BAEL-1071 Runnable vs Callable in Java (#2513)

core-java-concurrency/src/main/java/com/baeldung/concurrent/callable/FactorialTask.java

@@ -0,0 +1,30 @@
+package com.baeldung.concurrent.callable;
+
+
+import java.util.concurrent.Callable;
+
+public class FactorialTask implements Callable<Integer> {
+    int number;
+
+    public FactorialTask(int number) {
+        this.number = number;
+    }
+
+    public Integer call() throws InvalidParamaterException {
+        int fact=1;
+        if(number < 0)
+            throw new InvalidParamaterException("Number must be positive");
+
+        for(int count=number;count>1;count--){
+            fact=fact * count;
+        }
+
+        return fact;
+    }
+
+    private class InvalidParamaterException extends Exception {
+        public InvalidParamaterException(String message) {
+            super(message);
+        }
+    }
+}

core-java-concurrency/src/test/java/com/baeldung/concurrent/callable/FactorialTaskManualTest.java

@@ -0,0 +1,48 @@
+package com.baeldung.concurrent.callable;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+
+import static junit.framework.Assert.assertEquals;
+
+public class FactorialTaskManualTest {
+
+    private ExecutorService executorService;
+
+    @Before
+    public void setup(){
+        executorService = Executors.newSingleThreadExecutor();
+    }
+
+    @Test
+    public void whenTaskSubmitted_ThenFutureResultObtained() throws ExecutionException, InterruptedException {
+        FactorialTask task = new FactorialTask(5);
+        Future<Integer> future= executorService.submit(task);
+        assertEquals(120,future.get().intValue());
+    }
+
+    @Test(expected = ExecutionException.class)
+    public void whenException_ThenCallableThrowsIt() throws ExecutionException, InterruptedException {
+        FactorialTask task = new FactorialTask(-5);
+        Future<Integer> future= executorService.submit(task);
+        Integer result=future.get().intValue();
+    }
+
+    @Test
+    public void whenException_ThenCallableDoesntThrowsItIfGetIsNotCalled(){
+        FactorialTask task = new FactorialTask(-5);
+        Future<Integer> future= executorService.submit(task);
+        assertEquals(false,future.isDone());
+    }
+
+    @After
+    public void cleanup(){
+        executorService.shutdown();
+    }
+}