Initial commit

.classpath

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>

.gitignore

@@ -0,0 +1,2 @@
+.DS_Store
+/bin

.project

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>ex22-square-queue</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>

src/square/SquareQueue.java

@@ -0,0 +1,98 @@
+package square;
+
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.LinkedBlockingQueue;
+
+/**
+ * Squares integers.
+ */
+class Squarer {
+
+    private final BlockingQueue<Integer> in;
+    private final BlockingQueue<SquareResult> out;
+    // Rep invariant: in, out != null
+
+    /**
+     * Make a squarer that will listen for requests and generate replies.
+     * @param requests queue to receive requests from
+     * @param replies queue to send replies to
+     */
+    public Squarer(BlockingQueue<Integer> requests, BlockingQueue<SquareResult> replies) {
+        this.in = requests;
+        this.out = replies;
+    }
+
+    /**
+     * Start handling squaring requests.
+     */
+    public void start() {
+        new Thread(new Runnable() {
+            public void run() {
+                while (true) {
+                    // TODO: we may want a way to stop the thread
+                    try {
+                        // block until a request arrives
+                        int x = in.take();
+                        // compute the answer and send it back
+                        int y = x * x;
+                        out.put(new SquareResult(x, y));
+                    } catch (InterruptedException ie) {
+                        ie.printStackTrace();
+                    }
+                }
+            }
+        }).start();
+    }
+}
+
+/**
+ * An immutable squaring result message.
+ */
+class SquareResult {
+    private final int input;
+    private final int output;
+
+    /**
+     * Make a new result message.
+     * @param input input number
+     * @param output square of input
+     */
+    public SquareResult(int input, int output) {
+        this.input = input;
+        this.output = output;
+    }
+
+    // TODO: we will want more observers, but for now...
+
+    @Override public String toString() {
+        return input + "^2 = " + output;
+    }
+}
+
+public class SquareQueue {
+
+    /**
+     * Create and use a squarer.
+     * @param args unused
+     */
+    public static void main(String[] args) {
+
+        BlockingQueue<Integer> requests = new LinkedBlockingQueue<>();
+        BlockingQueue<SquareResult> replies = new LinkedBlockingQueue<>();
+
+        Squarer squarer = new Squarer(requests, replies);
+        squarer.start();
+
+        try {
+            // make a request
+            requests.put(42);
+
+            // maybe do something concurrently...
+
+            // read the reply
+            System.out.println(replies.take());
+        } catch (InterruptedException ie) {
+            ie.printStackTrace();
+        }
+    }
+}