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You're welcome ...

About why Java is still used I think there are two main reasons:

1. There's IMO no other runtime which is implemented on such a wide spreaded hardware devices (beside computers with Linux, Windows, OSx it even runs on things like routers, smartphones, MP3 players, watches, in cars, lot's of more), there's nearly nothing which is any kind of computer where no JVM exists for so it's one of the most real platform independant languages.

2. It's an easy and clear designed OO language for beginners to learn object orientated programming without need to fight with C++ stuff like pointers, memory allocation, build chains (compiling and linking), maybe more, so it's often used for educational reasons.

To be honest I for myself don't really like Java allthough I know it's powerful and even has some neat features which aren't possible in C++ (because Java instead is some kind of mixed compiled and interpreted) I more like to work with C++ which nearly doesn't have any restrictions (i.e. I hate it lot's of Java classes are 'final' so it's not possible to derive from them).

But this is just my opinion ...

Best regards,

ZOPPO

Thanks for your detailed reply.

Last Optional question or advice.
I am doing  a lot, php, javascipt(jquery)  programming, but those are interpreted language for web browser. If we are going to develope some web application, I think node.js and javascript ,php is good enough . Java runtime installed on client server or user PC  can be replaced by node.js which is written in C++ and also browser javascript engine is also written in C++ such as chrome V8 engine  , so I don't know why Java programming is still existing if you can be familar with C, C++,C# with php, javascript, node.js, jquery, HTML5  and those code is  open source  ? the reason of java is still being used that I think it is history for java, a lot application is based on java  with its commercial proprietary.

So I guess I am going to go back or spend more time on C, C++ and C#  from tutorial and give up  java  programming which its source is NOT open  source to public. For example, you can find  a lot of most updated open source HTML5 javascript Game code but for java Game code is really outdated you can find on internet.

Please advise

as I know inline as CSS style on tag such as <a style='font-size'></a> that is inline style which is not from CSS file

Zoppo,  what you mean, "inline" for C++?

Question-1

I am asking

      /* Method-1 */
        Circle(double r) //parameterized constructor
        {radius = r;}
            /* Method-2
            Circle :: Circle(double r){radius = r; }
            */

Is method -1 no different from Mehtod-2 ?

Question-2,
Your answer is  no difference, besides compiler time, why programmer prefer to declare it externally? It seems it can be controlled easily, somehow in programming since the class may not in the same main file or they are in header file.

Please advise


Rwniceing

Additional info about copy-constructor - as told it's called in two cases:

  Circle c;

  Circle c1( c ); // first case
  Circle c2 = c; // second case

There's a third case which looks quite similare to the second one:

   Circle c3;
   c3 = c;

That's a bit suprising because in this case the copy constructor is not called, instead the default constructor is called in the first line, in the second one a (maybe implicit generated) assignment operator is called.

From my experience it is a good practice to implement it somehow like this:

  class Circle
  {
   ...
    Circle& operator = ( const Circle& src ) // assignment operator
    {
      m_radius = src.m_radius;
      return *this;
    }
    Circle( const Circle& src ) { *this = src; } // copy constructor
  };

This has the advantages that all of the above shown cases call the same assignment operator and, i.e. if a new member is added it doesn't need to be handled twice in the copy constructor and the assignment operator.

ZOPPO

Hi rwniceing,

about 1.: the comments already describe the kind of constructors:
- Circle() is a default contrustor which is needed to initialize default values some simple call like
     Circle c;
- Circle( double r ) is a specialized constructor which implements a convenient way to initialize values.
  For example it's easier/nicer to write
     Circle c(1.5);
  instead of
     Circle c;
     c.setRadius( 1.5 );
- Circle(Circle &t) is a copy constructor which copies values from a given instance to the new created one whenever one of these calls are used:
     Circle c1( c );
     Circle c2 = c;
 
about 2.: There's no (real) difference between implementing a function within a class where it's declared or to declare it in the class and implement it outside, i.e.:

  class X
  {
   void foo() { /*do something*/ } // declared and implemented at one place
   void bar(); // declared here, implemented outsied
  }

  void X::bar() // implementation
  { /*do something*/ }

It's common to implement (at least larger) functions outside of the class declaration to keep that declaration small. It's even very common to move the implementation out of the header i.e. into a .cpp because it saves compile time (exceptions are inline functions and templates, they need to be implemented within the file where they're declared).

about 3.: Whenever you need to 'tell' the compiler something (like i.e. a function or a static variable) belongs to a class which is declared elsewhere you need to prefix it with the class name scope (in your example the 'Circle::').

This is because it maybe another class even declares and implements a function 'Circle' so the compiler wouldn't know which function belongs to which class.

Hope that helps,

ZOPPO