Bael 882 delay queue (#1792)

* BAEL-882 Delay_queue article code

* BAEL-882 Removed println

* BAEL-882 formatting

* BAEL-882 test ordered

core-java/src/main/java/com/baeldung/concurrent/delayqueue/DelayObject.java

@@ -0,0 +1,39 @@
+package com.baeldung.concurrent.delayqueue;
+
+import java.util.concurrent.Delayed;
+import java.util.concurrent.TimeUnit;
+
+public class DelayObject implements Delayed {
+    private String data;
+    private long startTime;
+
+    public DelayObject(String data, long delayInMilliseconds) {
+        this.data = data;
+        this.startTime = System.currentTimeMillis() + delayInMilliseconds;
+    }
+
+    @Override
+    public long getDelay(TimeUnit unit) {
+        long diff = startTime - System.currentTimeMillis();
+        return unit.convert(diff, TimeUnit.MILLISECONDS);
+    }
+
+    @Override
+    public int compareTo(Delayed o) {
+        if (this.startTime < ((DelayObject) o).startTime) {
+            return -1;
+        }
+        if (this.startTime > ((DelayObject) o).startTime) {
+            return 1;
+        }
+        return 0;
+    }
+
+    @Override
+    public String toString() {
+        return "{" +
+                "data='" + data + '\'' +
+                ", startTime=" + startTime +
+                '}';
+    }
+}

core-java/src/main/java/com/baeldung/concurrent/delayqueue/DelayQueueConsumer.java

@@ -0,0 +1,30 @@
+package com.baeldung.concurrent.delayqueue;
+
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.atomic.AtomicInteger;
+
+
+public class DelayQueueConsumer implements Runnable {
+    private BlockingQueue<DelayObject> queue;
+    private final Integer numberOfElementsToTake;
+    public final AtomicInteger numberOfConsumedElements = new AtomicInteger();
+
+    public DelayQueueConsumer(BlockingQueue<DelayObject> queue, Integer numberOfElementsToTake) {
+        this.queue = queue;
+        this.numberOfElementsToTake = numberOfElementsToTake;
+    }
+
+
+    @Override
+    public void run() {
+        for (int i = 0; i < numberOfElementsToTake; i++) {
+            try {
+                DelayObject object = queue.take();
+                numberOfConsumedElements.incrementAndGet();
+                System.out.println("Consumer take: " + object);
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        }
+    }
+}

core-java/src/main/java/com/baeldung/concurrent/delayqueue/DelayQueueProducer.java

@@ -0,0 +1,34 @@
+package com.baeldung.concurrent.delayqueue;
+
+import java.util.UUID;
+import java.util.concurrent.BlockingQueue;
+
+
+public class DelayQueueProducer implements Runnable {
+    private BlockingQueue<DelayObject> queue;
+    private final Integer numberOfElementsToProduce;
+    private final Integer delayOfEachProducedMessageMilliseconds;
+
+    public DelayQueueProducer(BlockingQueue<DelayObject> queue,
+                              Integer numberOfElementsToProduce,
+                              Integer delayOfEachProducedMessageMilliseconds) {
+        this.queue = queue;
+        this.numberOfElementsToProduce = numberOfElementsToProduce;
+        this.delayOfEachProducedMessageMilliseconds = delayOfEachProducedMessageMilliseconds;
+    }
+
+    @Override
+    public void run() {
+        for (int i = 0; i < numberOfElementsToProduce; i++) {
+            DelayObject object
+                    = new DelayObject(UUID.randomUUID().toString(), delayOfEachProducedMessageMilliseconds);
+            System.out.println("Put object = " + object);
+            try {
+                queue.put(object);
+                Thread.sleep(500);
+            } catch (InterruptedException ie) {
+                ie.printStackTrace();
+            }
+        }
+    }
+}