Método DelayQueue peek() en Java con ejemplos

El método peek() de DelayQueue se usa para recuperar el encabezado de DelayQueue, pero no lo elimina, como en el caso del método poll() donde el encabezado se elimina de DelayQueue.

Sintaxis: 

public E peek ()

Parámetros: 
Este método no acepta ningún parámetro.

Devoluciones: 
este método devuelve el encabezado de DelayQueue y no lo elimina de esta DelayQueue.

Excepción:  
puntero nulo Excepción: si el encabezado no está presente, esta función devolverá un valor nulo.

Debajo del programa para ilustrar DelayQueue peek() en Java:

Ejemplo 1:  

// Java Program Demonstrate DelayQueue peek() method
 
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 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 delayqueue
        System.out.println("Original DelayQueue: "
                           + DQ + "\n");
        // peek() method for returning head of the DelayQueue
 
        System.out.println("Head of the DelayQueue: "
                           + DQ.peek());
        // print DelayQueue
        System.out.println("\nAfter peek() method, DelayQueue: "
                           + DQ);
    }
}

Original DelayQueue: [
{ A, time=1545817334485}, 
{ B, time=1545817334486}, 
{ C, time=1545817334487}, 
{ D, time=1545817334488}]

Head of the DelayQueue: 
{ A, time=1545817334485}

After peek() method, DelayQueue: [
{ A, time=1545817334485}, 
{ B, time=1545817334486}, 
{ C, time=1545817334487}, 
{ D, time=1545817334488}]

Ejemplo 2: 

// Java Program Demonstrate DelayQueue peek() method
 
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 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));
        // 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());
    }
}

Original DelayQueue: [
{ A, time=1545817342666}, 
{ B, time=1545817342667}]

Head of the DelayQueue: null