Computer Programming 12 Mr. Jean March 19 th, 2013.
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Transcript of Computer Programming 12 Mr. Jean March 19 th, 2013.
2.1 Why Java?
• Java is the fastest growing programming language in the world.
• Java is a modern object-oriented programming language.
• Java has benefited by learning from the less desirable features of early object-oriented programming languages.
2.1 Why Java?
• Java is ideally suited to develop distributed, network-based applications because it:
– Enables the construction of virus-free, tamper-free systems (security)
– Supports the development of programs that do not overwrite memory (robust)
– Yields programs that can be run on different types of computers without change (portable)
2.1 Why Java?
• Java supports advanced programming concepts such as threads.
– A thread is a process that can run concurrently with other processes.
• Java resembles C++, the world’s most popular industrial strength programming language.
• Java however, runs more slowly than most modern programming languages because it is interpreted.
2.2 The Java Virtual Machine and Byte Code
• Java compilers translate Java into pseudomachine language called java byte code.
• To run java byte code on a particular computer, a Java virtual machine (JVM) must be installed.
2.2 The Java Virtual Machine and Byte Code
• A Java virtual machine is a program that acts like a computer. It is called an interpreter.
• Disadvantage:– Runs more slowly than an actual
computer• To combat slower processing, some JVMs
translate code when first encountered. This is known as just-in-time compilation (JIT).
2.2 The Java Virtual Machine and Byte Code
• Advantages:
– Portability. Any computer can run Java byte code.
– Applets. Applets are small Java programs already translated into byte code.
• Applets run in a JVM incorporated in a web browser• Applets can be decorative (like animated characters on
a web page.)• Applets can be practical (like continuous streams of
stock market quotes.)
– Security. It is possible to limit the capabilities of a Java program since it runs inside a virtual machine.
2.3 Choosing a User Interface Style
• There are two types of user interfaces available to use to create Java programs.
– Graphical User Interface (GUI)– Terminal I/O interface
• Figure 2-1 illustrates both interfaces used to create the same program.
2.3 Choosing a User Interface Style
• There are 3 reasons for beginning with terminal I/O:
– It is easier to implement than a GUI– There are programming situations that
require terminal I/O– Terminal-oriented programs are similar in
structure to programs that process files of sequentially organized data. (What is learned here is easily transferred to that setting.)
2.4 Hello World
• A program is a sequence of instructions for a computer.
• The following is the bulk of instructions, or source code, for the “hello world” program.
2.4 Hello World
• Sending messages to objects always takes the following form:
<name of object>.<name of message>(<parameters>)
2.4 Hello World
• The original “hello world” program needs to be embedded in a larger framework defined by several additional lines of code, in order to be a valid program.
2.5 Edit, Compile, and Execute
• Development environments:– Unix
• standard text editor• command line activation of compiler and JVM
– DOS, using Microsoft Windows and NT OS• notepad text editor• command line activation of compiler and JVM
from a DOS window– Integrated development environment, using
Windows, NT, or MAC OS• Examples: Symantec’s Visual Café, Microsoft’s
Visual J++, or Borland’s J Builder
2.5 Edit, Compile, and Execute
• Preparing your development environment:
– Create a directory, open a terminal window, use the cd command to move to your new directory
– Open notepad, create the file HelloWorld.java, type in the lines of code
– Save the file, go back to the terminal window, compile the program
– Run the program
2.5 Edit, Compile, and Execute
• The following figures illustrate the steps necessary for preparing your development environment.
Today’s Task:
• Create a program which completes the following task.
• Output Display needed:
a = 30b = 40a * b = 1200
Today’s Task:
• Build Program #2
• Build Program #3
• Using what we have seen in programs #2 & #3, build a program which successfully asks for your name, what class your are in and today’s date.