CSE 1341 - Honors Principles of Computer Science I

1. CSE 1341 - HonorsPrinciples of Computer Science I Spring 2008 Mark Fontenot mfonten@engr.smu.edu Note Set 22

2. Note Set 21 Overview • Creating packages in Java • Wrap up • What else can you do now?

3. Packages • We’ve done a good deal of • import java.util.*; • import javax.swing.*; • What does that mean really? • Every class belongs to a package • Packages • contain groups of related classes • help organize code base of complex applications • facilitate software reuse • help prevent class-name conflicts

4. Steps for Declaring Reusable Class Declare a class public. If class not public, can only be used by other classes in same package. Choose unique name and add package declaration to source file package edu.smu.cse.mef; Compile class so that directory structure is createdNetbeans does this automatically for source and compiled version Use code elsewhere

5. Example Student.java package edu.smu.cse.mef; public class Student { private String name; private String id; private int test1; private int test2; public Student(String n, String i, int t1, int t2) { name = n; id = i; test1 = t1; test2 = t2; } }

6. Directory Structure

9. Importing the class that was created

10. Import Types • Single-type-import declaration • specifies exactly one class to import • import java.util.Scanner; • Type-Import-On-Demand Declaration • Allows all classes from a package to be accessed and used • import java.util.*;

11. What else is there? • What else is there beyond Java? • Some say there are over 2000 (!!!!) programming languages in existence. • Why learn to program? • computers are dumb • they need to be told exactly what to do – step by step • Programming is a tool • Few people program just to earn “cool” points • Use a computer to solve a particular problem – must tell it what to do

12. Why? Computers are nearly ubiquitous Think of a scenario where you can exists for 7 days with out interaction of a computer OR without interaction with anything that was influenced or designed by a computer!!!! Computers/processors are all over the place….They all need software to run so that they perform useful work

13. What else can Java do? • Create apps for portable devices/embedded devices • J2ME – Java 2 Micro Edition • examples: mobile phones, PDAs, TV set-top boxes, printers • Create web-based services and next-gen web applications • J2EE – Java 2 Enterprise Edition • Examples: E-commerce websites • Access web-services and APIs • Google API • YouTube API • Facebook API

16. What is possible? Finding Cures for Diseases? Enabling the disabled? Speeding up the Internet? Developing the next great web-app? Solving world hunger?

17. Examples • Bioinformatics/Computational Biology • Using computer science and algorithms to solve biologically relevant problems • Data Mining/Informatics • Effectively managing data and gleaning information from raw data • Computer Aided Design (not drawing houses) • Using computers to design computers • Optimization Issues (OR and CS) • UPS reduces number of left turns to save fuel.

18. Other Languages – C# C# Code using System; class A{ public static void Main(String[] args){ Console.WriteLine("Hello World"); } } Java Code class B{ public static void main(String[] args){ System.out.println("Hello World"); } } C# Code String csString = "Apple Jack"; csString.ToLower(); Java Code String jString = "Grapes"; jString.toLowerCase();

19. Other Languages – C++ int main () { string s; s = “Hello”; stack<char> stk; for (inti = 0; i < s.size(); i++) stk.push(s[i]); while (!s.isEmpty()){ cout << stk.top(); stk.pop(); } return 0; }