1. CT1513
Introduction To java
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2. What is Java
Java is a programming language and computing platform first released by Sun Microsystems in 1995. 
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3. Why?
Java is the first programming language to deliberately embrace the concept of writing programs that can be executed on the Web.
The Java language is accompanied by a library of extra software that we can use when developing programs.
The library provides the ability to create graphics, communicate over networks, and interact with databases.
The set of supporting libraries is huge.
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4. Java vs. C++
Both Java and C++ are most popular object-oriented programming languages
C++ was created at AT&T Bell Labs in 1979
Java was born in Sun Microsystems in 1990
The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities.
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5. Java applications and applets
Applications – standalone Java programs
Applets – Java programs that run inside web browsers
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6. Compiling Java Programs
The Java compiler produces bytecode (a “.class” file) not machine code from the source code (the “.java” file).
Bytecode is converted into machine code using a Java Interpreter
Source Code
Bytecode
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7. Platform Independent Java Programs Compiling
You can run bytecode on any computer that has a Java Interpreter installed
“Hello.java”
“Hello.class”
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8. Multipurpose Java Compiling
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9. Running The Program Running The Bytecode (the “.class” file) Class
Loader
Running
Bytecode
Verifier
Bytecode
The Bytecode
(the “.class” file)
Interpreter
JVM
Operating System
Hardware
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10. The Java Virtual Machine Components
The Class Loader
stores bytecodes in memory
Bytecode Verifier
ensures bytecodes do not violate security requirements
Bytecode Interpreter
translates bytecodes into machine language
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11. The Java Virtual Machine
The class Loader, the Bytecode Verifier and Interpreter constitute the Java Virtual Machine (JVM).
JVM is platform specific.
The interpreter translates the bytecodes into specific machine commands.
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12. Java Development Environment
Primary
Memory .
Disk
Editor
Compiler
Class Loader
Program is created in an editor and stored on disk in a file ending with .java.
Compiler creates bytecodes and stores them on disk in a file ending with .class.
Class loader reads .class files containing bytecodes from disk and puts those bytecodes in memory.
Phase 1
Phase 2
Phase 3
Bytecode Verifier
Bytecode verifier confirms that all bytecodes are valid and do not violate Java’s security restrictions.
Phase 4
Interpreter
Interpreter reads bytecodes and translates them into a language that the computer can understand, possibly storing data values as the program executes.
Phase 5
Java Development Environment
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13. Some Characteristics of Java
Object-Oriented
Combines data and behavior into one unit objects
Provides Data abstraction and encapsulation
Decompose program into objects.
Programs are collections of interacting and cooperating objects.
Platform-independent
Portable
”Write-once, run-anywhere”
Secure
The bytecode verifier of the JVM :
checks untrusted bytecode
controls the permissions for high level actions.
Portable- the feature “Write-once-run-anywhere”, also have the standard data size irrespective of operating system or processor.
Dynamic- the user can get the required files from a local drive or from a computer far away from the user, just by connecting with the Internet.
Secure- The security manager, determines the accessibility options of a class like reading and writing a file to the local disk. Java uses the public key encryption system to allow the java applications to transmit over the Internet in the secure encrypted form
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14. Example of Java Programming Code
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