代理模式【PROXY PATTERN】

public class Main
{
    public static void main(String[] args)
    {
        PrinterProxy p = new PrinterProxy("Alice");
        System.out.println(p.getPrinterName());
        p.setPrinterName("Bob");
        System.out.println(p.getPrinterName());
        p.print("Hello, world.");
    }
}

interface Printable
{
    public abstract void setPrinterName(String name);
    
    public abstract String getPrinterName();
    
    public abstract void print(String string);
}

class Printer implements Printable
{
    private String name;
    
    public Printer()
    {
        heavyJob("Printer");
    }
    
    public Printer(String name)
    {
        this.name = name;
        heavyJob("Printer（）" + name);
    }
    
    public void setPrinterName(String name)
    {
        this.name = name;
    }
    
    public String getPrinterName()
    {
        return name;
    }
    
    public void print(String string)
    {
        System.out.println("=== " + name + " ===");
        System.out.println(string);
    }
    
    private void heavyJob(String msg)
    {
        System.out.println(msg);
        for (int i = 0; i < 5; i++)
        {
            try
            {
                Thread.sleep(1000);
            }
            catch (InterruptedException e)
            {
            }
            System.out.print(".");
        }
    }
}

class PrinterProxy implements Printable
{
    private String name;
    
    private Printer real;
    
    public PrinterProxy()
    {
    }
    
    public PrinterProxy(String name)
    {
        this.name = name;
    }
    
    public synchronized void setPrinterName(String name)
    {
        if (real != null)
        {
            real.setPrinterName(name);
        }
        this.name = name;
    }
    
    public String getPrinterName()
    {
        return name;
    }
    
    public void print(String string)
    {
        realize();
        real.print(string);
    }
    
    private synchronized void realize()
    {
        if (real == null)
        {
            real = new Printer(name);
        }
    }
}