Introduction to Java

1. Introduction to Java IST 311 / MIS 307

2. Java • Three flavors: • Java Standard Edition (Java SE) – client-side standalone application or applets • Java Enterprise Edition (Java EE) – server-side applications like servlets & JavaServer Pages (JSP) • Java Micro Edition (Java ME) – mobile devices like cell phones

3. Java • Java SE 6 – latest version • Java Development Toolkit (JDK) • JDK 1.6 (Java 6 or JDK 6) • Set of programs for developing & testing Java programs from command line • Integrated Development Environment (IDE) • Eclipse for editing, compiling, building, & debugging programs

4. Java • Examples in textbook include line numbers. Feature which may be turned on or off in Eclipse. • Source code • Right click to bring up list • Select Preferences • Click on link to Text Editors • Check mark on Line Numbers • Click OK

5. Objects • An object has structure • Attributes (characteristics) • Behaviors or operations it can carry out (actions)

6. Class Definition • A Java program is written as a class definition • A Java application is a class that contains a main( ) method

7. Class Definition • Import Declaration • Statements to identify the predefined classes used in a Java program • Import declarations must appear before the class declaration • Most Java API’s begin with either “java” (core classes) or “javax” (optional classes) import javax.swing.JOptionPane; import java.io.*;

8. Class Definition • Class Definition has two parts: • Class Header • Class’s name; must be the same name as the .java file • Accessibility as public or private • Pedigree which specifies where it fits in the Java class hierarchy; default is Object class • Class Body • Enclosed within curly brackets { } • Contains instance variables to store data • Contains methods for the actions or behaviors

9. Class Definition • Identifier – name for a class, method, or variable • Must begin with a letter, A to Z, or a to z, an underscore (_), or a dollar sign ($); don’t use $ for your identifiers • May be followed by any number of letters, digits, 0 to 9, an underscore, or dollar sign • May not use a Java keyword (see Appendix A, pg. 709) • Java is case sensitive taxrate vs. TaxRate

10. Class Definition • Data Types – two types in Java • Primitive Data Types (pg.32, Table 2.2) boolean char byte short int long float double • Objects or Reference Variables– programmer created through a class definition • String is an object and therefore a data type

11. Class Definition • Variables – named storage location in memory where a value of a given data type may be stored

12. Start Lab 2

13. Class Definition • Method Definition • Code that carries out a specific task or behavior of the class • Method heading and body • Heading contains • the name • accessibility as public, private, or protected • type of data returned by the method • list of parameters

14. Class Definition • Method Definition • Body contains • Executable statements System.out.print(“Hello.”): • Local variable declarations • Computations or assignment statements sum = num1 + 5; • Calls to other methods • Return statements return sum;

15. Flow of Control: Methods

16. Input from Keyboard • Input is complicated task • Things can go wrong • User types a letter instead of a number • File could be missing • Java has three I/O streams at startup • System.in : refer to standard input device (keyboard) • System.out : refer to standard output device (display) • System.err

17. Input from Keyboard • java.util.Scanner class has a list of methods for data types(pg. 27) • nextByte( ) • nextInt( ) • nextDouble( ) • next( ) • nextLine( ) Scanner input = new Scanner(System.in); double radius = input.nextDouble();

18. Scanner Class • Selects chunks of data from input stream • Stops at the delimiter • Default delimiter = white space • Space, tab, return, newline characters • What happens when type full name in program?

19. Output • In Java, any source or destination for I/O is considered a stream of bytes or characters • To perform output, we insert bytes into the stream • I/O is handled through methods that belong to classes contained in: • java.io package

20. Output • java.io.PrintStream class contains methods • print( ) • println( ) //prints a line feed after data • System.out andSystem.err can be used to write things to the console • System.out.print(“Hello”);

21. Math

22. Assignment Statements • Value are placed into variables using assignment statement • Assignment operator = • Data type of variable on left must be compatible with data type on the right int x = 1; x = 1; x = x + 1;

23. Constants • A constant is a final variable associated with the class rather than with its instances • final – declare a variable that has a value that never changes; must be initialized; named using uppercase by convention public final int EATING = 0;

24. Object Instantiation • Define objects (classes) • To use the object it must be instantiated or invoked • We will do this in the main( ) method • Object instantiation is an example of a reference variable Lab1 x;// reference variable declared x = new Lab1( );//object instantiated x.user_interface( );//method call

25. Naming Conventions • Choose descriptive names with straightforward meanings • First word lowercase and capitalize first letter of subsequent words showInputDialog • Capitalize first letter of class name ComputeArea

26. Proper Indentation & Spacing • Consistent indentation style makes programs clear & easy to read, debug, and maintain int i= 3+4 * 4; inti = 3 + 4 * 4; Bad style Good style

27. Block Style • Next-line style • End-of-line style – Java API standard • Both are acceptable; pick one and stick with it

28. Testing and Debugging • Syntax Errors • Error messages from the compiler • Fatal or Warnings • Run-Time Errors • Cause the program to terminate abnormally • Logic Errors • Mistakes in algorithm used to solve problem

29. Homework 1

30. Numeric Operations

31. Numeric Operations • 4 + 5.0 * 6 • (4 + 5) * 6 • 4 + 5 % 3 • 9 % 2 * 7 / 3

32. Increment & Decrement Operators • When used in isolation, K++ is the same as ++K int k; k = k + 1;

33. Increment & Decrement Operators

34. Shorthand Operators CAUTION: There are no spaces in the shorthand operators.

35. Character Data • Java supports Unicode character set enables characters in a wide variety of languages • ASCII character set is 7-bit code, defines 0 to 127 for the letter, digits, and special characters • First 128 characters of Unicode match ASCII character set, making them backward compatible

36. Character Data • Cast operation such as int to convert one type of data to another type char ch = ‘a’; System.out.println( ch);//displays a System.out.println( (int)’a’);//displays 97

37. Escape Sequences System.out.println(“He said “Jave is fun””); • Syntax error from second quotation character. • Overcome this by using Escape Sequence characters. System.out.println(“He said \“Jave is fun\””); He said “Java is fun”

38. Escape Sequences

39. Format Output • java.text.NumberFormat class • Represent numbers as dollar amounts, percentages, and other formats import java.text.NumberFormat; NumberFormat dollars = NumberFormat.getCurrencyInstance( ); System.out.println(dollars.format(5129.95)); $5,129.95

40. Format Output import java.text.NumberFormat; NumberFormat percent = NumberFormat.getPercentInstance( ); percent.setMaximumFractionDigits(2); System.out.print(percent.format( rate / 100.0);

41. Format Output • java.text.DecimalFormat class • Specify the number of decimal places to display import java.text.DecimalFormat; DecimalFormat threeDigits = new DecimalFormat(“0.000”); System.out.println( threeDigits.format (number));

42. Format Output • print( ) and println( ) cannot directly format certain outputs • Default output of floating-point numbers is typically up to 6 decimal place & 15 decimal places for double • Align output in certain columns • Use printf( ) method

43. Format Output System.out.printf(formatSting, argumentList); • formatString = string specifying the format of the output • argumentList = list of arguments that are constant values, variables, or expressions; multiple arguments separated with commas

44. Format Output

45. Format Output int count = 5 double amount = 45.56 System.out.printf(“count is %d and amount is %f” , count, amount); count is 5 and amount is 45.560000 Pg. 96, Table 3.9 for examples

46. Flow of Control

47. Control Structures • Sequence: one after the other • Selection: selects a path based upon action • Iteration: repetition

48. Selection • Simple if Statement • Nested if / else Multiway Statement • switch Statement • Alternative way to write a multiway selection structure • Involves a test of equality • Logical expression being tested must be a primitive integral type byte, short, int, char, long, or boolean

49. boolean Data Type • Java provides six comparison operators to use when comparing two values

50. boolean Data Type • You can compare characters; however comparison is to ASCII character sets • Equality comparison operator is two equal signs == not a single equal sign used for assignment statement • Result of comparison is a boolean value: true or false