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Introduction to Computers and Java

Introduction to Computers and Java. Chapter 1.3. A Sip of Java: Outline. History of the Java Language Applets A First Java Program Compiling a Java Program or Class Running a Java Program Objects and Methods A Sample Graphics Applet. History of Java.

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Introduction to Computers and Java

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  1. Introduction to Computers and Java Chapter 1.3

  2. A Sip of Java: Outline • History of the Java Language • Applets • A First Java Program • Compiling a Java Program or Class • Running a Java Program • Objects and Methods • A Sample Graphics Applet

  3. History of Java • In 1991, James Gosling and Sun Microsystems began designing a language for home appliances. • In 1994, Gosling realized that his language would be ideal for a Web browser that could run programs over the Internet.

  4. History of Java, cont. • Programs were translated first into an intermediate languagecommon to all appliance processors. • Then the intermediate language was translated into the machine language for a particular appliance’s processor.

  5. Two Kinds of Java Program • applications • meant to be run on your computer • applets • meant to be sent to another location on the Internet and run there

  6. Creating a Java Program or Java Class • A Java program consists of one or more classes, which must be compiled before running the program. • Each class should be in a separate file. • The name of the file should be the same as the name of the class.

  7. Hello World public class HelloWorld { public static void main(String[ ] args) { System.out.println("Hello World!"); } } • In what file should we store this program?

  8. A First Java Application • class FirstProgram

  9. Printing to the Screen System.out.println (“Whatever you want to print”); • System.outis an object for sending output to the screen. • printlnis a method to print whatever is in parentheses to the screen.

  10. Compiling and Running • We will simply use a text editor and a command-line program. • When a Java program is compiled, the byte-code version of the program has the same name, but the ending is changed from.javato .class.

  11. Errors three kinds or errors • syntax errors • runtime errors • logic errors

  12. Syntax Errors • grammatical mistakes in a program • The compiler catches syntax errors and prints an error message. • example: using a period where a program expects a comma

  13. Runtime Errors • errors that are detected when your program is running, but not during compilation • When the computer detects an error, it terminates the program an prints an error message. • example: attempting to divide by 0

  14. Logic Errors • errors that are not detected during compilation or while running, but which cause the program to produce incorrect results • example: an attempt to calculate a Fahrenheit temperature from a Celsius temperature by multiplying by 9/5 and adding 23 instead of 32

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