CPE-101

1
CPE-101

• Clark Savage Turner, J.D., Ph.D.
• csturner_at_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.

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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

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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?

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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.

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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.

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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!

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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.

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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.

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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 Javas security restrictions.
• The bytecodes are then passed to
• A Java interpreter,
• Or to a Java just-in-time compiler (faster
  execution).

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Java Translation and Execution
Java source code
Java bytecode
Java compiler
Java program interpreter
Bytecode compiler
Machine code
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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., proceduralparallelAda or
  proceduralOOLoops)
• 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

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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.

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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.

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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)

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Java Program Structure
// comments about the class
public class MyProgram

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

// comments about the method
public static void main (String args)

method header
method body
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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

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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.

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Reserved Words

• The Java reserved words

abstract boolean break byte byvalue case cast catc
h char class const continue
default do double else extends false final finally
float for future generic
goto if implements import inner instanceof int int
erface long native new null
operator outer package private protected public re
st return short static super switch
synchronized this throw throws transient true try
var void volatile while
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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 /
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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

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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

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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?