TCU CoSc 10403 Introduction to Programming (with Java)

1
TCU CoSc 10403 Introduction to Programming (with
Java)

• Java Language Overview

2
Consider another simple HelloWorld program

• import javax.swing.
• import java.awt.
• /
• Another HelloWorld program in Java
• /
• public class HelloWorld extends JApplet
• JLabel helloLabel new JLabel ("How ya
  doing?")
• public void init()
• setLayout(new FlowLayout())
• add (helloLabel)
• helloLabel.setForeground (Color.RED)

3
Syntax Semantics

• Note that the preceding program contained a
  variety of different symbols ,/().
• These are delimiters (punctuation marks) in the
  language and must appear in particular places.
• Similarly, note that there are words such as
  (class, public, extends, import,
  Applet) - these are reserved words in the
  language and must not be misspelled or written in
  the wrong context.

4
Syntax Semantics

• The syntax of a language defines how you can put
  symbols, reserved words, and identifiers together
  to make a valid program.
• During compilation, all syntax rules are
  checked.
• If a program is not syntactically correct, the
  compiler gives error messages and wont produce
  the bytecode.
• Syntax errors must be eliminated before the
  bytecodes are produced that allows us to try to
  execute the program.
• The semantics of a language construct is the
  meaning of the construct it defines its role in
  a program
• A syntactically correct program does not mean it
  is logically (semantically) correct.
• A program will always do what it is told to do -
  not what the programmer meant to tell it to do.

5
Errors

• A program may have three different types of
  errors.
• Compile-time errors - errors with syntax (if
  compile-time errors exist, an executable version
  of the program is not created.
• Run-time errors program compiles starts to
  excute and then crashes (terminates abnormally)
  (Example divide by zero).
• Logical errors program compiles and
  executes.The program runs with no errors but
  produces incorrect results.

6
Problem Solving

• Debugging finding and fixing errors in code
• System.out.println prints to the console window
• use System.out.println statements to see where
  you are in the programs execution or to display
  the value of variables
• System.out.println( a )
• System.out.println( x x )
• These will display in the Console window at the
  bottom of the IDE

System.out.println information appears in the
Console window.
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Coding Style

• White Space
• Spaces, blank lines, and tabs are collectively
  called white space and are used to separate
  words and symbols in a program
• Extra white space is ignored
• A valid Java program can be formatted many
  different ways
• Programs should be formatted to enhance
  readability, using consistent indentation
• Poor examples

Choose some style (mine, the Authors) and
stick with it!!!
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Better Style

• /
  /
• / Program Name Lab 1 /
• / /
• / Student Name J.Q. Public /
• / Semester Spring, 2004 /
• / Class Section CoSc 10403 - 15 /
• / Instructor Dr. James Comer /
• / /
• / Program Overview /
• / This program displays a string of text in
  the center /
• / of the applet window. The text is drawn in
  blue in /
• / bold, 16 point Helvetica /
• / /
• / Input /
• / There is no input to this program. /
• / /
• / Output /
• / The string of text that is hard coded in
  the program. /
  
• / /

• White space consists of blanks, tabs, and newline
  characters.
• White space is used to separate the words and
  symbols used in Java programs.
• A programmer can use white space to emphasize
  parts of the program and to make the program
  easier to read.
• Except when its used to separate words, the
  computer ignores white space.

9
Documentation

• All programs are to be documented using the
  Documentation Guidelines and the Documentation
  Standard provided on the 10403 class website.
• Failure to do so will result in several lost
  points on your graded lab assignment.
• Comments should include a detailed preamble set
  of comments (see the standard) and inline
  documentation (to explain the purpose of the
  program and to describe processing steps). These
  are to be positioned within the executable
  statements of your program.
• Java comments (which are ignored by the compiler)
  can take two forms
• // comment runs to the end of the line
• and
• / The purpose of this program is ..
• ../

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Documentation Standard

• /
  
  /
• / Program Name Lab 3
  
  /
• /
  
  /
• / Student Name John Q. Programmer
  
  /
• / Semester Fall, 1999
  
  /
• / Class Section CoSc 10403 - 15
  
  /
• / Instructor Dr. Hallie Pena
  
  /
• / Due Date September 23, 1999
  
  /
• /
  
  /
• / Program Overview
  
  /
• / This applet uses a text field to accept
  user input representing a Fahrenheit temperature.
  /
• / When the user presses the ltenter keygt,
  the temperature is converted to Celsius. the
  /
• / result is displayed in a label and, in
  addition, in a text area that serves as an
  ongoing /
• / log of all conversions that have been
  performed. The user can continue to perform
  /
• / terperature conversions until the applet
  is terminated.
  /
• /
  
  /
• / Input
  
  /
• / Input data must be the integer Fahrenheit
  value that is to be converted to Celsius.
  /
• /
  
  /

11
Terminology for the parts of a Java program
A java
program
consists of
classes
consist of
members (instances of the class)
are
fields
methods
are
variables
objects
void
typed
consist of
declared with
classes
types
fields
statements
constructors
inner classes
are
parameters
are
invocation assignment repetition selection excepti
on
are
special typed methods
fields