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1
CISC6795: INTERNET
COMPUTING AND JAVA
PROGRAMMING
Xiaolan Zhang
Spring 2011
Course Objectives
2



Basic programming concepts in Java language
Object-oriented approach to software design and
development
Java APIs including
 Java
Collection API
 Graphical User Interface packages
 Database connectivity (JDBC)
 Web application (applet)


Design and implement medium-size standalone and
web applications
Assume some knowledge of C++ or C programming
Reference textbook
3

Thnking in Java, Bruce Eckel,
 Free
Electronic Version
 Great for someone with C/C++ programming
experience

Java How to Program, H.M. Deitel and P.J. Deitel, 8th
Edition, Prentice Hall, late object version
 For

beginner programmers
We take late object approach
 i.e.,
we first focus on basic programming constructs
Focus and philosophy
4

Software reuse: building-block approach to create
programs.
 Avoid
reinventing the wheel—use existing pieces
wherever possible.
 Building blocks: classes from class libraries, classes you
wrote before, and classes that others create and make
available to you (many are available over Internet for
free)
Focus and philosophy (2)
5

Benefits of software reuse:
 save
program development time
 often improve program performance (as libraries
carefully written to perform efficiently)

To use building blocks
 Read
documentation for the version of Java
 Refer
to it frequently to be sure you are aware of the rich
collection of Java features and are using them correctly.
 When in doubt, experiment and see what happens.
Online resource
6
•
•
http://www.oracle.com/technetwork/java/index.ht
ml : official info. about Java including
documentation, software, announcements, tutorials,
and much more.
In particular, class library documentation at
http://download.oracle.com/javase/1.4.2/docs/api/
•
Download a zip or tar file and install it on your own PC.
History of Java
7



Originally for intelligent consumer-electronic devices in Sun
Microsystems (1990)
Reason: C++ not a good fit:
 Demanded too large a footprint
 Its complexity led to developer errors
 No garbage collection, programmers managing system
memory => challenging and error-prone
 Lack of portable support for security, distributed
programming, and threading
 Could not be easily ported to all types of devices
Now: large-scale enterprise applications, Web program,
consumer devices (cell phones, etc.)
Memory footprint
8

Memory footprint: the amount of main memory that
a program uses or references while running.
 Includes
code, static data sections (both initialized and
uninitialized), heap, stacks
 structures introduced by run-time environment
(compiler, interpreter, Java Virtual Machine): such as
symbol tables, constant tables, debugging structures,
open files
 Those that program ever needs while executing and will
be loaded at least once during entire run.
Java as a platform
9
•
•
Java is a platform for application development
Typically, a platform means some combination of
hardware and system software that will mostly run all
same software.
–
–
•
e.g., PowerMacs running Mac OS 9.2
e.g., DEC Alphas running Windows NT
Problem:
–
Programs very closely tied to specific hardware and
operating system they run.
–
–
Program needs to be ported to different platforms
Distributing executable programs from web pages is hard
Platform Independence of Java
10
•
•
Java: write one, run everywhere
Java compiler (javac) produces byte code
• Byte code written in hexadecimal, byte by byte,
looks like this:
•
•
•
CA FE BA BE 00 03 00 2D 00 3E 08 00 3B 08 00 01 08 00 20 08
…
Byte code is exactly the same on every platform
Interpreter/Just-in-time compiler (java) translates
byte code to machine’s native language to
execute
•
Compiler is not platform independent
Platform Independence
11
•
Only interpreter/JIT compiler and a few native
libraries need to be ported to get Java to run on
a new computer or operating system
•
•
The rest of the runtime environment, compiler and most
of class libraries are written in Java.
javac compiler, java interpreter, Java
programming language, and more are
collectively referred to as Java.
The Scope of Java
12



J2SE
J2EE
J2ME
One Java Platform, Multiple Profiles
Java Profiles
13

Java Card: allows small Java-based applications to
run securely on smart cards and similar smallmemory-footprint devices
 Smart
card, chip card, or integrated circuit card, is any
pocket-sized card with embedded integrated circuits,
for providing identification, authentication, data
storage and application processing

Java ME (Micro Edition): for devices which are
sufficiently limited
 Supplying
full set of Java libraries would take up
unacceptably large amounts of storage.
Java Profiles (cont’d)
14


Java SE (Standard Edition): For general-purpose
use on desktop PCs, servers and similar devices.
Java EE (Enterprise Edition): Java SE plus various
APIs useful for multi-tier client–server enterprise
applications
15
Life-cycle of Java Program
javac welcome1.java
java welcome1
16
17
Introduction to Java Programming
18

We demonstrate how to:
 Display
messages
 Obtain information from the user
 Arithmetic calculations
 Decision-making fundamentals
 A quick start, and Illustrates several important Java
language features
1
// Fig. 2.1: Welcome1.java
2
// Text-printing program.
19
3
4
public class Welcome1
5
{
6
// main method begins execution of Java application
7
public static void main( String args[] )
8
{
9
System.out.println( "Welcome to Java Programming!" );
10
11
} // end method main
12
13 } // end clazss Welcome1
Welcome to Java Programming!
Line numbers not part of program,
added for reference
First Program in Java: Printing a Line of Text
(Cont.)
20
1
// Fig. 2.1: Welcome1.java
2
// Text-printing program.
 Comments
start with: //
 Comments
ignored during program execution
 Document and describe code
 Provides code readability
 Traditional
comments: begin with /*,end with */
/* This is a traditional
comment. It can be
split over many lines */
 No
space between / and *
Good Programming Practice
21

Every program should begin with a comment
that explains the purpose of the program, the
author and the date and time the program
was last modified.
Class declaration
22
3

Blank line


4

Makes program more readable
Blank lines, spaces, and tabs are white-space characters
 Ignored by compiler
public class Welcome1
Begins class declaration for class Welcome1



Every Java program has at least one user-defined class
Keyword: words reserved for use by the language (here, Java)
 class keyword must be followed by class name
Naming classes: capitalize every word, i.e., camel case
 SampleClassName
 Java
programmers know that such identifiers normally
represent Java classes, so naming your classes in this manner
makes your programs more readable.
Syntax Error
23


The syntax of a programming language specifies rules for
creating a proper program in that language.
A syntax error occurs when the compiler encounters code
that violates Java’s language rules (i.e., its syntax).
E.g., keyword class not followed by an identifier a syntax error
 When it happens, compiler does not generate .class file.
Instead, it issues an error message to help programmer identify
and fix incorrect code.
 also called compiler errors, compile-time errors or compilation
errors, because compiler detects them during compilation
phase.

Rules for identifier
24
4

public class Welcome1
Welcome1 is an example of identifier, name for
variable, class or method
 Series
of characters consisting of letters, digits,
underscores ( _ ) and dollar signs ( $ )
 Does not begin with a digit, has no spaces
 Examples: Welcome1, $value, _value, button7
 7button
 Java
 a1
is invalid
is case sensitive (capitalization matters)
and A1 are different
Class declaration (2)
25
public class Welcome1
4
 Important
rules:
 The
above code must be saved as file Welcome1.java, i.e.,
class name with .java extension
 Different from C++
5
{
 Left
brace {
 Begins
body of every class
 Right brace ends declarations (line 13)
It is an error not to end a file name with .java extension for
a file containing a class declaration.
Good Programming Practice
26

Whenever you type an opening left brace, {, in
your program
 immediately
type the closing right brace, },
 then reposition the cursor between the braces
 indent the entire body of class declaration
 i.e.,
begin lines with the body by a fixed number of spaces,
or a tab


Prevent missing or unmatching braces, a syntax error
Indentation emphasizes class declaration's structure
and makes it easier to read.
27
Good Programming Practice:
indentation


Set a convention for indent size you prefer
Uniformly apply that convention.
 use
Tab key may be used to create indents, but tab
stops vary among text editors.
 use three spaces to form a level of indent.
main method
28
public static void main( String args[] )
7

Part of every Java application



Methods can perform tasks and return information


void means main returns no information
For now, mimic this line in your program
{
8

Applications begin executing at main
 Parentheses indicate main is a method (Ch. 3 and 6)
 Java applications contain one or more methods
Exactly one method must be called main
Left brace begins body of method declaration

Ended by right brace } (line 11)
Good Programming Practice
29

Similar to class declaration, for a method:
 the
body of the method declaration starts with left
brace, {, and ends with right brace, }
 Indent entire body of each method declaration one
“level” of indentation
 Makes structure of codes stand out
Statement
30
System.out.println( "Welcome to Java Programming!" );
9

Statement: instructs computer to perform an action



System.out


Prints string of characters
 String - series characters inside double quotes
White-spaces in strings are not ignored by compiler
Standard output object, usually pointing to command window (i.e.,
MS-DOS prompt, or PuTTy window)
Method System.out.println

Displays a line of text
 Statements
 Omitting
must end with semicolon ;
semicolon at end of a statement is a syntax error.
Error-Prevention Tip
31

When learning how to program, try “break” a
working program to familiarize yourself with
compiler's syntax-error messages.
 E.g.
remove a semicolon or brace, see error
messages incurred

Syntax error messages not always give exact
position or problem in the code.
 Cascading
effects …
 Check reported line first, and then check preceding
lines for syntax errors
First Program in Java: Printing a Line of Text
(Cont.)
32
11
} // end method main
 Ends
13
method declaration
} // end class Welcome1
 Ends
class declaration
 Comments are added to keep track of ending braces
To improve readability, follow closing right brace (}) of a method
body or class declaration with an end-of-line comment indicating
the method or class declaration to which the brace belongs.
Compile Java program
33



From a command prompt window, go to directory
where program is stored
Type javac Welcome1.java
If no syntax errors, Welcome1.class created
 Has
bytecodes that represent application
Possible error messages
34

“bad command or filename,” or “javac: command not
found” or “'javac' is not recognized as an internal or
external command, operable program or batch file,”

your Java software installation was not completed properly

E.g. system’s PATH environment variable was not set properly

Review J2SE Development Kit installation instructions at
java.sun.com/j2se/5.0/install.html
Interpret syntax-error messages
35

Each syntax-error messages contains file name
and line number where an error is detected.
 E.g., Welcome1.java:6
refers to Welcome1.java at
line 6.
 Remainder of error message provides
information about the syntax error.
Common compiler error message
36

“Public
class
a file called
 The
ClassName must be
ClassName.java”
defined in
file name does not match the name of the
public class in the file
Execute Your First Java Program
37

From terminal window (e.g., Putty) or command
prompt (of Windows), type java Welcome1
 Launches
Java Virtual Machine
 JVM loads .class file for class Welcome1
 .class
 JVM
extension omitted from command
execute the program by calling method main of
the class
Common error message
38

“Exception in thread "main"
java.lang.NoClassDefFoundError: Welcome1,”
 Your
CLASSPATH environment variable has not been set
properly.
 See related slide before
1
// Fig. 2.3: Welcome2.java
2
// Printing a line of text with multiple statements.
39
print vs println
3
4
public class Welcome2
5
{
6
// main method begins execution of Java application
7
public static void main( String args[] )
8
{
9
System.out.print( "Welcome to " );
10
System.out.println( "Java Programming!" );
11
12
} // end method main
13
14 } // end class Welcome2
Welcome to Java Programming!
System.out.print keeps the
cursor on the same line, so
System.out.println continues
on the same line.
Display special characters
40



How to display special characters, such as doublequote, newline, … ?
Use escape character which starts with backslash (
\ ) to indicate special character
E.g., newline characters (\n)
 Indicates
cursor should be at the beginning of the next
line
9
 Line
System.out.println( "Welcome\nto\nJava\nProgramming!" );
breaks at \n
1
// Fig. 2.4: Welcome3.java
2
// Printing multiple lines of text with a single statement.
3
4
public class Welcome3
5
{
6
// main method begins execution of Java application
7
public static void main( String args[] )
8
{
9
System.out.println( "Welcome\nto\nJava\nProgramming!" );
10
11
} // end method main
12
13 } // end class Welcome3
Welcome
to
Java
Programming!
Notice how a new line is output for each
\n escape sequence.
Some common escape sequences
42
Escape Description
sequence
\n
Newline. Position the screen cursor at the beginning of the next line.
\t
\r
Horizontal tab. Move the screen cursor to the next tab stop.
Carriage return. Position the screen cursor at the beginning of the
current line—do not advance to the next line. Any characters output
after the carriage return overwrite the characters previously output
on that line.
Backslash. Used to print a backslash character.
Double quote. Used to print a double-quote character. For example,
System.out.println( "\"in quotes\"" );
displays
"in quotes"
\\
\"
Displaying Text with printf
43

System.out.printf
 Displays
formatted data
System.out.printf( "%s\n%s\n",
"Welcome to", "Java Programming!" );
9
10
 First
parameter is format string, a string made up of
 Fixed
text, e.g., \n in above example
 Format specifier – placeholder for a value, specify the
type and format for each subsequent paramters

Format specifier %s – placeholder for a string
1
// Fig. 2.6: Welcome4.java
2
// Printing multiple lines in a dialog box.
3
4
public class Welcome4
5
{
6
// main method begins execution of Java application
7
public static void main( String args[] )
8
{
9
10
System.out.printf( "%s\n%s\n",
"Welcome to", "Java Programming!" );
11
12
} // end method main
13
14 } // end class Welcome4
Welcome to
Java Programming!
System.out.printf
displays formatted data.
Good Programming Practice
45


Place a space after each comma (,) in an
argument list to make programs more
readable.
Long statement can be split into multiple lines
 Indent
all subsequent lines of the statement
 Splitting in the middle of an identifier or a string
is a syntax error.
Second Java Application: Adding Integers
46

Upcoming program
 Use
Scanner to read two integers from user
 Use printf to display sum of the two values
 Use packages
1
// Fig. 2.7: Addition.java
2
// Addition program that displays the sum of two numbers.
3
import java.util.Scanner; // program uses class Scanner
import declaration imports class
Scanner from package

java.util.
4
5
public class Addition
6
{
Outline
47
7
// main method begins execution of Java application
8
public static void main( String args[] )
9
{
Declare and initialize
 (1 variable
of 2)
input, which is a Scanner.
import
10
// create Scanner to obtain input from command window
11
Scanner input = new Scanner( System.in );
12
13
int number1; // first number to add
14
int number2; // second number to add
15
int sum; // sum of number1 and number2
Addition.
java
declaration

Scanner

nextInt
Declare variables
number1, number2 and
sum.
16
17
System.out.print( "Enter first integer: " ); // prompt
18
number1 = input.nextInt(); // read first number from user
19
Read an integer from the user
and assign it to number1.
Outline
48
20
System.out.print( "Enter second integer: " ); // prompt
21
number2 = input.nextInt(); // read second number from
Readuser
an integer
22
23
24
25
26
27
from the
user and assign it to
number2.

Additi
Calculate the sum
of the
on.jav
System.out.printf( "Sum is %d\n", sum ); // display
sum
variables
number1 and
a result to
number2, assign
sum = number1 + number2; // add numbers
} // end method main
sum.
28

(2 of 2)

4. Addition
Display the sum using
5. printf
formatted output.
29 } // end class Addition
Enter first integer: 45
Enter second integer: 72
Sum is 117
Two integers entered by the
user.
Second Java Application: Adding Integers (Cont.)
49
3
import java.util.Scanner;
 import
// program uses class Scanner
declarations
 Used
by compiler to identify and locate classes used in Java
programs
 Tells compiler to load class Scanner from java.util
package
5
6
public class Addition
{
 Begins
public class Addition
 Recall
 Lines
that file name must be Addition.java
8-9: begins main
Common Programming Error
50


All import declarations must appear before the
first class declaration in the file. Placing an
import declaration inside a class declaration’s
body or after a class declaration is a syntax
error.
Forgetting to “import” a class used in your
program typically results in compilation error
such as “cannot resolve symbol.”
 Make
sure to provide proper import declarations
Variable declaration statement
51
10
11

// create Scanner to obtain input from command window
Scanner input = new Scanner( System.in );
Variables


Location in memory that stores a value
 Declare with name and type before use
input is of type Scanner,a class that enables a program to
read data from keyboard
 Variable name: any valid identifier (recall the rule?)
 Declarations end with semicolons ;
 Initialize variable in its declaration



Equal sign stands for assignment operator
The parameter System.in refers to standard input object (often links to
keyboard)
The input variable will be used to read inputs from keyboard
Primitive types
52
int number1; // first number to add
int number2; // second number to add
int sum; // second number to add
13
14
15

Declare variable number1, number2 and sum of type int





int holds integer values (whole numbers): i.e., 0, -4, 97
Types float and double hold decimal numbers
Type char holds a single character: i.e., x, $, \n, 7
int, float, double and char are primitive types
Comments to describe purpose of variables
int number1, // first number to add
number2, // second number to add
sum; // second number to add


Can declare multiple variables of the same type in one declaration
Use comma-separated list
Good Programming Practice
53

Declare each variable on a separate line
 allows
a descriptive comment to be easily
inserted next to each declaration.

Choose meaningful variable names
 self-documenting

program
Convention for variable-name identifiers
 begin
with a lowercase letter, and every
subsequent word in the name begins with a
capital letter
 e.g., firstNumber, studentRecord, …
Second Java Application: Adding Integers (Cont.)
54
System.out.print( "Enter first integer: " ); // prompt
17
 Message
called a prompt - directs user to perform an
action
18
number1 = input.nextInt(); // read first number from user
 Result
of call to nextInt given to number1 using
assignment operator =
 Assignment
statement
 = binary operator - takes two operands

Expression on right evaluated and assigned to variable on left
 Read
as: number1 gets the value of
input.nextInt()
55
Software Engineering Observation 2.1

By default, package java.lang is imported
in every Java program; thus, java.lang is
the only package in the Java API that does
not require an import declaration.
Good Programming Practice
56

Place spaces on either side of a binary
operator to make it stand out and make the
program more readable.
Another Java Application: Adding Integers
(Cont.)
57
20
System.out.print( "Enter second integer: " ); // prompt
 Similar
to previous statement
 Prompts
21
number2 = input.nextInt(); // read second number from user
 Similar
to previous statement
 Assign
23
the user to input the second integer
variable number2 to second integer input
sum = number1 + number2; // add numbers
 Assignment
 Calculates
statement
sum of number1 and number2 (right hand
side)
 Uses assignment operator = to assign result to variable sum
 Read as: sum gets the value of number1 + number2
 number1 and number2 are operands
Another Java Application: Adding Integers
(Cont.)
58
System.out.printf( "Sum is %d\n: " , sum ); // display sum
25
 Use
System.out.printf to display results
 Format specifier %d
 Placeholder
for an int value
System.out.printf( "Sum is %d\n: " , ( number1 + number2 ) );
 Calculations
can also be performed inside printf
 Parentheses around the expression number1 +
number2 are not required
Variables stored in memory
59


Variable has a name, a type, a size and a value
Variables are stored in main memory
 Size
of memory depends on the type
 Name corresponds to location in memory
 Mapping


performed by compiler
Assignment statement: place new value into
variable, replaces (and destroys) previous value
Reading variables from memory does not change
them
Illustration of variables in memory
60
Arithmetic Expression
61

Arithmetic calculations used in most programs
 Usage
for multiplication
 / for division
 % for remainder
 +, *
 Integer
division truncates remainder
7 / 5 evaluates to 1
 Remainder
operator % returns the remainder
7 % 5 evaluates to 2
Arithmetic operators
62
Java
operation
Arithmetic Algebraic
operator
expression
Java
expression
Addition
+
f+7
f + 7
Subtraction
–
p–c
p - c
Bm
b * m
Multiplication *
Division
/
x / y or
or x ÷ y
x / y
Exercise: write an expression to convert temperature from
Farenheith degree to Celsus degree:
Hint: Tf = (9/5)*Tc+32;
Tc = temperature in degrees Celsius
Tf = temperature in degrees Fahrenheit
Operator Precedence
63

Some arithmetic operators act before others (i.e.,
multiplication before addition)
 Use

parenthesis when needed
Example: Find the average of three variables a, b
and c
 Do
not use: a + b + c / 3
 Use: ( a + b + c ) / 3
Precedence of arithmetic operators
64
Operator(s) Operation(s) Order of evaluation
(precedence)
*
Multiplication
/
Division
%
Remainder
+
Addition
-
Subtraction
Evaluated first. If there are
several operators of this type,
they are evaluated from left to
right.
Evaluated next. If there are
several operators of this type,
they are evaluated from left to
right.
Good Programming Practice
65

Refer to operator precedence chart when
writing expressions containing many operators.
 Confirm
that the operations in the expression are
performed in the order you expect.


When uncertain, use parentheses to force the
order, exactly as you would do in algebraic
expressions.
Some operators, such as assignment, =,
associate from right to left rather than from left
to right.
Evaluation order of a second-degree polynomial
66
Decision Making: Equality and Relational
Operators
67


if statement (Simple version here, more detail later)
if (condition)
body
 If the condition is true, then the body of the if
statement executed
 Execute resumes at statement after the if statement
Condition: expression that is either true or false
 can

be formed using equality or relational operators
Body of the if statement can be:
A
single statement
 A block of statement
Equality and relational operators
68
Standard algebraic Java equality Sample
equality or relational or relational Java
operator
operator
condition
Equality operators


Relational operators



≤
Meaning of
Java condition
==
!=
x == y
x != y
x is equal to y
x is not equal to y
>
<
>=
<=
x
x
x
x
x is greater than y
x is less than y
x is greater than or equal to y
x is less than or equal to y
> y
< y
>= y
<= y
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// Fig. 2.15: Comparison.java
// Compare integers using if statements, relational operators
// and equality operators.
import java.util.Scanner; // program uses class Scanner
69
public class Comparison
{
// main method begins execution of Java application
public static void main( String args[] )
{
// create Scanner to obtain input from command window
Scanner input = new Scanner( System.in );
int number1; // first number to compare
int number2; // second number to compare
System.out.print( "Enter first integer: " ); // prompt
number1 = input.nextInt(); // read first number from user
System.out.print( "Enter second integer: " ); // prompt
number2 = input.nextInt(); // read second number from user
if ( number1 == number2 )
System.out.printf( "%d == %d\n", number1, number2 );
Test for equality, display
result using printf.
if ( number1 != number2 )
System.out.printf( "%d != %d\n", number1, number2 );
if ( number1 < number2 )
System.out.printf( "%d < %d\n", number1, number2 );
Compares two numbers
using relational operator
<.
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if ( number1 > number2 )
System.out.printf( "%d > %d\n", number1, number2 );
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if ( number1 <= number2 )
System.out.printf( "%d <= %d\n", number1, number2 );
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if ( number1 >= number2 )
System.out.printf( "%d >= %d\n", number1, number2 );
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} // end method main
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43 } // end class Comparison
Enter first integer: 777
Enter second integer: 777
777 == 777
777 <= 777
777 >= 777
Enter first integer: 1000
Enter second integer: 2000
1000 != 2000
1000 < 2000
1000 <= 2000
Enter first integer: 2000
Enter second integer: 1000
2000 != 1000
2000 > 1000
2000 >= 1000
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Compares two numbers
using relational operator
>, <= and >=.
Decision Making: Equality and Relational
Operators (Cont.)
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 Line
6: begins class Comparison declaration
 Line 12: declares Scanner variable input and assigns it
a Scanner that inputs data from the standard input
 Lines 14-15: declare int variables
 Lines 17-18: prompt the user to enter the first integer
and input the value
 Lines 20-21: prompt the user to enter the second
integer and input the value
Decision Making: Equality and Relational
Operators (Cont.)
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if ( number1 == number2 )
System.out.printf( "%d == %d\n", number1, number2 );
23
24
 if
 If
statement to test for equality using (==)
variables equal (condition true)

Line 24 executes
 If
variables not equal, statement skipped
 Empty statement

 Lines
No task is performed
26-27, 29-30, 32-33, 35-36 and 38-39
 Compare
number1 and number2 with the operators !=,
<, >, <= and >=, respectively
Common Programming Error
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
Confusing equality operator, ==, with assignment
operator, =, leads to logic error or syntax error.
== read as “is equal to”
 = read as “gets”, or “gets the value of.”




It is a syntax error to add spaces between symbols
in operators ==, !=, >= and <=
Reversing operators !=, >= and <=, as in =!, =>
and =<, is a syntax error.
Placing a semicolon immediately after right
parenthesis of condition in an if statement is
normally a logic error.
Assignments
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
You can choose to set up Java environment on your
own computer
 (Optional)
Download and install Eclipse IDE for Java at
http://www.eclipse.org/downloads/
 Download and install Java Runtime Environment at
 Use
info. at the following page to decide which version to
download:
http://www.eclipse.org/downloads/moreinfo/jre.php

Lab1 assignment
Acknowledgement
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
Parts of the slides are adapted from powerpoint s
slides for Java How To Program, 1992-2010 by
Pearson Education, Inc. All Rights Reserved.