单例类

 public class Singleton
{
 private static Singleton obj = null;
 public static Singleton getInstance()
 {
  if(null == obj)
  {
   obj = new Singleton();
  }
  return obj;
 }
 
 public static void main(String[] args)
 {
  Singleton obj1 = Singleton.getInstance();
  Singleton obj2 = Singleton.getInstance();
  System.out.println(obj1 == obj2);
 }
}