update

oj/concurrent/TestCallable.java

@@ -0,0 +1,23 @@
+import java.util.concurrent.*;
+
+public class TestCallable {
+    public static void main(String[] args) throws Exception {
+        MyCallable callable = new MyCallable();
+        FutureTask<String> future = new FutureTask<>(callable);
+        Thread thread = new Thread(future);
+        thread.start();
+        System.out.println(future.get());
+    }
+}
+
+class MyCallable implements Callable<String> {
+    @Override
+    public String call() {
+        try {
+            Thread.sleep(1000);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+        return "Finished.";
+    }
+}

oj/concurrent/TestRunnable.java

@@ -0,0 +1,19 @@
+public class TestRunnable {
+    public static void main(String[] args) {
+        MyRunnable runnable = new MyRunnable();
+        Thread thread = new Thread(runnable);
+        thread.start();
+    }
+}
+
+class MyRunnable implements Runnable {
+    @Override
+    public void run() {
+        try {
+            Thread.sleep(1000);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+        System.out.println("Finished.");
+    }
+}

oj/oo-design/classloader/Main.java

@@ -0,0 +1,9 @@
+package sun.applet;
+
+public class Main {
+    public Main() {}
+
+    public static void main(String[] args) {
+        System.out.println("Test class loader.");
+    }
+}