BAEL-1327 Java Threads: notify and wait (initial commit) (#3160)

core-java-concurrency/src/main/java/com/baeldung/concurrent/waitandnotify/Data.java

@@ -0,0 +1,33 @@
+package com.baeldung.concurrent.waitandnotify;
+
+public class Data {
+    private String packet;
+    
+    // True if receiver should wait
+    // False if sender should wait
+    private boolean transfer = true;
+ 
+    public synchronized String receive() {
+        while (transfer) {
+            try {
+                wait();
+            } catch (InterruptedException e) {}
+        }
+        transfer = true;
+
+        notifyAll();
+        return packet;
+    }
+ 
+    public synchronized void send(String packet) {
+        while (!transfer) {
+            try { 
+                wait();
+            } catch (InterruptedException e) {}
+        }
+        transfer = false;
+        
+        this.packet = packet;
+        notifyAll();
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/waitandnotify/NetworkDriver.java

@@ -0,0 +1,12 @@
+package com.baeldung.concurrent.waitandnotify;
+
+public class NetworkDriver {
+    public static void main(String[] args) {
+        Data data = new Data();
+        Thread sender = new Thread(new Sender(data));
+        Thread receiver = new Thread(new Receiver(data));
+        
+        sender.start();
+        receiver.start();
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/waitandnotify/Receiver.java

@@ -0,0 +1,25 @@
+package com.baeldung.concurrent.waitandnotify;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+public class Receiver implements Runnable {
+    private Data load;
+ 
+    public Receiver(Data load) {
+        this.load = load;
+    }
+ 
+    public void run() {
+        for(String receivedMessage = load.receive();
+          !"End".equals(receivedMessage) ;
+          receivedMessage = load.receive()) {
+            
+            System.out.println(receivedMessage);
+
+            //Thread.sleep() to mimic heavy server-side processing
+            try {
+                Thread.sleep(ThreadLocalRandom.current().nextInt(1000, 5000));
+            } catch (InterruptedException e) {}
+        }
+    }
+}

core-java-concurrency/src/main/java/com/baeldung/concurrent/waitandnotify/Sender.java

@@ -0,0 +1,30 @@
+package com.baeldung.concurrent.waitandnotify;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+public class Sender implements Runnable {
+    private Data data;
+ 
+    public Sender(Data data) {
+        this.data = data;
+    }
+ 
+    public void run() {
+        String packets[] = {
+            "First packet",
+            "Second packet",
+            "Third packet",
+            "Fourth packet",
+            "End"
+        };
+ 
+        for (String packet : packets) {
+            data.send(packet);
+            
+            //Thread.sleep() to mimic heavy server-side processing
+            try {
+                Thread.sleep(ThreadLocalRandom.current().nextInt(1000, 5000));
+            } catch (InterruptedException e) {}
+        }
+    }
+}

core-java-concurrency/src/test/java/com/baeldung/concurrent/waitandnotify/NetworkIntegrationTest.java

@@ -0,0 +1,65 @@
+package com.baeldung.concurrent.waitandnotify;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.io.PrintWriter;
+import java.io.StringWriter;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+public class NetworkIntegrationTest {
+
+	private final ByteArrayOutputStream outContent = new ByteArrayOutputStream();
+	private final ByteArrayOutputStream errContent = new ByteArrayOutputStream();
+	private String expected;
+	
+	@Before
+	public void setUpStreams() {
+	    System.setOut(new PrintStream(outContent));
+	    System.setErr(new PrintStream(errContent));
+	}
+	
+	@Before
+	public void setUpExpectedOutput() {
+		StringWriter expectedStringWriter = new StringWriter();
+		
+		PrintWriter printWriter = new PrintWriter(expectedStringWriter);
+		printWriter.println("First packet");
+		printWriter.println("Second packet");
+		printWriter.println("Third packet");
+		printWriter.println("Fourth packet");
+		printWriter.close();
+		
+		expected = expectedStringWriter.toString();
+	}
+
+	@After
+	public void cleanUpStreams() {
+	    System.setOut(null);
+	    System.setErr(null);
+	}
+	
+	@Test
+	public void givenSenderAndReceiver_whenSendingPackets_thenNetworkSynchronized() {
+        Data data = new Data();
+        Thread sender = new Thread(new Sender(data));
+        Thread receiver = new Thread(new Receiver(data));
+        
+        sender.start();
+        receiver.start();
+        
+        //wait for sender and receiver to finish before we test against expected
+        try {
+			sender.join();
+			receiver.join();
+		} catch (InterruptedException e) {
+			e.printStackTrace();
+		}
+		
+	    assertEquals(expected, outContent.toString());
+	}
+}