Java review and more

Class Header  Public class Welcome  Case sensitive  Body of the class must be enclosed by braces

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

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

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)

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

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

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

The if…else Statement  Single: line 29, line 30  Block: lines 15-26, lines 19-20, lines  Nested: lines 17-25, lines 29-30

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

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

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

Catch an exception Throw an exception

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

Repetition Structure

The getSales() method

The getCode() method

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

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

The getComm() Method

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

The output() method

The finish() method Exits system when program completes successfully

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];

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++)

A simple javascript page   A First Program in JavaScript   document.writeln(  " Welcome to JavaScript Programming! " ); 

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

How you place it in your web page   Javascript goes here   You can also make an include call 

Making a simple color change   Printing a Line with Multiple Statements   document.write( " Welcome to " );  document.writeln( "JavaScript Programming! " ); 

Adding a line break   Printing Multiple Lines   document.writeln(  " Welcome to JavaScript Programming! " ); 

Alert/Dialog Box   window.alert( "Welcome to\nJavaScript\nProgramming!" );   Click Refresh (or Reload) to run this script again. 

Adding Integers w/Prompt Boxes   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( " The sum is " + sum + " " );

Comparison Example   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( " Comparison Results " );  document.writeln( " " );  if ( first == second )  document.writeln( " " + first + " == " + second +  " " );  if ( first != second )  document.writeln( " " + first + " != " + second +  " " );  if ( first < second )  document.writeln( " " + first + " < " + second +  " " );  if ( first > second )  document.writeln( " " + first + " > " + second +  " " );  if ( first <= second )  document.writeln( " " + first + " <= " + second +  " " );  if ( first >= second )  document.writeln( " " + first + " >= " + second +  " " );  // Display results  document.writeln( " " ); 

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

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”);

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”);

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

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”

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

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

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(  " Class average is " + average + " " );