Java review and more

1. Java review and more

2. Class Header • Public class Welcome • Case sensitive • Body of the class must be enclosed by braces

3. Method Header • Modifier return datatype methodname (datatype parameter) • Public static void main (String [] args) • Public—other classes may invoke method • Static—unique and can be invoked without a subclass • Return value (void) is result or answer—void means method does not return data • Parentheses enclose a list of parameters used by method • Includes data type (string) and identifier (args) • Both class and methods need to have brackets to start and end

4. Importing packages • Some classes and methods are not immediately available and must be imported • Java.applet • Java.awt • Java.io • Java.lang • Java.util

5. Java formatting • \t horizontal tab (8 spaces to the right) • \b backspace (1 space to the left) • \n new line (moves insertion point down 1 line and to the left margin) • \r carriage return (moves insertion point to the left margin)

6. Java primitive data types • Boolean (data stored as one of two states) • Byte stores whole number values in 8-bit (-128 to 127) • Char • Double—numbers up to 14/15 decimal as • Float numbers up to 6/7 decimals • Int whole numbers in 32 bit from -2^31 to 2^31-1 • Long 64 bit whole number values • Short 16 bit whole number values

7. Buffered Reader Constructor • BufferedReader – a class from java.io package • dataIn – identifier variable • = new constructor notation (to construct instance of a class • Buffered Reader () method • InputStreamReader (a bridge from byte streams to character streams) • System.in an object representing the keyboard

8. Conversions • readLine() method –reads input and returns a String containing contents of input • Integer.parseInt(variablename) allows us to convert string to a variable type

9. The if…else Statement • Single: line 29, line 30 • Block: lines 15-26, lines 19-20, lines 23-24 • Nested: lines 17-25, lines 29-30

11. Testing with an if statement • Testing a single condition • if (answer == null) • if (!done) • Testing multiple conditions • if ((gender == “male”) && (age >= 18)) • if ((age < 13) || (age > 65)) • AND and OR expressions evaluate the right operand only if the left operand is not sufficient to decide the condition

12. Exception Handling • An exception is an event resulting from an erroneous situation which disrupts normal program flow • Exception handling is the concept of planning for possible exceptions by directing the program to deal with them gracefully, without terminating • Two kinds of exceptions • Run-time • Checked • The compiler checks each method to ensure each method has a handler

13. Handling Exceptions • The try statement identifies a block of statements that may potentially throw an exception • The throw statement transfers execution from the method that caused the exception to the handler • Transfers execution to the catch statement if the throw is placed within a try statement • The catch statement identifies the type of exception being caught and statements to describe or fix the error • The finally statement is optional and is always executed regardless of whether an exception has taken place • Placed after the catch statement

16. Catch an exception Throw an exception

17. Testing methods • Compile the program after coding each method and call statement • Run the program with correct input • Run the program to test the exception handling with invalid input • Alphabetic data • Negative values • Null or zero values • Verify that the user is allowed to reenter data • Verify the program closes correctly

18. Repetition Structure

19. The getSales() method

20. The getCode() method

21. The Case Structure • A type of selection structure that allows for more than two choices when the condition is evaluated • Used when there are many possible, valid choices for user input • The code evaluates the user choice with a switch statement and looks for a match in each case statement • Each case statement contains a ending break statement which forces exit of the structure

23. Arguments and Parameters • When a method is called, the calling method sends arguments; the called method accepts the values as parameters • Different but related identifier names for the arguments and the parameters should be used for good program design • The variables are only visible in their respective methods • Arguments and parameters for a called method and the calling statement must be of the same number, order, and data type

24. The getComm() Method

25. Formatting Numeric Output • The DecimalFormat class formats decimal numbers into Strings for output • Supports different locales, leading and trailing zeros, prefixes/suffixes, and separators • The argument is a pattern, which determines how the formatted number should be displayed

27. The output() method

28. The finish() method Exits system when program completes successfully

29. Arrays • A method to stores lists of related data items and manipulate data more efficiently • An array can store multiple data items of the same type in a single memory location • Declaring arrays • Int [] ages; • Int ages[]; • Constructing arrays • Ages = new int[100]; • Int [] ages = new int[100];

30. The For Loop • Prior a while loop was used • Good for when you need to perform a task for an undetermined number of times • However, when you want to specify the exact number of times the loop will be executed– use a for • Syntax – for (int j=1; j<5; j++)

31. A simple javascript page • <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> • <!-- Fig. 13.1: welcome.html --> • <HTML> • <HEAD> • <TITLE>A First Program in JavaScript</TITLE> • <SCRIPT LANGUAGE = "JavaScript"> • document.writeln( • "<H1>Welcome to JavaScript Programming!</H1>" ); • </SCRIPT> • </HEAD><BODY></BODY> • </HTML>

32. JavaScript • Extension of java code—except read in browser • Why is javascript better than an applet?

33. How you place it in your web page • <html> • <head> • <script> • Javascript goes here • </script> • </head> • <body> • </body> • You can also make an include call • <script src=“path/to/fileName.js”></script>

34. Making a simple color change • <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> • <HTML> • <!-- Fig. 13.2: welcome.html --> • <HEAD> • <TITLE>Printing a Line with Multiple Statements</TITLE> • <SCRIPT LANGUAGE = "JavaScript"> • document.write( "<FONT COLOR='magenta'><H1>Welcome to " ); • document.writeln( "JavaScript Programming!</H1></FONT>" ); • </SCRIPT> • </HEAD><BODY></BODY> • </HTML>

35. Adding a line break • <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> • <HTML> • <!-- Fig. 13.3: welcome.html --> • <HEAD><TITLE>Printing Multiple Lines</TITLE> • <SCRIPT LANGUAGE = "JavaScript"> • document.writeln( • "<H1>Welcome to<BR>JavaScript<BR>Programming!</H1>" ); • </SCRIPT> • </HEAD><BODY></BODY> • </HTML>

36. Alert/Dialog Box • <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> • <HTML> • <!-- Fig. 13.4: welcome.html --> • <!-- Printing multiple lines in a dialog box --> • <HEAD> • <SCRIPT LANGUAGE = "JavaScript"> • window.alert( "Welcome to\nJavaScript\nProgramming!" ); • </SCRIPT> • </HEAD> • <BODY> • <P>Click Refresh (or Reload) to run this script again.</P> • </BODY> • </HTML>

37. Adding Integers w/Prompt Boxes • <SCRIPT LANGUAGE = "JavaScript"> • var firstNumber, // first string entered by user • secondNumber, // second string entered by user • number1, // first number to add • number2, // second number to add • sum; // sum of number1 and number2 • // read in first number from user as a string • firstNumber = window.prompt( "Enter first integer", "0" ); • // read in second number from user as a string • secondNumber = window.prompt( "Enter second integer", "0" ); • // convert numbers from strings to integers • number1 = parseInt( firstNumber ); • number2 = parseInt( secondNumber ); • // add the numbers • sum = number1 + number2; • // display the results • document.writeln( "<H1>The sum is " + sum + "</H1>" );

38. Comparison Example • <SCRIPT LANGUAGE = "JavaScript"> • var first, // first string entered by user • second; // second string entered by user • // read first number from user as a string • first = window.prompt( "Enter first integer:", "0" ); • // read second number from user as a string • second = window.prompt( "Enter second integer:", "0" ); • document.writeln( "<H1>Comparison Results</H1>" ); • document.writeln( "<TABLE BORDER = '1' WIDTH = '100%'>" ); • if ( first == second ) • document.writeln( "<TR><TD>" + first + " == " + second + • "</TD></TR>" ); • if ( first != second ) • document.writeln( "<TR><TD>" + first + " != " + second + • "</TD></TR>" ); • if ( first < second ) • document.writeln( "<TR><TD>" + first + " < " + second + • "</TD></TR>" ); • if ( first > second ) • document.writeln( "<TR><TD>" + first + " > " + second + • "</TD></TR>" ); • if ( first <= second ) • document.writeln( "<TR><TD>" + first + " <= " + second + • "</TD></TR>" ); • if ( first >= second ) • document.writeln( "<TR><TD>" + first + " >= " + second + • "</TD></TR>" ); • // Display results • document.writeln( "</TABLE>" ); • </SCRIPT>

39. Control Structures • Three main types of selection structure • If • If/Else • Switch • Four types of repetition • While • Do/While • For • For/In

40. The If Selection Structure • Used to choose among alternative courses of action in a program • If a student’s grade is greater than or equal to 60 • Print “Passed” • If ( studentGrade >= 60) • document.writeln( “Passed”);

41. The If/Else Structure • This structure performs an indicated action only when the condition evaluates to true, otherwise the action is skipped, or it can perform a different action if false. • If a student’s grade is greater than or equal to 60 • Print “Passed” • Else • Print “Failed” • If ( studentGrade >= 60) • document.writeln( “Passed”); • Else • document.writeln( “Failed”);

42. Conditional Operator • A special command that functions the same as the If/Else statement • document.writeln( • studentGrade >= 60 ? “Passed” : “Failed” );

43. Nested If/Else Structures • Used to test multiple cases • If student’s grade is greater than or equal to 90 • Print “A” • Else • If student’s grade is greater than or equal to 80 • Print “B” • Else • If student’s grade is greater than or equal to 70 • Print “C” • Else • Print “F”

44. The Compound Else Statement • if (grade >= 60) • document.writeln( “ Passed”); • else { • document.writeln( “Failed <BR>”); • document.writeln(“ You must take this course again”); • }

45. The while repetition structure • A repetition structure allows the programmer to specify an action that is to be repeated while some condition remains true • While there are more items on my shopping list • Purchase next item and cross off my list

46. The while repetition in Javascript • // Initialization Phase • total = 0; // clear total • gradeCounter = 1; // prepare to loop • // Processing Phase • while ( gradeCounter <= 10 ) { // loop 10 times • // prompt for input and read grade from user • grade = window.prompt( "Enter integer grade:", "0" ); • // convert grade from a String to an integer • gradeValue = parseInt( grade ); • // add gradeValue to total • total = total + gradeValue; • // add 1 to gradeCounter • gradeCounter = gradeCounter + 1; • } • // Termination Phase • average = total / 10; // calculate the average • // display average of exam grades • document.writeln( • "<H1>Class average is " + average + "</H1>" );