Chapter 2 Getting Started with Java Part B

Topics Components of a Java Program –classes –methods –comments –import statements Declaring and creating objects –Java identifiers Standard Java classes Development Example

Warm-up Exercises First homework assignment (on the web) –Chapter 1 problems 2, 4, 5 –Chapter 2 problems 1, 9 (parts a, c, g, j), 12 Practice –Chapter 1 # 3: CD class –Chapter 1 # 14: Inheritance hierarchy for contact manager (Person, Professional contact, Friend, Student)

UML Class Diagrams An example of a UML diagram for the CD class Diagram has only instance data and methods Class data and methods would be underlined

Inheritance Hierarchy

Template for Java Program

Edit-Compile-Run Cycle Edit vi MyClass.java Compile javac MyClass.java Run java MyClass

Java Standard Classes Java comes with an extensive set of classes that you can use. Using existing Java classes is an important step in becoming a successful and proficient programmer. The standard classes are organized into packages

Standard Classes We will introduce four standard classes here: –String –JOptionPane –Date –SimpleDateFormat

String A string is basically some text –a sequence of characters We've seen String objects in our programs already –"this is a String" –These are constant or literal String objects –They have no name –They can't be changed String class is in java.lang (no import statement required)

Creating Strings Putting a literal string in your program creates a String automatically You can declare a String object and assign it to the literal String String fixedString = "some text"; -the String class is the only one you can do this with You can use new to create a new String from an existing one –String newString = new String( "more text"); –String newString2 = new String( newString);

String Methods The String class has many methods We'll look at a few –length() returns the number of characters in the String String text = "Espresso"; text.length() returns 8 –String concat( String toAdd) creates a new String out of the original String followed by the argument String Can use + as a shortcut for this method (another unique property of the String class) "acro" + "bat" is "acrobat"

indexOf method The indexOf method can be used to locate one String in another –indexOf( String toFind) returns the position of toFind in the String –Positions are numbered starting from 0 –the index of "press" in "Espresso" is 2 –if the toFind String isn't present, the result is -1

substring method substring returns a new String which is part of a larger String –substring( start, justAfter) start is the desired starting index justAfter is the index of the first character past the desired substring

Using the substring method

Special Characters What if you need a string that has several lines of text in it? You can't spread a literal string over multiple lines You need to put a character into the string that represents a carriage return –"\n" is a special character that represents a newline the \ is an escape character that tells the compiler to interpret the next character differently from its usual meaning We'll see other special characters that start with a \

GUI Windows Windows come in 2 forms in a GUI interface 1.application windows which are generally long-lived JFrame objects in Java 2.dialog boxes are short-lived JDialog objects in Java allow the user to interact with the program come in many forms - the JDialog class has to be quite complex to support this variety some common forms –messages –confirmation (yes/no/cancel) –input

JOptionPane Allows you to easily create common types of JDialog objects All methods are class methods – you never create a JOptionPane object –call the methods using JOptionPane.methodName() JOptionPane is in the javax.swing package

Message Dialogs Used when you need to be sure the user has been informed about something –results –error messages and warnings JOptionPane.showMessageDialog( parent, message) –parent is the name of the JFrame the JDialog is attached to (or null if it is not attached to a JFrame) –message is the text to be displayed (a String)

Input Dialogs Another common form of dialog is one used to ask for a small amount of input JOptionPane.showInputDialog( String prompt) –displays a box for the user to enter something – returns the String that the user types in

Using Dates in Java The Date class in Java represents time to the nearest millisecond Create a Date with the current time using Date today = new Date(); The toString method of the Date class returns a String representing the complete time and date Weekday Month day hours:minutes:seconds timezone year Date is in java.util

Other Date Formats Use the SimpleDateFormat class Create a SimpleDateFormat object with a "picture" of what you want it to look like –picture is a string with codes for the various fields SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy"); SimpleDateFormat is in the java.text package

SimpleDateFormat Codes Yyearnumberyyyy->2004 Mmonthtext or number MM->10 MMM-> Oct dday in monthnumberdd->20 hhour in (am/pm)numberhh->09 aam/pmtexta->am mminutes in hournumbermm->35 sseconds in minutenumberss->54 Eday in weektextE-> Sat.

Software Lifecycle The sequence of stages from conception to operation of a program is called software life cycle. Five stages are –Analysis –Design –Coding –Testing –Operation and Maintenance

Sample Development: Printing Initials Problem statement: Write an application that asks for the user’s first, middle, and last names and replies with their initials. Overall plan: –Get the user’s first, middle, and last names. –Extract the initials to form the monogram. –Output the monogram.

What classes do we need?

Necessary classes Name, initials and monogram need String Need JOptionPane for input and output –To input the name, we need an input dialog –To output the monogram, we need a message dialog

UML Diagram for Ch2Monogram

Phase 1 Input the user's name –first middle last Choices –one dialog for each part easy to program tedious for user –single dialog for the entire name harder to program need to specify format in this case nicer for user

Phase 2 Compute and display monogram –need to display result to know whether computation is correct How to separate name into 3 parts? –use indexOf to find space –use substring to separate at space –repeat for second space How to get initial from each part? –substring(0,1)