libs-base/Documentation/manual/ObjcAndJavaC++.texi

@node Objective-C Java and C++
@appendix Differences and Similarities Between Objective-C, Java, and C++
@cindex Objective-C and Java, differences and similarities
@cindex differences and similarities, Objective-C and Java
@cindex Objective-C and C++, differences and similarities
@cindex differences and similarities, Objective-C and C++

@paragraphindent 0

This appendix explains the differences/similarities between Objective-C and
Java. It does not cover the Java Interface to GNUstep (JIGS; see @ref{Java and
Guile}), but is included to help people who want to learn Objective-C and know
Java already.


@section General

@itemize @bullet

@item
C programmers may learn Objective-C in hours (though real expertise
obviously takes much longer).

@item
Java has global market acceptance.

@item
Objective-C is a compiled OO programming language.

@item
Java is both compiled and interpreted and therefore does not offer
the same run-time performance as Objective-C.

@item
Objective-C features efficient, transparent Distributed Objects.

@item
Java features a less efficient and less transparent Remote Machine
Interface.

@item
Objective-C has basic CORBA compatibility through official C bindings,
and full compatibility through unofficial Objective-C bindings.

@item
Java has CORBA compatibility through official Java bindings.

@item
Objective-C is portable across heterogeneous networks by virtue of a
near omnipresent compiler (gcc).

@item
Java is portable across heterogeneous networks by using client-side JVMs
that are software processors or runtime environments.

@end itemize


@section Language

@itemize @bullet

@item
Objective-C is a superset of the C programming language, and may
be used to develop non-OO and OO programs. Objective-C provides
access to scalar types, structures and to unions, whereas Java
only addresses a small number of scalar types and everything else
is an object.  Objective-C provides zero-cost access to existing
software libraries written in C, Java requires interfaces to be
written and incurs runtime overheads.

@item
Objective-C is dynamically typed but also provides static typing.
Java is statically typed, but provides type-casting mechanisms to
work around some of the limitations of static typing.

@item
Java tools support a convention of a universal and distributed
name-space for classes, where classes may be downloaded from
remote systems to clients. Objective-C has no such conventions
or tool support in place. 

@item
Using Java, class definitions may not be extended or divided through
the addition of logical groupings.  Objective-C provides categories
as a solution to this problem.

@item
Objective-C provides delegation (the benefits of multiple inheritance
without the drawbacks) at minimal programming cost.  Java requires
purpose written methods for any delegation implemented.

@item
Java provides garbage collection for memory management.  Objective-C
provides manual memory management, reference counting, and garbage
collection as options.

@item
Java provides interfaces, Objective-C provides protocols.

@end itemize


@section Source Differences

@itemize @bullet
@item
Objective-C is based on C, and the OO extensions are comparable with
those of Smalltalk. The Java syntax is based on the C++ programming
language. 

@item
The object (and runtime) models are comparable, with Java's
implementation having a subset of the functionality of that
of Objective-C.

@end itemize


@section Compiler Differences
 
@itemize @bullet

@item
Objective-C compilation is specific to the target system/environment,
and because it is an authentic compiled language it runs at higher
speeds than Java.

@item
Java is compiled into a byte stream or Java tokens that are interpreted
by the target system, though fully compiled Java is possible.

@end itemize


@section Developer's Workbench

@itemize @bullet

@item
Objective-C is supported by tools such as GNUstep that provides
GUI development, compilation, testing features,
debugging capabilities, project management and database access.
It also has numerous tools for developing projects of different
types including documentation.

@item
Java is supported by numerous integrated development environments
(IDEs) that often have their origins in C++ tools.
Java has a documentation tool that parses source code and creates
documentation based on program comments. There are similar features
for Objective-C.

@item
Java is more widely used.

@item
Objective-C may leverage investment already made in C based tools.

@end itemize


@section Longevity

@itemize @bullet

@item
Objective-C has been used for over ten years, and is considered to be
in a stable and proven state, with minor enhancements from time to time.

@item
Java is evolving constantly.

@end itemize


@section Databases

@itemize @bullet
@item
Apple's EOF tools enable Objective-C developers to build object
models from existing relational database tables. Changes in the
database are automatically recognised, and there is no requirement
for SQL development.

@item
Java uses JDBC that requires SQL development; database changes
affect the Java code. This is considered inferior to EOF. Enterprise
JavaBeans with container managed persistence provides a limited database
capability, however this comes with much additional baggage.  Other
object-relational tools and APIs are being developed for Java (ca. 2004), but
it is unclear which of these, if any, will become a standard.

@end itemize


@section Memory

@itemize @bullet

@item
For object allocation Java has a fixed heap whose maximum size
is set when the JVM starts and cannot be resized unless the
JVM is restarted. This is considered to be a disadvantage in
certain scenarios: for example, data read from databases may
cause the JVM to run out of memory and to crash.

@item
Objective-C's heap is managed by the OS and the runtime system.
This can typically grow to consume all system memory (unless
per-process limits have been registered with the OS).

@end itemize


@section Class Libraries
@itemize @bullet

@item
Objective-C: Consistent APIs are defined by the OpenStep specification.
This is implemented by GNUstep and Mac OS X Cocoa.  Third-party APIs are
available (called Frameworks).

@item
Java: APIs are defined and implemented by the Sun Java Development
Kit distributions.  Other providers of Java implementations (IBM, BEA, etc.)
implement these as well.

@item
The Java APIs are complex owing to the presence of multiple layers of
evolution while maintaining backwards compatibility.  Collections, IO, and
Windowing are all examples of replicated functionality, in which the copies
are incompletely separated, requiring knowledge of both to use.

@item
The OpenStep API is the result of continuing evolution but backward
compatibility was maintained by the presence of separate library versions.
Therefore the API is clean and nonredundant.  Style is consistent.

@item
The OpenStep non-graphical API consists of about 70 classes and about 150
functions.

@item
The equivalent part of the Java non-graphical API consists of about 230
classes.

@item
The OpenStep graphical API consists of about 120 classes and 30 functions.

@item
The equivalent part of the Java graphical API consists of about 450 classes.

@end itemize