🔒 Java 로 동기화를 해보자!

public class Computer {

    public static void main(String[] args) {
        final WebBrowser webBrowser = new WebBrowser(5);

        final Thread threadA = new Thread(new WebSite("Google", webBrowser));
        final Thread threadB = new Thread(new WebSite("Naver", webBrowser));
        final Thread threadC = new Thread(new WebSite("Daum", webBrowser));

        threadA.start();
        threadB.start();
        threadC.start();
    }
}

public class WebSite implements Runnable {

    private final String webSiteName;
    private final WebBrowser webBrowser;

    public WebSite(final String webSiteName, final WebBrowser webBrowser) {
        this.webSiteName = webSiteName;
        this.webBrowser = webBrowser;
    }

    @Override
    public void run() {
        // 메서드 블럭 동기화
        synchronized (this) {
            while (webBrowser.hasSpace()) {
                try {
                    Thread.sleep(new Random().nextInt(1000));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                webBrowser.createNewTab(webSiteName);
            }
        }
    }
}

public class WebBrowser {

    private static final String SPACE = " ";
  
    private final List<String> webSiteNames = new ArrayList<>();
    private final int maxWebCount;

    public WebBrowser(final int maxWebCount) {
        this.maxWebCount = maxWebCount;
    }

    // 메서드 동기화
    public synchronized void createNewTab(final String webSiteName) {
        try {
            if (full()) {
                return;
            }
            System.out.println(webSiteName + " 사이트가 켜지는 중입니다...");
            Thread.sleep(new Random().nextInt(1000));
            webSiteNames.add(webSiteName);
            showRunningBrowser();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private void showRunningBrowser() {
        if (webSiteNames.size() > maxWebCount) {
            throw new UnsupportedOperationException("현재 브라우저 탭이 6개 이상 활성화 되어 강제 종료합니다...");
        }

        System.out.println("┌───────────────────────────────────────────────────────────────────────────────┐");
        System.out.println("│ ◆ Wilder Web Browser                                                    - □ x │");
        System.out.println("└───────────────────────────────────────────────────────────────────────────────┘");

        StringBuilder browserNameLine = new StringBuilder();
        StringBuilder browserUnderLine = new StringBuilder();

        if (webSiteNames.size() > 0) {
            browserNameLine.append("│");
            browserUnderLine.append("└");
        }

        for (int i = 0; i < webSiteNames.size(); i++) {
            browserNameLine.append(generateWebSiteName(webSiteNames.get(i)))
                .append(i + 1)
                .append("   │");
            browserUnderLine.append("───────────────┘");
        }

        System.out.println(browserNameLine);
        System.out.println(browserUnderLine);
    }

    private String generateWebSiteName(final String name) {
        StringBuilder builder = new StringBuilder();

        if (name.length() > 11) {
            return name.substring(0, 11);
        }

        int space = 11 - name.length();
        int interval = space / 2;

        builder.append(SPACE.repeat(interval))
            .append(name)
            .append(SPACE.repeat(11 - interval - name.length()));

        return builder.toString();
    }

    public boolean hasSpace() {
        return webSiteNames.size() < maxWebCount;
    }

    private boolean full() {
        return !hasSpace();
    }
}

    public void createNewTab(final String webSiteName) {
        try {
            if (full()) {
                return;
            }
            System.out.println(webSiteName + " 사이트가 켜지는 중입니다...");
            Thread.sleep(new Random().nextInt(1000));
            webSiteNames.add(webSiteName);
            showRunningBrowser();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void run() {
        while (webBrowser.hasSpace()) {
            try {
                Thread.sleep(new Random().nextInt(1000));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            webBrowser.createNewTab(webSiteName);
        }
    }

public class Computer {

    public static void main(String[] args) {
        final WebBrowser webBrowser = new WebBrowser(5);

        final Thread threadA = new Thread(new WebSite("Google", webBrowser));
        final Thread threadB = new Thread(new WebSite("Naver", webBrowser));
        final Thread threadC = new Thread(new WebSite("Daum", webBrowser));
        final Thread closer = new Thread(new WebSiteCloser(webBrowser));

        closer.start();
        threadA.start();
        threadB.start();
        threadC.start();
    }
}

public class WebSite implements Runnable {

    private final String webSiteName;
    private final WebBrowser webBrowser;

    public WebSite(final String webSiteName, final WebBrowser webBrowser) {
        this.webSiteName = webSiteName;
        this.webBrowser = webBrowser;
    }

    @Override
    public void run() {
        synchronized (this) {
            while (true) {
                try {
                    Thread.sleep(new Random().nextInt(1000));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                webBrowser.createNewTab(webSiteName);
            }
        }
    }
}

public class WebBrowser {

    private static final String SPACE = " ";

    private final List<String> webSiteNames = new ArrayList<>();
    private final List<Integer> webSiteIndexes = new ArrayList<>();
    private final int maxWebCount;
    private int webSiteIndex = 0;

    public WebBrowser(final int maxWebCount) {
        this.maxWebCount = maxWebCount;
    }

    public synchronized void createNewTab(final String webSiteName) {
        try {
            if (full()) {
                wait();
            }
            System.out.println(webSiteName + " 사이트가 켜지는 중입니다...");
            Thread.sleep(new Random().nextInt(1000));
            webSiteNames.add(webSiteName);
            webSiteIndexes.add(++webSiteIndex);
            showRunningBrowser();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private void showRunningBrowser() {
        if (webSiteNames.size() > maxWebCount) {
            throw new UnsupportedOperationException("현재 브라우저 탭이 6개 이상 활성화 되어 강제 종료합니다...");
        }

        System.out.println("┌───────────────────────────────────────────────────────────────────────────────┐");
        System.out.println("│ ◆ Wilder Web Browser                                                    - □ x │");
        System.out.println("└───────────────────────────────────────────────────────────────────────────────┘");

        StringBuilder browserNameLine = new StringBuilder();
        StringBuilder browserUnderLine = new StringBuilder();

        if (webSiteNames.size() > 0) {
            browserNameLine.append("│");
            browserUnderLine.append("└");
        }

        for (int i = 0; i < webSiteNames.size(); i++) {
            browserNameLine.append(generateWebSiteName(webSiteNames.get(i)))
                .append(generateWebSiteIndex(webSiteIndexes.get(i)))
                .append(" │");
            browserUnderLine.append("───────────────┘");
        }

        System.out.println(browserNameLine);
        System.out.println(browserUnderLine);
    }

    private String generateWebSiteName(final String name) {
        StringBuilder builder = new StringBuilder();

        if (name.length() > 11) {
            return name.substring(0, 11);
        }

        int space = 11 - name.length();
        int interval = space / 2;

        builder.append(SPACE.repeat(interval))
            .append(name)
            .append(SPACE.repeat(11 - interval - name.length()));

        return builder.toString();
    }

    private String generateWebSiteIndex(final int index) {
        if (index < 10) {
            return "00" + index;
        }
        if (index < 100) {
            return "0" + index;
        }
        return "" + index;
    }

    public boolean isNotEmpty() {
        return webSiteNames.size() != 0;
    }

    public boolean hasSpace() {
        return webSiteNames.size() < maxWebCount;
    }

    public boolean full() {
        return !hasSpace();
    }

    public synchronized void removeAndNotify() {
        if (isNotEmpty()) {
            System.out.println(webSiteNames.get(0) + " 사이트가 종료됩니다.");
            webSiteNames.remove(0);
            webSiteIndexes.remove(0);
            showRunningBrowser();
            notify();
        }
    }
}

public class WebSiteCloser implements Runnable {

    private final WebBrowser webBrowser;

    public WebSiteCloser(WebBrowser webBrowser) {
        this.webBrowser = webBrowser;
    }

    @Override
    public void run() {
        try {
            while (true) {
                Thread.sleep(3000);
                webBrowser.removeAndNotify();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}