CPE-101

1. CPE-101 Clark Savage Turner, J.D., Ph.D. csturner@csc.calpoly.edu 756-6133 Slides adapted for use with Kaufman and Wolz by Clark S. Turner, and Some lecture slides were adapted from those developed by John Lewis and William Loftus to accompany Java Software Solutions, 2d ed. Some slides adapted from slides by Carol Scheftic, Cal Poly CSC Dept.

2. Focus of the course • Object-oriented software development • problem solving • program design and implementation • object-oriented concepts • objects • classes • interfaces • inheritance • polymorphism • graphics and Graphical User Interfaces • the Java programming language

3. Programs are written to solve problems! • The general steps in problem solving are: • Understand the problem • What is the problem? What is not part of the problem? • Dissect the problem into manageable pieces. • Design a solution • Have you seen this problem before? Have you seen a similar one? • Can you restate the problem? Can you solve it? Part of it? • Consider alternatives to your first solution and refine it. • Implement the solution • Check each step as you proceed. Test the final solution. • If necessary, fix any problems that exist, and repeat the previous step. • Reflect on what you learned from the problem • What did you learn from the problem? the solution? • What did you learn from any difficulties you encountered?

4. More on Problem Solving • Many software projects fail because the developer didn't really understand the problem to be solved. • We must avoid assumptions and clarify ambiguities. • As problems and their solutions become larger, we must organize our development into manageable pieces. • This technique is fundamental to software development. • We will dissect our solutions into pieces called classes, objects and methods, taking an object-oriented approach.

5. Brief Java History • 1990-95: James Gosling at Sun began to develop a new programming language for consumer electronics software. • It was originally known as Oak • It was small, reliable, and architecture independent. • 1990-94: Tim Berners-Lee at CERN in Geneva began to develop the World Wide Web. • It was powerful, global, and architecture independent. • ~1993: The Java team wrote a browser called HotJava. • It was the first web browser to support Java applets. • It demonstrated the power of Java to the rest of the programming world.

6. But what is Java? • A high-level programming language. • Object-oriented. • Architecture-neutral and portable. • Sort of interpreted, sort of compiled. • CAUTION: • 101-102-103 now focus on object-oriented (OO) design. • C++ permits an OO approach, but... • Java REQUIRES an OO approach!

7. Interpret or Compile? • BASIC is interpreted: • High-level source code is run by an interpreter on a specific microprocessor. • Every time the program is run, it must be re-interpreted. • C and C++ are compiled: • High level source code is run through a compiler. • Each compilation is specific to a given microprocessor. • To run the program, you run the appropriate compiled code. • Java is a hybrid: • High level source code is run through a compiler to create bytecode. • To run the bytecode, you can: • Interpret that through a specific Java bytecode interpreter, OR • Compile that into specific machine-code.

8. Compilers and Interpreters • We write source code files in the Java language. Human beings can read those files. • We then compile the source file down to Java bytecode using a Java compiler: • javac MyFile.java yields MyFile.class • Our Java bytecode file can be run in one of two ways: • It can be run on a Java interpreter. • It can be further compiled to native machine code for a particular machine.

9. Executing a Java Program • When someone invokes the java MyFile command... • The Java runtime environment first invokes a class loader. • The class loader loads the bytecodes for all the required classes from disk. • Once they are loaded, two operations are performed: • A bytecode verifier confirms that all bytecodes are valid. • All bytecodes are checked to see that they do not violate Java’s security restrictions. • The bytecodes are then passed to: • A Java interpreter, • Or to a Java just-in-time compiler (faster execution).

10. Browser Applet Interpreter Java Translation and Execution Java source code Java bytecode Java compiler Java program interpreter Bytecode compiler Machine code

11. Programming Language Levels • Four levels of programming language: • machine language • assembly language • high-level language • procedural (e.g., Algol, Basic, C, Cobol, Fortran, Interlisp, Pascal) • functional (e.g., APL, Lisp, Scheme) • parallel (e.g., High Performance Fortran, Linda) • logic (e.g., Duck, Prolog) • combos (e.g., procedural+parallel—Ada or procedural+OO—Loops) • object-oriented (e.g., C++, Java, Scheme, Visual Basic) • fourth-generation language • Each type of CPU has its own specific machine language • The levels beyond that were created to make it easier for a human being to write programs

12. Java Development Environments • There are many development environments that develop Java software: • Sun Java Software Development Kit (SDK) • Borland JBuilder • MetroWork CodeWarrior • Symantec Café • Microsoft Visual J++ • Though the details of these environments differ, the basic compilation and execution process is essentially the same.

13. Syntax and Semantics • The syntax rules of a language define how we can put symbols, reserved words, and identifiers together to make a valid program. • The semantics of a program statement define what that statement means (its purpose or role in a program). • A program that is syntactically correct is not necessarily logically (semantically) correct. • A program will always do what we told it to do, not what we meant to tell it to do.

14. Java Program Structure • In the Java programming language: • A program is made up of one or more classes • A class contains one or more methods • A method contains program statements • These terms will be explored in detail throughout the course • A Java application always contains a method called main • (A Java applet does not…)

15. Java Program Structure // comments about the class public class MyProgram { } class header class body Comments can be added almost anywhere

16. Java Program Structure // comments about the class public class MyProgram { } // comments about the method public static void main (String[] args) { } method header method body

17. Identifiers • Identifiers are the words a programmer uses in a program. • An identifier can be made up of letters, digits, the underscore character (_), and the dollar sign. • They cannot begin with a digit. • Java is case sensitive, therefore Total and total are different identifiers. • this makes for many simple to make, hard to find, errors

18. Identifiers • Sometimes we choose identifiers ourselves when writing a program. • Sometimes we are using another programmer's code, so we use the identifiers that they chose (such as println). • does it “come with the language”? • no, it is an example of reuse of code (“libraries”) • Often we use special identifiers called reserved words that already have a predefined meaning in the language itself. • a reserved word cannot be used in any other way.

19. Reserved Words • The Java reserved words: abstract boolean break byte byvalue case cast catch char class const continue default do double else extends false final finally float for future generic goto if implements import inner instanceof int interface long native new null operator outer package private protected public rest return short static super switch synchronized this throw throws transient true try var void volatile while

20. Comments • Comments in a program are also called inline documentation • They should be included to explain the purpose of the program and describe processing steps • They do not affect how a program works • Java comments typically take one of three forms: // this comment runs to the end of the line /* this comment runs to the terminating symbol, even across line breaks */ /** this comment form, which we will not * use yet, is for the javadoc system */

21. White Space • Spaces, blank lines, and tabs are collectively called white space. • White space is used to separate words and symbols in a program. • Extra white space is useful to humans, and ignored by machines. Use lots of it!!! (And curly braces too.) • A valid Java program can be formatted many different ways. • Programs should be formatted to enhance readability, using consistent indentation. • Coding standards are enforced for many projects • It is quite a serious business • consider code maintenance

22. Naming Conventions • Give identifiers semantic meaning. • Recall that programmers write identifiers for a purpose • How does this work with comments in the code? • Make identifiers easy to read: r versus radius • Follow consistent capitaliztion: • Use lowercase for variable and method names, except for the first letter of later words: currentTemperature • All reserved words must be in lower case. • Can you use a capitalized “reserved word” any way you like? Try this. Why would you ever want to do it? • Use Title Case for class, package, and interface names: TemperatureConverter • Use UPPERCASE for constants, separating words with an underscore: ABSOLUTE_ZERO

23. Three Types of Program Errors • Compile-time errors: problems with syntax and other basic issues that are found by the compiler. • If compile-time errors exist, an executable version of the program is not created • in our case, bytecode is not produced, right? • Run-time errors: a problem that occurs during program execution and causes a program to terminate abnormally, such as trying to divide by zero. • Logical Errors: a program may run, but still produce incorrect results. • What would you suspect “incorrect” means in this case?