jdk 中Runtime之单例模式 学习

这段代码是我从源码中截取的，大家很容易看到currentRuntime是一个静态变量，getRunTime对应的就是getInstacne。
不是说这种方法不好吗？

 1 public class Runtime {
 2 45     private static Runtime currentRuntime = new Runtime();
 3 
 4     
 5 Returns the runtime object associated with the current Java application. Most of the methods of class Runtime are instance methods and must be invoked with respect to the current runtime object.
 6 Returns:
 7 the Runtime object associated with the current Java application.
 8 54 
 9 55     public static Runtime getRuntime() {
10 56         return currentRuntime;
11 57     }
12 
13     

 1 package heelo;
 2 class ExecDemo { 
 3         public static void main(String args[]){ 
 4                 Runtime r = Runtime.getRuntime(); 
 5                 Runtime r1=Runtime.getRuntime();
 6                 if(r1==r)
 7                 {
 8                     System.out.println("他们是相同的");
 9                     
10                 }
11                 Process p = null; 
12                 try{ 
13                         p = r.exec("notepad"); //打卡一个记事本程序。你可以再cmd敲个notepad试试
14                 } catch (Exception e) { 
15                         System.out.println("Error executing notepad."); 
16                 } 
17         } 
18 }