Java for C++ Programmers

1. Java for C++ Programmers Clint Jeffery University of Idaho jeffery@uidaho.edu

2. Object Oriented Programming • Object Oriented Design comes first. • Objects originated in application domains. • OOP first appeared in SIMULA 67 • classes and inheritance mixed w/ normal code • Popularized by SmallTalk 80 • everything is an object, even integers! • Method call == “send an object a message”

3. History of Java • Designed by Gosling et al at Sun ~1991 • Original niche: embedded programming w/ GUIs, such as cable TV boxes • Portability based on bytecode VM • Happy Accident: retargeted for browsers just in time for Internet boom, 1995 • Moves largely onto enterprise servers by 1999 or so • Achieves 50+% university penetration, ~2005 • Returns to its roots in Android, ~2008

4. Java Design Principles • Simple, object-oriented, familiar • Robust and secure • Architecture neutral and portable • Interpreted, threaded, and dynamic • High performance (?)

5. Java as a Better C++ • Familiar == C/C++-like syntax • Tries to avoid main sources of bugs and security flaws in C++ code: pointers, memory allocation, type safety, preprocessor • Tries to be more Object-Oriented: everything is in a class • Tries to be easier and simpler than C++ • Tries to be amenable to large projects worked on by worker-bee programmers

6. Java as a Worse C++ • Slow, slow, and slow compared w/ C/C++ • Despite garbage collection, you can still have memory problems • Neither C++ nor Java retains backward compatibility w/ old code. • Ridiculous class libraries...complex operations for simple tasks. • Have to use their package/directory structure...like it or not.

7. Java Hello World public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World"); } } • Must be in a HelloWorld.java • Each .java can have its own main() • Compile .java to .class with javac • Run .class with java, or build a .jar

8. Java Hello World • Notice how you can't write code outside a class, and can't write a class except in its proper file...but you are able to run main() even though there is no instance of class HelloWorld. • Static class functions fly in the face of “pure OOP”. Also, Java's built-in types (like int) are not objects, so “more pure than C++” does not mean “pure OO”

9. Java Types • byte, short, int, long, float, double, boolean, char (16-bit, Unicode) • Precision/size generally guaranteed across platforms • Arrays – size fixed at creation • Objects – instances of a class. Lots of important standard classes, like strings