原理：

时序图：

 

 代码清单：

Printable

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

PrintProxy

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

Printer

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

Main

public class Main {    public static void main(String[] args){        Printable p = new PrinterProxy("A1");        System.out.println("现在的名字:"+p.getPrinterName());        p.setPrinterName("B1");        System.out.println("现在的名字:"+p.getPrinterName());        p.print("你好");    }}