printer.java

一个经典的单例模式demo（模拟打印机）

package single;

import java.io.InputStream;

public class Printer {
	private static Printer pt;
	
	public static Printer getPt(){
		if(pt!=null){
			return pt;
		}else{
			makept();
			return pt;
		}
	}
	
	public static synchronized void makept(){
		if(pt==null){
			pt=new Printer();
		}
	}
	public void print(){
		System.out.println("is printing....");
	}
}