Translate C++ Constructor into Java

Question

I'm working on translating a small package from C++ to Java. I've never really used C++, so some of the syntax is a bit of a mystery. In particular, I'm having difficulty working out what the Java equivalent to this would be:

file: SomeClass.cpp

SomeClass::SomeClass( BitStream* data, const char* const filename ) :
    data( data ), cipher( filename ), iv( new Botan::byte [cipher.BLOCK_SIZE] ),
    ivBitsSet( 0 ), keyMaterialRemaining( 0 ), keyMaterial( new Botan::byte [cipher.BLOCK_SIZE] ) {}

I'm happy with (in Java):

public SomeClass{
  public SomeClass(InputStream data, String filename){

  }
}

but I'm not sure what to do with the stuff after the : in the C++. Are they fields? Optional parameters? Apologies for trivial question, but haven't got far with Google on this...

Nim · Accepted Answer · 2010-10-28 15:11:12Z

9

Everything after ":" is called the member initialization list, in C++ this is one way of initialising the members of this class. For example from your code, "data" is a member of SomeClass, so the equivalent in Java would be a simple assignment in the body of the constructor.

this.data = data;

etc. for all the other members

answered Oct 28, 2010 at 15:11

Nim

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Comments

Thomas Lötzer · Accepted Answer · 2010-10-28 15:12:49Z

Those are field initializer lists. They set the initial values for the fields.

The Java-Version is something like

public SomeClass{
  public SomeClass(InputStream data, String filename){
    //either set the field directly...
    this.data = data;
    //...or call the constructor, depending on the type
    this.cipher = new Cipher(filename);
  }
}

Note that this are not necessarily simple field setters, they may also be calls to the field type's constructor.

Johan Kotlinski · Accepted Answer · 2010-10-28 15:11:44Z

2

cipher(filename) is equivalent to writing cipher = filename;

answered Oct 28, 2010 at 15:11

Johan Kotlinski

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1 Comment

Kate Gregory Over a year ago

Not so. But cipher=filename is as close as Java can get to what cipher(filename) does.

siukurnin · Accepted Answer · 2010-10-28 15:09:37Z

1

This simply is the C++ way to initialize all the class members.

answered Oct 28, 2010 at 15:09

siukurnin

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