Refactor code for improved readability and exception handling

Author: Rakesh Venkatesh

multithreading/src/main/java/com/rakeshv/completablefutures/AsyncExample.java

@@ -63,7 +63,7 @@ public static void main(String[] args) {
                 emailFuture,
                 (users, emails) -> {
                     System.out.println("User size is " + users.size() + " and email size is " + emails.size());
-        });
+                });
 
         start.completeAsync(() -> null, starter);
         CompletableFuture<List<User>> users1 = completableFuture.thenComposeAsync(fetchUsers);
@@ -81,13 +81,14 @@ public static void main(String[] args) {
             executorService1.shutdown();
             starter.shutdown();
         } catch (Exception e) {
-            //TODO: handle exception
+            e.printStackTrace();
         }
     }
 
     public static void sleep(long millis) {
         try {
             Thread.sleep(millis);
-        } catch (Exception e) {}
+        } catch (Exception e) {
+        }
     }
 }

multithreading/src/main/java/com/rakeshv/completablefutures/BmiCalculator.java

@@ -11,42 +11,44 @@
 
 public class BmiCalculator {
     ExecutorService executorService = Executors.newFixedThreadPool(2);
+
     public static void main(String[] args) throws InterruptedException, ExecutionException {
         BmiCalculator bmiCalculator = new BmiCalculator();
 
-        Scanner scanner = new Scanner(System.in);
-
-        System.out.println("Please enter the weight");
-        double weight = Double.parseDouble(scanner.nextLine());
-        System.out.println("Please enter the height");
-        double height = Double.parseDouble(scanner.nextLine());
-        CompletableFuture<Double> getHeight = supplyAsync(() -> {
-            if (height <= 0) {
-                throw new IllegalArgumentException("Height cant be 0");
-            }
-            return height;
-        },bmiCalculator.executorService).exceptionally(ex -> {
-            System.out.println("Invalid height entered. so considering height as 1m");
-            return 1.0;
-        });
-
-        CompletableFuture<Double> getWeight = supplyAsync(() -> {
-            if (weight <= 0) {
-                throw new IllegalArgumentException("Weight cant be 0");
-            }
-            return weight;
-        }, bmiCalculator.executorService).exceptionally(ex -> {
-            System.out.println("Invalid weight entered. so considering weight as 1kg");
-            return 1.0;
-        });
-
-        System.out.println("Calculating BMI");
-        TimeUnit.SECONDS.sleep(2);
-
-        CompletableFuture<Double> bmiFuture = getHeight
-                .thenCombineAsync(getWeight, (h, w) -> bmiCalculator.getBmi(w, h));
-
-        System.out.println(bmiFuture.get());
+        try (Scanner scanner = new Scanner(System.in)) {
+            System.out.println("Please enter the weight");
+            double weight = Double.parseDouble(scanner.nextLine());
+            System.out.println("Please enter the height");
+            double height = Double.parseDouble(scanner.nextLine());
+
+            CompletableFuture<Double> getHeight = supplyAsync(() -> {
+                if (height <= 0) {
+                    throw new IllegalArgumentException("Height cant be 0");
+                }
+                return height;
+            }, bmiCalculator.executorService).exceptionally(ex -> {
+                System.out.println("Invalid height entered. so considering height as 1m");
+                return 1.0;
+            });
+
+            CompletableFuture<Double> getWeight = supplyAsync(() -> {
+                if (weight <= 0) {
+                    throw new IllegalArgumentException("Weight cant be 0");
+                }
+                return weight;
+            }, bmiCalculator.executorService).exceptionally(ex -> {
+                System.out.println("Invalid weight entered. so considering weight as 1kg");
+                return 1.0;
+            });
+
+            System.out.println("Calculating BMI");
+            TimeUnit.SECONDS.sleep(2);
+
+            CompletableFuture<Double> bmiFuture = getHeight
+                    .thenCombineAsync(getWeight, (h, w) -> bmiCalculator.getBmi(w, h));
+
+            System.out.println(bmiFuture.get());
+        }
         bmiCalculator.executorService.shutdownNow();
     }
 

multithreading/src/main/java/com/rakeshv/completablefutures/CompletableFutureDemo.java

@@ -11,12 +11,11 @@ public static void main(String[] args) {
 
         Runnable runnable = () -> {
             System.out.println("Executing from thread " +
-             Thread.currentThread().getName());
+                    Thread.currentThread().getName());
         };
 
-        CompletableFuture completableFuture =
-            CompletableFuture.runAsync(runnable, executorService);
-        
+        CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(runnable, executorService);
+
         System.out.println("From main");
         completableFuture.join();
 
@@ -29,15 +28,17 @@ public static void main(String[] args) {
         Supplier<String> delayedSupplier = () -> {
             try {
                 Thread.sleep(3000);
-            } catch (Exception e) {}
+            } catch (Exception e) {
+            }
 
             return "sleep complete";
         };
 
         CompletableFuture<String> longFuture = CompletableFuture.supplyAsync(delayedSupplier, executorService);
         try {
             Thread.sleep(1000);
-        } catch (Exception e) {}
+        } catch (Exception e) {
+        }
 
         System.err.print("He is taking long time to complete");
         longFuture.complete("He's dead jim");

multithreading/src/main/java/com/rakeshv/completablefutures/HttpClientExample.java

@@ -1,6 +1,5 @@
 package com.rakeshv.completablefutures;
 
-import java.io.IOException;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.net.http.HttpClient;
@@ -12,7 +11,8 @@
 import java.util.stream.Collectors;
 
 public class HttpClientExample {
-    public static void main(String[] args) throws InterruptedException, ExecutionException, TimeoutException, URISyntaxException {
+    public static void main(String[] args)
+            throws InterruptedException, ExecutionException, TimeoutException, URISyntaxException {
         ExecutorService service = Executors.newFixedThreadPool(5);
 
         HttpClient client = HttpClient.newBuilder()
@@ -24,8 +24,7 @@ public static void main(String[] args) throws InterruptedException, ExecutionExc
                 new URI("https://www.google.com"),
                 new URI("https://www.facebook.com"),
                 new URI("https://www.netflix.com"),
-                new URI("https://www.twitter.com")
-        );
+                new URI("https://www.twitter.com"));
 
         List<CompletableFuture<String>> result = links.stream()
                 .map(url -> {

multithreading/src/main/java/com/rakeshv/demo1/Demo1.java

@@ -25,10 +25,8 @@ public static void main(String[] args) {
             try {
                 System.out.println(result.get());
             } catch (InterruptedException e) {
-                // TODO Auto-generated catch block
                 e.printStackTrace();
             } catch (ExecutionException e) {
-                // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
@@ -40,15 +38,12 @@ public static void main(String[] args) {
         try {
             System.out.println(completableFuture.get());
         } catch (InterruptedException e) {
-            // TODO Auto-generated catch block
             e.printStackTrace();
         } catch (ExecutionException e) {
-            // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }
 
-    
 }
 
 class Runner extends Thread {

multithreading/src/main/java/com/rakeshv/demo2/Process.java

@@ -8,21 +8,24 @@ public static void main(String[] args) {
         processor.start();
 
         System.out.println("Press enter to stop");
-        Scanner scanner = new Scanner(System.in);
-        scanner.nextLine();
+        try (Scanner scanner = new Scanner(System.in)) {
+            scanner.nextLine();
+        }
         processor.shutdown();
     }
 }
 
 class Processor extends Thread {
     private volatile boolean running = true;
+
     @Override
     public void run() {
         while (running) {
             System.out.println("From thread " + Thread.currentThread().getName());
             try {
                 Thread.sleep(1000);
-            } catch (Exception e) {}
+            } catch (Exception e) {
+            }
         }
     }
 

multithreading/src/main/java/com/rakeshv/demo3/Worker.java

@@ -1,6 +1,5 @@
 package com.rakeshv.demo3;
 
-import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 
@@ -29,7 +28,8 @@ public void run() {
 
         try {
             Thread.sleep(3000);
-        } catch (Exception e) {}
+        } catch (Exception e) {
+        }
         System.out.println("Ending count is " + count);
     }
 }

multithreading/src/main/java/com/rakeshv/locks/ConditionsDemo.java

@@ -9,6 +9,7 @@
 
 public class ConditionsDemo {
     InnerStack stack;
+
     public static void main(String[] args) {
         InnerStack stack = new InnerStack();
         Producer producer = new Producer(stack);
@@ -26,6 +27,7 @@ static class InnerStack {
         private Condition stackFullCondition;
         private Condition stackEmptyCondition;
         private boolean hasMoreItems;
+
         InnerStack() {
             stack = new Stack<Object>();
             lock = new ReentrantLock();
@@ -45,7 +47,7 @@ void push(Object o) {
                 Thread.sleep(1000);
                 stackEmptyCondition.signal();
             } catch (Exception e) {
-                //TODO: handle exception
+                e.printStackTrace();
             } finally {
                 lock.unlock();
             }
@@ -61,7 +63,7 @@ void pop() {
                 Thread.sleep(1000);
                 stackFullCondition.signal();
             } catch (Exception e) {
-                //TODO: handle exception
+                e.printStackTrace();
             } finally {
                 lock.unlock();
             }
@@ -71,7 +73,7 @@ void pop() {
     static class Producer {
         private InnerStack stack;
         ExecutorService executor;
-        
+
         Producer(InnerStack stack) {
             this.stack = stack;
             executor = Executors.newSingleThreadExecutor();
@@ -97,7 +99,7 @@ private void produce() {
     static class Consumer {
         private InnerStack stack;
         ExecutorService executor;
-        
+
         Consumer(InnerStack stack) {
             this.stack = stack;
             executor = Executors.newSingleThreadExecutor();

multithreading/src/main/java/com/rakeshv/locks/ReentrantLocks.java

@@ -7,6 +7,7 @@
 public class ReentrantLocks {
     int value = 0;
     ReentrantLock lock = new ReentrantLock();
+
     public static void main(String[] args) {
         ExecutorService executor = Executors.newFixedThreadPool(3);
         ReentrantLocks locks = new ReentrantLocks();
@@ -26,7 +27,6 @@ public void increment() {
             System.out.println("Count is " + value);
             Thread.sleep(1000);
         } catch (InterruptedException e) {
-            // TODO Auto-generated catch block
             e.printStackTrace();
         } finally {
             lock.unlock();

multithreading/src/main/java/com/rakeshv/mythreads/App.java

@@ -7,17 +7,16 @@
 
 public class App {
     public static void main(String[] args) {
-        Count count = new Count();
 
         for (var i = 0; i < 10; i++) {
-                Thread thread = new Thread(() -> {
-                    try {
-                        Count.increment();
-                    } catch (InterruptedException e) {
-                        e.printStackTrace();
-                    }
-                });
-                thread.start();
+            Thread thread = new Thread(() -> {
+                try {
+                    Count.increment();
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                }
+            });
+            thread.start();
         }
     }
 
@@ -48,9 +47,9 @@ public static void increment() throws InterruptedException {
         if (lock.tryLock(1000, TimeUnit.MILLISECONDS)) {
             try {
                 int current = counter;
-                System.out.println("Before: " + current + " thread id " + Thread.currentThread().getId());
+                System.out.println("Before: " + current + " thread id " + Thread.currentThread().threadId());
                 counter = current + 1;
-                System.out.println("After: " + counter + " thread id " + Thread.currentThread().getId());
+                System.out.println("After: " + counter + " thread id " + Thread.currentThread().threadId());
             } finally {
                 lock.unlock();
             }