Health Informatics CS7014 Introduction to programming

1
Health Informatics CS7014Introduction to
programming

• Lecture Week 4
• 31st October 2008
• Ivana Dusparic
• Ivana.Dusparic-at-cs.tcd.ie

2
Review

• Class
• Instance of a Class
• Instance variables
• Constants
• Methods
• Local variables
• Passing parameters
• Returning values

3
Lecture Overview

• Constructors
• Java String class

4
Constructor methods

• Constructors are special methods in the class
  having the same name as the class that are used
  to create an instance of that class.
• We can use a Constructor to initialise the
  instances instance variables.
• Constructors have no return type, not even void
• We can also write other Constructor methods which
  have parameters.
• The Constructor method is invoked when the
  instance is created. e.g. new Rectangle()

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Example Rectangle Constructors

• class Rectangle
• //instance variables
• int width
• int height
• // Default Constructor
• Rectangle()
• width 5
• height 5
• //Another Constructor method with parameters
• Rectangle(int w, int h)
• width w
• height h

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Using the constructor

• public static void main(String args)
• Rectangle rect1 new Rectangle()
• Rectangle rect2 new Rectangle(10,15)
• Console.println(Area rect1.getArea())
• Console.println(Area rect2.getArea())

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Default Constructor

• Constructor which takes no arguments
• If you do not implement any constructors in your
  class, java will provide default one for you
• e.g. We used Rectangle r new Rectangle()
  without implementing Rectangle() constructor
• If you implement any constructors yourself, Java
  will not provide default one

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The Java String class

• The Java language is accompanied with a standard
  set of classes that can be used by any java
  program.
• These classes provide basic programming
  functionality e.g. String, Math, File,
  FileReader.
• String is a very useful class used to store and
  manipulate text.
• The String class has an instance variable which
  is a list of type char to store the text.
• It has many methods for manipulating the text.

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Example Attribute of type String

• class Rectangle
• //instance variables
• int width
• int height
• String colour
• // Default Constructor
• Rectangle()
• width 5
• height 5
• colour blue
• //Another Constructor method with parameters
• Rectangle(int w, int h, String c)
• width w
• height h
• colour c

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String class

• Classes are logically grouped into Java packages
• e.g. java.lang, java.io
• The java.lang package provides fundamental
  classes for programming in Java.
• The String class is part of this package
• full class name is java.lang.String
• but we can just use String
• You can view documentation on all standard java
  packages here -http//java.sun.com/j2se/1.5.0/docs
  /api/

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String class documentation

• In order to know how to use a classs methods we
  must look at its documentation.
• To use a method, we just need to know the name of
  the method, its input parameters and its return
  value if any.
• Go to the javadoc for the java packages and in
  the left top frame browse to the java.lang
  package and then in the left lower frame to the
  String class.
• The documentation lists each of the classs
• data attributes (Fields)
• constructor methods
• normal methods

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Some example methods

• some of the methods of the String class
• int length()
• String toUpperCase()
• String toLowerCase()
• String substring(int beginIndex) //starts at 0
• String substring(int beginIndex, int endIndex)
• char charAt(int index)
• boolean equals(Object anotherObject)
• boolean endsWith(String suffix)
• boolean startsWith(String prefix)
• String trim()
• int indexOf(int ch)
• int indexOf(String str)
• String replace(char oldChar, char newChar)

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Example things we can do using String methods

• Count number of words in a sentence
• Count number of times a given character occurs in
  a sentence
• Reverse words in a sentence
• Reverse words
• Ideas how to do these using methods provided?

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Todays Lab

• Methods with parameters
• Constructors
• String methods