BAEL-1456 - How to implement task prioritization in Java (#3366)

* priority based job execution in java

* minor fixes

* updated to use java 8 features

core-java-concurrency/src/test/java/com/baeldung/concurrent/prioritytaskexecution/PriorityJobSchedulerUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.concurrent.prioritytaskexecution;
+
+import org.junit.Test;
+
+public class PriorityJobSchedulerUnitTest {
+    private static int POOL_SIZE = 1;
+    private static int QUEUE_SIZE = 10;
+    
+    @Test
+    public void whenMultiplePriorityJobsQueued_thenHighestPriorityJobIsPicked() {
+        Job job1 = new Job("Job1", JobPriority.LOW);
+        Job job2 = new Job("Job2", JobPriority.MEDIUM);
+        Job job3 = new Job("Job3", JobPriority.HIGH);
+        Job job4 = new Job("Job4", JobPriority.MEDIUM);
+        Job job5 = new Job("Job5", JobPriority.LOW);
+        Job job6 = new Job("Job6", JobPriority.HIGH);
+        
+        PriorityJobScheduler pjs = new PriorityJobScheduler(POOL_SIZE, QUEUE_SIZE);
+        
+        pjs.scheduleJob(job1);
+        pjs.scheduleJob(job2);
+        pjs.scheduleJob(job3);
+        pjs.scheduleJob(job4);
+        pjs.scheduleJob(job5);
+        pjs.scheduleJob(job6);
+        
+        // ensure no tasks is pending before closing the scheduler
+        while (pjs.getQueuedTaskCount() != 0);
+        
+        // delay to avoid job sleep (added for demo) being interrupted
+        try {
+            Thread.sleep(2000);
+        } catch (InterruptedException ignored) {
+        }
+        
+        pjs.closeScheduler();
+    }
+}