Java

References

• Good cheat sheet: https://introcs.cs.princeton.edu/java/11cheatsheet/

• Java Sandbox: https://repl.it/languages/java

• Tutorials

  • Oracle Java Documentation: https://docs.oracle.com/javase/tutorial/tutorialLearningPaths.html

    • Language basics

      • https://docs.oracle.com/javase/tutorial/java/index.html
      • https://docs.oracle.com/javase/tutorial/java/nutsandbolts/index.html

    • Classes and Objects: https://docs.oracle.com/javase/tutorial/java/javaOO/index.html

    • Interfaces and Inheritance: https://docs.oracle.com/javase/tutorial/java/IandI/index.html

    • Concurrency: https://docs.oracle.com/javase/tutorial/essential/concurrency/index.html

  • https://www.w3schools.com/java/

  • https://www.javatpoint.com/java-tutorial

  • Interactive Tutorials: https://www.learnjavaonline.org/

  • Packaging Programs in JARs: https://docs.oracle.com/javase/tutorial/deployment/jar/index.html

  • Baeldung “Back to Basics”: https://www.baeldung.com/java-tutorial

Solutions

ThreadPoolExecutor

Good Example: https://www.journaldev.com/1069/threadpoolexecutor-java-thread-pool-example-executorservice

Pass a List <objects that implement an interface> to a Method

https://stackoverflow.com/questions/10090167/how-can-you-pass-a-listobjects-that-implement-an-interface-to-a-method

Use: List<? extends YourInterface>

public Interface JsonEnabled {
    public String getAsJson();
}

public class User implements JsonEnabled {
    ....
    @Override
    public String getAsJson() {...}
}

public class TheServlet {
    ...
    private String getUserListAsJson() {
        List<User> userList = this.dao.getUsers();
        return this.getListAsJson(userList);
    }

    private String getListAsJson(List<? extends JsonEnabled> list) { ... }
        // The loop code that is in each method.
    }
}

Thread Sleep

Example of passing “……” to indicate wait times: https://www.rabbitmq.com/tutorials/tutorial-two-java.html

private static void doWork(String task) throws InterruptedException {
    for (char ch: task.toCharArray()) {
        if (ch == '.') Thread.sleep(1000);
    }
}