IT151: Introduction to Programming (java)

Transcription

1 IT151: Introduction to Programming (java)

2 Programming Basics Program A set of instructions that a computer uses to do something. Programming / Develop The act of creating or changing a program Programmer / Developer A person who makes a program Run / Execute The act of using a program Every program was created by someone Computers use special languages Programmers use special languages to create or change a program

3 Machine Language High Level Language C++ Java VB.NET Machine Language Hardware Machine language A language understood by computers When programs are run, machine language is used Machine languages are almost impossible for humans to understand Every operating system (OS) has its own machine language Windows Linux Macintosh

4 High Level Languages High Level Language C++ Java VB.NET Machine Language Hardware High Level Language - A programming language that is understandable by people This enables a programmer to write programs High level languages must be translated into machine language before running on a computer

5 Compilers and Interpreters There are two main ways to change programs written in a high level language to machine language: 1. Use a compiler 2. Use an interpreter Source Code Code written in a programming language by a developer.

6 Compilers Compiler A program that transforms code from one format to another High Level Language Machine Language Source code Windows compiler Windows code Windows Linux compiler Linux code Linux Macintosh compiler Macintosh code Macintosh

7 Compilers vs. Interpreters Advantages Programs run faster Disadvantages Platform dependent - Programs only work on a specific operating system. Windows Linux Macintosh Compiling a large program may take a long time

8 Interpreters Interpreter A program that translates and executes code Usually, interpreters translate and execute source code. Machine Language High Level Language Source Code Interpreter Code for Windows, Linux and Macintosh Windows, Linux and Macintosh

9 Interpreters vs. Compilers Advantages Platform Independent. Don t need to compile anything. Disadvantages The interpreter program must be installed on the computer that the program will run on Slower execution You should only use services available on all platforms. Example: Windows has a cool sound library, but you can t use it because it won t run on Macintosh

10 Introduction to Java Java is a programming language created by Sun Microsystems. Java.sun.com Many programmers use Java Java is an object oriented language.

11 Java Setup Steps to install Java Required 1. Install the Java Development Kit (JDK) Find it at Java 2 Standard Edition Not Required but good 1. Install Java Documentation 2. Install Integrated Development Environment (IDE) IDE A program that helps you to write code

12 How Does Java Work? Java uses a compiler and interpreter! You can compile the program once and run it on each platform with an interpreter Source code Java Compiler Java Interpreter Windows Macintosh Windows Linux Byte Code Linux Macintosh

13 How to Create a Java Program 1. Create a source file. 2. Use the Java compiler to create byte code. 3. Run the byte code using the Java interpreter.

14 Create a Source File Write Java source code and save it in a file Use a text editor or Integrated Development Environment (IDE). Filename extension:.java

15 Use the Java Compiler to Create Byte Code Source code is compiled by a Java compiler to byte code. Byte Code A file that can run on any computer that has a Java Interpreter Filename extension:.class Compiler program: javac.exe Source Code Java Compiler void main ()?? this$0?!....java Javac.exe Byte Code.class

16 Use the Java Compiler to Create Byte Code Important Details Javac.exe <filename>.java Ex: Javac HelloWorld.java A.class file is made for every class in the file. Common Errors Unable to find the Compiler - Something is wrong with your Java setup. Windows can t find the Java compiler. Is your access to Javac.exe and Java.exe setup properly? Invalid Flag One of the inputs are wrong. Did you include the.java extension? Are you using the right file?

17 Run the Byte Code Using the Java Interpreter Java Virtual Machine (JVM) A program which interprets Java programs that have been compiled into byte-code and usually stored in a ".class" file. Interpreter performs actions Creates windows Prints Etc. Interpreter program: java.exe Byte Code?? this$0?!....class Java Interpreter Java.exe

18 Run the Byte Code Using the Java Interpreter Important Details Java.exe <class name> Ex: Java HelloWorld The class name must have the correct case! Common Errors NoClassDefFoundError The class can t be found. Is your class in the correct directory? Are you using the correct case?

19 Summary Source Code Extension used for Java source code files Byte code Convert source code into byte code Extension used for Java byte code? Run byte code? Purpose of main() method? Code comments.