由JAVA参数传递引发的对引用的思考

今天在编写一个快速排序函数，其中想用一个在C++中类似swap功能的函数，结果引发了一系列的问题。
下面是在网上搜到的代码，并在我的本地机上作了运行。   
    
  public   class   ParamTest  
  {  
  public   static   void   main(String[]   args)  
  {  
  /*  
    *Test   1:Methods   can't   modify   numeric   parameters  
  */  
  System.out.println("Testing   tripleValue:");  
  double   percent   =   10;  
  System.out.println("Before:   percent   ="   +   percent);  
  tripleValue(percent);  
  System.out.println("After:   percent   =   "   +   percent);  
   
  /*  
    *Test   2:   Methods   can   change   the   state   of   object    
    * parameters  
  */  
  System.out.println("\nTesting   tripleSalary:");  
  Employee   harry   =   new   Employee("Harry",50000);  
  System.out.println("Before:   salary   ="   +   harry.getSalary());  
  tripleSalary(harry);  
  System.out.println("After:   salary   ="   +   harry.getSalary());  
   
  /*  
    *Test   3:   Methods   can't   attach   new   objects   to    
    * object   parameters  
  */  
  System.out.println("\nTesting   swap:");  
  Employee   a   =   new   Employee("Alice",70000);  
  Employee   b   =   new   Employee("Bob",60000);  
  System.out.println("Before:   a &nb