(diff, TimeUnit.MILLISECONDS);
    }
    // Implementing compareTo() method of Delayed
    @Override public int compareTo(Delayed obj)
    {
        if (this.time < ((DelayObject)obj).time) {
            return -1;
        }
        if (this.time > ((DelayObject)obj).time) {
            return 1;
        }
        return 0;
    }
    // Implementing toString() method of Delayed
    @Override public String toString()
    {
        return "\n{"
            + " " + name + ", time=" + time + "}";
    }
}
// Driver Class
public class AccessingElementsExample {
    public static void main(String[] args)
        throws InterruptedException
    {
        // create object of DelayQueue
        // using DelayQueue() constructor
        BlockingQueue<DelayObject> DQ = new DelayQueue<DelayObject>();
        // Add numbers to end of DelayQueue
        // using add() method
        DQ.add(new DelayObject("A", 1));
        DQ.add(new DelayObject("B", 2));
       
        // Print delayqueue
        System.out.println("Original DelayQueue: " + DQ + "\n");
       
        // removing all elements
        DQ.clear();
       
        // peek() method for returning head of the
        // DelayQueue
        System.out.println("Head of the DelayQueue: " + DQ.peek());
    }
}

// Java Program Demonstrate iterating
// over DelayQueue
import java.util.concurrent.*;
import java.util.*;
// The DelayObject for DelayQueue
// It must implement Delayed and
// its getDelay() and compareTo() method
class DelayObject implements Delayed {
    private String name;
    private long time;
    // Constructor of DelayObject
    public DelayObject(String name, long delayTime)
    {
        this.name = name;
        this.time = System.currentTimeMillis() + delayTime;
    }
    // Implementing getDelay() method of Delayed
    @Override public long getDelay(TimeUnit unit)
    {
        long diff = time - System.currentTimeMillis();
        return unit.convert(diff, TimeUnit.MILLISECONDS);
    }
    // Implementing compareTo() method of Delayed
    @Override public int compareTo(Delayed obj)
    {
        if (this.time < ((DelayObject)obj).time) {
            return -1;
        }
        if (this.time > ((DelayObject)obj).time) {
            return 1;
        }
        return 0;
    }
    // Implementing toString() method of Delayed
    @Override public String toString()
    {
        return "\n{"
            + " " + name + ", time=" + time + "}";
    }
}
// Driver Class
public class IteratingExample {
    public static void main(String[] args)
        throws InterruptedException
    {
        // create object of DelayQueue
        // using DelayQueue() constructor
        BlockingQueue<DelayObject> DQ = new DelayQueue<DelayObject>();
        // Add numbers to end of DelayQueue
        // using add() method
        DQ.add(new DelayObject("A", 1));
        DQ.add(new DelayObject("B", 2));
        DQ.add(new DelayObject("C", 3));
        DQ.add(new DelayObject("D", 4));
        // Creating an iterator
        Iterator val = DQ.iterator();
        // print the value after iterating DelayQueue
        System.out.println("The iterator values are: ");
        while (val.hasNext()) {
            System.out.println(val.next());
        }
    }
}