1. Introduction to Java Dept. Business Computing University of Winnipeg
Yangjun Chen
Dept. Business Computing
University of Winnipeg
11/9/2018

2. Outline: Introduction to Java
What is Java?
- Java characters
A simple Java program
Java download and program execution
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3. What is Java?
Java is a high level programming language that is very similar to C and C ++.
- You do not need to know these languages to learn Java, but they
would help.
Java is an object-oriented language.
Java is platform independent.
Java is multi-threaded.
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4. Java is Object-Oriented
In traditional computer languages, data are separated from
procedures as in C, Pascal, … (procedural language)
Prolog, and (declarative language)
LISP (functional language)
In Java, data are encapsulated by the procedures defined over them.
Traditional languages:
Java:
Data files
procedure1
procedure2
procedureN
data
procedures
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5. Java is Object-Oriented
Advantage of object-oriented programming
- Application independence
- Software reuse
- Easy maintenance of programs
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6. Platform Independence
- A platform is basically some combination of hardware
and software running within a system:
CPU and operating system
- An executable program (object code) may not be executed
on different machines (platforms) due to the fact that each
machine has its own machine instruction set.
Java solves the platform-independence problem by using
bytecodes and the so-called Java Virtual Machine (JVM).
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7. Platform Independence
JVM
- The JVM is some software that implements a virtual or
imaginary machine inside your computer.
- Accordingly, a Java program will be executed in two phases:
compiling and interpreting
The first phase (Java compiler)
- It compiles the program, but instead of generating machine
code specific to hardware, it generates bytecodes.
- Bytecodes are instructions that looks like machine code
but are not specific to any one processor.
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8. Platform Independence
The second phase (Java interpreter)
- The interpreter will read in the bytecode and translate it
into native machine instructions.
- The Java bytecode interpreter is often called the Java
Virtual machine or the Java Runtime.
By the traditional language, a program is compiled into
machine code or processor instructions.
- These instructions are specific to the processor your
computer is running.
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9. Platform Independence
Java:
Traditional compiler:
Java code
code
Java
Compiler
compiling
SPARC
compiler
Power
compiler
Pentium
compiler
compiling
Java Bytecode
interpreting
SPARC
Power PC
Pentium
SPARC
Power PC
Pentium
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10. Java Virtual Machine
The JVM is different for each platform because each machine
has a different machine instruction set.
- But all JVMs take Java bytecode as input.
Interpreters are slower than compilers because they translate
as they go.
Using the “Just-In-Time” compiler, Java increases the execution
speed which rivals that of C++.
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11. Java is Multi-Threaded
Multithreading can be loosely defined as the simultaneous
execution of multiple processes within a program.
Java is inherently multi-threaded.
- For example, multiple applets can run on the same web page with
each applet receiving more or less equal CPU time.
Downside to multi-threading
- Errors in using threads can be very difficult to locate.
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12. A simple Java Program Let’s take a look at a simple program
import java.lang.*;
//A simple Java application
public class HelloWorld {
public static void main(String args[]) {
System.out.println(“HelloWorld!”); }
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13. Java Download and Program Execution
Java Download (JDK1.1.8) -
(you’ll see a table.)
In the first item of the table, click “continue” button.
(you’ll see the license information.)
click “ACCEPT” button
jdk-1_1_8_004-win.exe will be stored in your computer.
- PATH and CLASSPATH setting (Windows 95/98)
Example: (in Autoexec.bat file)
PATH C:\Novell\Client32;%PATH%;C:\jdk1.1.8\bin
set CLASSPATH=.;jdk1.1.8\bin\..\classes;jdk1.1.8\lib\classes.zip
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14. Java Download and Program Execution
Java Download (JDK1.4) -
(you’ll see J2SE SDK
Click on this, you’ll get another page for downloading
Click on “download”
You’ll see a table with title “Dowload J2SE v 1.4.2_03”
Click on “download” under “SDK”
(you’ll see the license information)
click “ACCEPT” button.
In the next page, click on
Windows Offline Installation, Multi-language
(j2sdk-1_4_2_03-windows-i586-p.exe, MB)
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15. Change path environment variable: For windows 2000,
My Computer  Control  panel System
click on Tab “Advanced”
click on “Environment Variables …”
edit the system variable “Path” by adding
;C:\J2SDK-1_4_2_03\bin
RealJ Download
Using Google or Yahoo to find ‘RealJ’ home page;
and then download it onto your computer.
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16. Java Download and Program Execution
- The code should be written in a plain text editor; not a word processor.
The file name must be of the form: <filename>.java; <filename> must
match the public class name stored in it.
Example: HelloWorld.java
- You would then compile the program using “javac”, the Java compiler.
Example: javac HelloWorld.java
- A class, for example, HelloWorld.class, will be produced.
- The final step is to run the program:
java HelloWorld
This will print “HelloWorld!” onto the screen.
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17. What is the difference between the object-oriented method
and the traditional programming method with files?
What is the platform-independence?
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