What is the difference between "architecture-neutral" and "portable"?

Question

I'm reading Herbert Schildt's book "Java: The Complete Reference" and there he writes that Java is portable AND architecture-neutral. What is the difference between this two concepts? I couldn't understand it from the text.

Answer 1

Take a look at this white paper on Java.

Basically they're saying that in addition to running on multiple environments (because of being interpreted within the JVM), it also runs the same regardless of environment. The former is what makes it portable, the latter is what makes it architecture-neutral. For example, the size of an int does not vary based on platform; it's established by the JVM.

Answer 2

A portable C program:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    printf("Hello, World!");

    return (EXIT_SUCCESS);
}

You can take that C program and compile it on any machine with a C compiler and have it work (assuming it supports printf... I am guessing some things out there may not).

If you compile it on Windows and try to run that binary on a Mac it won't work.

The same sort of program written in Java will also compile on any machine with a Java compiler installed, but the resulting .class file will also run on any machine with a Java VM. That is the architectural neutral part.

So, portable is a source code idea, while architectural neutral is an executable idea.

Answer 3

Looking around I found another book that describes the difference between the two.

For architecture neutral the compiler will generate an architecture-neutral object file meaning that compiled Java code (bytecode) can run on many processors given the presence of a Java runtime.

For portable it means there are are no implementation-dependent aspects of the specification. For instance in C++ an int can be 16-bit, or 32 bit depending on who is implementing the specification where as in Java an int is always 32 bit.

I got my information from a different book (Core Java 2: Fundamentals) so it may differ from his meaning. Here is a link: Core Java 2: Fundamentals

Answer 4

With architecture-neutral, the book means that the byte code is independent of the underlying platform that the program is running on. For example, it doesn't matter if your operating system is 32-bit or 64-bit, the Java byte code is exactly the same. You don't have to recompile your Java source code for 32-bit or 64-bit. (So, "architecture" refers to the CPU architecture).

"Portable" means that a program written to run on one operating system works on another operating system without changing anything. With Java, you don't even have to recompile the source code; a *.class file compiled on Windows, for example, works on Linux, Mac OS X or any other OS for which you have a Java virtual machine available.

Note that you have to take care with some things to make your Java code truly portable. If you for example hard-code Windows-style file paths (C:\Users\Myself...) in your Java application, it is not going to work on other operating systems.