Transcript TCU CoSc 10403 Programming with Java

TCU CoSc 10403
Introduction to Programming
(with Java)
Java Language Overview
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);
}
}
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.
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 won’t 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.
Errors
A program may have three different types of errors.
1. Compile-time errors - errors with syntax (if
compile-time errors exist, an executable version
of the program is not created.
2. Run-time errors – program compiles – starts to
excute and then crashes (terminates abnormally)
(Example: divide by zero).
3. Logical errors – program compiles and
executes.The program runs with no errors but
produces incorrect results.
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
program’s 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.
6
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
Author’s) and stick with it!!!
Better Style
• 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 it’s used to
separate words, the
computer ignores white
space.
/********************************************************************/
/*
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.
*/
/*
*/
/*
Program Limitations:
*/
/*
The text is centered only if the window is 200 x 200.
*/
/*
*/
/*
Significant Program Variables:
*/
/*
None
*/
/*
*/
/********************************************************************/
import java.awt.*;
import javax.swing.*;
Import java.applet.;
public class MyApplet extends JApplet
{
public void init()
{
repaint();
}
public void paint(Graphics g)
{
g.setFont(new Font("Helvetica", Font.BOLD, 16));
g.setColor(Color.blue);
g.drawString("Texas Christian University", 5, 100);
}
}
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 ……………..
…………………………………………………
………………………………………………..*/
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 <enter key>, 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.
*/
/*
*/
/* Output:
*/
/*
The corresponding Celsius value for the given input data. Past conversions are displayed */
/*
in a scrollable text area at the bottom of the display window.
*/
/*
*/
/* Program Limitations:
*/
/*
(1) only integer Fahrenheit values may be input for conversion.
*/
/*
(2) care should be taken when inputing values to be converted as the previous input value */
/*
remains in the input textfield until erased.
*/
/*
*/
/* Significant Program Variables:
*/
/*
title
- holds the title that is displayed at the top of the display window. */
/*
question
- holds the string that is displayed as the user prompt.
*/
/*
. . .
*/
/*
*/
/* References:
*/
/*
(1) this program originally appeared in: "Java Software
*/
/*
Solutions", John Lewis and William Loftus, Addison-Wesley,
*/
/*
1998, pp. 375-377.
*/
/***************************************************************************************************/
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
types
classes
fields
constructors
are
special typed
methods
parameters
are
fields
statements
are
invocation
assignment
repetition
selection
exception
inner
classes