我喜欢的两种单例写法

 1 package ToolPackage
 2 {
 3  /**
 4   * 提示
 5   * @author tqr <br />
 6   * 创建时间：2014-11-7 下午6:27:10
 7   */
 8  public class Tip
 9  {
10   private static  var instanceB:Boolean=true;  
11   private static var instance:Tip;
12   
13   public function Tip()
14   {
15    if (instanceB) {  
16     throw new Error("该类为单例，只能用getInstance()来获取实例");  
17    }  
18   }
19   
20   public static function getInstance():Tip{
21    if (!instance) {  
22     instanceB = false;  
23     instance = new Tip();  
24     instanceB = true;  
25    }  
26    return instance;  
27   }
28   
29  }
30 }

 1 package ToolPackage
 2 {
 3  /**
 4   * 提示
 5   * @author tqr <br />
 6   * 创建时间：2014-11-7 下午6:27:10
 7   */
 8  public class Tip
 9  {
10   private static var instance:Tip = new Tip();
11   
12   public function Tip()
13   {
14    if (instance) {  
15     throw new Error("该类为单例，只能用getInstance()来获取实例");  
16    }  
17   }
18   
19   public static function getInstance():Tip{
20    return instance;  
21   }
22   
23  }
24 }