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CS591x
A very brief introduction to Java
Java
Java
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Developed by Sun Microsystems
was intended a language for embedded
applications
became a general purpose language
designed to support network programming
Java
Java is a semi-compiled language
Java compiler produces bytecode
Bytecode not executable by itself like a
binary executable (… except…)
Must run Java bytecode in an execution
environment
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Java Virtual Machine – JVM
This give Java programs portability
Java
Must download and install Java
Software Developers Kit (SDK)
A lot of kinds of Java out there
You want J2SE 1.4.2 SDK
Download it from java.sun.com
install
You may want a Java IDE
Java - Installation
Installation should be straight-forward
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download
open the installer package
see installation instructions on
java.sun.com/j2se
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Follow installation instructions/answer
questions
Java
Java SDK comes with a number of tools
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Java compiler
 javac myprogram.java
 compiler produces class files
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Java runtime environment (JVM)
 java myprog
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Java Archiver – jar
 jar cvf myjar.jar myprog.class ….
Java – Basic Syntax
public class myprog
{
public static void main(String[] args)
{
System.out.println(“Hello from myprog”);
}
}
Java – Basic syntax
a Java program must start with a class
name
class name must match the program’s
file name
compiler will produce a .class file with
the same name
Java – Basic syntax
Java programs contain classes and
methods
There are Java applications and Java
applets
A Java application must have a main
method
public static void main(String[] args){ … }
Java – Basic Syntax
Classes have zero or more properties
and zero or more methods
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properties are variables associated with
class
methods are procedures for operating on
the class, objects or properties
Objects are instances of classes
Java – sample program
public class sample {
public static void main(String[] args)
{
String str;
str = “first string”;
System.out.println(str);
str = “2nd string”;
System.out.println(str);
}
}
Java Data Types
chr – single unicode character
String – string of characters
int – integer
float – floating point number
boolean – boolean value
Java – Data Types
byte – single byte signed integer
short – two byte signed integer
long – very double precision integer
double – double precision float
Java
Arithmetic operators
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+ - * / % ++ -use parentheses to set precedence
Logical operators
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&& - logical AND || logical OR ! logical NOT
Assignment
int x = 12; String st = “Hello”; float a = 12.5;
a=b; a+=b; a-=b; a*=b; a/=b; a%=b;
Comparison operators
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==
!=
>
<
>=
<=
Java Statements
if (comparison-op) { code to be exec;}
if (comparison-op)
{do_this_code;} else
{do_this_code_instead;}
switch(num) {
case 1 : {do_this;}
case 2 : {do_that;}
case 3 : {do_the_other;}
Java Statements
for (initial_val; exit_test; increment)
{iterative_code;}
works just like c
while (test_cond) {
do_this_code;}
do {do_this_code;} while (test_cond);
Java - Statements
break; breaks out of a loop
if (x==3) break;
continue; drops through a loop
if (x==3) continue;
labels
bigloop: for…
continue bigloop;
Java Statements
return – returns to the calling method
can return values from called
methods
Java - statements
Arrays
int[] x = {4,5,6};
String[] days = {“Monday”,”Tuesday”,…};