java-patterns.java

package ro.inf.prg2.uebung06.loesung;

import java.io.OutputStream;
import java.io.PrintStream;
import java.util.*;

/**
 * =======================================================
 * Singleton Pattern & Testing
 * =======================================================
 */

public class Logger {
    private static Logger instance = new Logger(System.out);
    private PrintStream ps;

    private Logger(PrintStream ps) {
        this.ps = ps;
    }

    public static Logger getInstance() {
        return instance;
    }

    public void setPs(PrintStream ps) {
        this.ps = ps;
    }

    public void log(String message) {
        ps.println(message);
    }
}

class MockPrintStream extends PrintStream {

    private String buffer;

    public MockPrintStream(OutputStream out) {
        super(out);
    }

    public String getBuffer() {
        return buffer;
    }

    @Override
    public void println(String x) {
        buffer = x;
    }
}

/**
 * =======================================================
 * Observer Pattern
 * =======================================================
 */

class View extends Observable implements Observer {
    private String htmlContent = "";
    private List<Observer> observables;

    public View() {
        this.observables = new ArrayList<>();
    }

    public String getHtmlContent() {
        return htmlContent;
    }

    public void setHtmlContent(String htmlContent) {
        this.htmlContent = htmlContent;
    }

    @Override
    public void update(Observable o, Object arg) {
        htmlContent = (String) arg;
    }

    @Override
    public synchronized void addObserver(Observer o) {
        observables.add(o);
    }

    @Override
    public void notifyObservers() {
        observables.forEach(observer -> observer.update(this, htmlContent));
    }

    public void postData(String data) {
        htmlContent += data;
    }
}

/**
 * Modern MVC as described here: https://developer.chrome.com/static/images/mvc.png
 *
 * Controller communicates between Model and View. Model and View don't know each other.
 */
class Controller implements Observer {
    private View view;
    private Model model;

    public Controller(View view, Model model) {
        this.view = view;
        view.addObserver(this);

        this.model = model;
        model.addObserver(this);
    }

    @Override
    public void update(Observable o, Object arg) {
        if (o instanceof View) {
            model.addData((String) arg);
        } else {
            view.postData((String) arg);
        }
    }
}

class Model extends Observable implements Observer {
    private List<String> users;
    private List<Observer> observables;

    public List<String> getUsers() {
        return users;
    }

    public void setUsers(List<String> users) {
        this.users = users;
    }

    public Model() {
        this.users = new ArrayList<>();
        this.observables = new ArrayList<>();
    }

    @Override
    public synchronized void addObserver(Observer o) {
        observables.add(o);
    }

    @Override
    public void update(Observable o, Object arg) {
        users.add((String) arg);
    }

    @Override
    public void notifyObservers() {
        observables.forEach(observer -> observer.update(this, users.isEmpty() ? "" : users.get(users.size() - 1)));
    }

    public void addData(String data) {
        users.add(data);
    }
}

/**
 * =======================================================
 * Composite Pattern
 * =======================================================
 */

abstract class Employee {
    private String name;
    private String department;

    public Employee(String name, String department) {
        this.name = name;
        this.department = department;
    }

    public String getName() {
        return name;
    }

    public String getDepartment() {
        return department;
    }
}

class Worker extends Employee {
    public Worker(String name, String department) {
        super(name, department);
    }
}

class Boss extends Employee {

    private String management;
    private List<Employee> employees;

    public Boss(String name, String department, String management) {
        super(name, department);
        this.management = management;
        employees = new ArrayList<>();
    }

    public String getManagement() {
        return management;
    }

    public void addEmployee(Employee employee) {
        if (getManagement().equals(employee.getDepartment())) {
            employees.add(employee);
            return;
        }

        employees.forEach(employee1 -> {
            if (employee1 instanceof Boss) {
                ((Boss) employee1).addEmployee(employee);
            }
        });
    }

    public int employeeCount() {
        int count = 0;
        for (Employee employee : employees) {
            if (employee instanceof Worker) {
                count += 1;
            } else {
                count += 1 + ((Boss) employee).employeeCount();
            }
        }
        return count;
    }
}

class Company {
    private Boss ceo;

    public Company() {
        this.ceo = new Boss("Huettl", "FH", "FH");
    }

    public void addEmployee(Employee employee) {
        ceo.addEmployee(employee);
    }

    public int employeeCount() {
        return ceo.employeeCount();
    }
}

/**
 * =======================================================
 * Tests
 * =======================================================
 */

class Test {
    public static void main(String... args) {
        System.out.println("\nLogger");
        testLogger();

        System.out.println("\nComposite");
        testComposite();

        System.out.println("\nObserver");
        testObserver();
    }

    private static void testObserver() {
        Model model = new Model();
        View view = new View();
        Controller controller = new Controller(view, model);
        model.addData("Test");
        model.notifyObservers();
        if (view.getHtmlContent().equals("Test")) {
            System.out.println("Success");
        } else {
            System.out.println("Failure");
        }

        view.postData("TestView");
        view.notifyObservers();
        if (model.getUsers().size() == 2) {
            System.out.println("Success");
        } else {
            System.out.println("Failure");
        }
    }

    private static void testComposite() {
        Company company = new Company();
        company.addEmployee(new Boss("Beneken", "FH", "IT"));
            company.addEmployee(new Worker("Original Michi", "IT"));
            company.addEmployee(new Worker("Michi 1", "IT"));
            company.addEmployee(new Boss("Slave Master", "IT", "SE2"));
                company.addEmployee(new Worker("Praktikant 1", "SE2"));
                company.addEmployee(new Worker("Praktikant 2", "SE2"));
        if (company.employeeCount() == 6) {
            System.out.println("Success");
        } else {
            System.out.println("Failure");
        }
    }

    private static void testLogger() {
        Logger logger = Logger.getInstance();
        final MockPrintStream mockPrintStream = new MockPrintStream(System.out);

        logger.setPs(mockPrintStream);
        logger.log("test");
        if (Objects.equals(mockPrintStream.getBuffer(), "test")) {
            System.out.println("Success");
        } else {
            System.out.println("Failure");
        }
    }
}