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 23-24 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 < 13) || (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() methodExits 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 <!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>

JavaScript Extension of java code—except read in

browser Why is javascript better than an applet?

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>

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>

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>

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>

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>" );

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>

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 <BR>”); 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( "<H1>Class average is " + average + "</H1>" );