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An overview of object-oriented programming (oop) principles and java programming language constructs. It covers the concepts of abstraction and encapsulation, and introduces new java language constructs such as interfaces, generics, and enumerated types. The document also mentions the java collections framework and java swing as examples of class libraries designed using oop principles.
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Introduction to OOP principles
Review language constructs Introduce new language constructs Many from Java 5.
Object-Oriented Programming (OOP)
View software as a collection of objects (entities)
To be discussed later in the semester
Techniques โ Abstraction
Provide high-level model of activity or data
Specify what actions should be performed Hide algorithms
Specify data objects for problem Hide representation
Java Programming Language
Example Interface โ supports procedure abstraction Class โ supports encapsulation
Example Java Collections Framework Java Swing
Java Interface
Collection of Constants Abstract methods Can not be instantiated
Must implement all methods in interface Example class foo implements bar { โฆ } // interface bar
But class can โinheritโ from multiple interfaces
Java Collections Framework
Object that groups multiple elements into one unit Also called container
Interfaces Abstract data type Implementations Reusable data structures Algorithms Reusable functionality
Overview
Introduction to OOP principles
Review language constructs Introduce new language constructs Many from Java 5.
New Java Language Constructs
Iterator interface
Autoboxing & Unboxing
Data value โ Object (of matching class) Data types & classes converted Boolean, Byte, Double, Short, Integer, Long, Float
ArrayList myL = new ArrayList(); myL.add(1); // previously myL.add(new Integer(1)); Integer X = new Integer(2); int y = X; // previously int y = X.intValue();
Also see example in SortValues.java
Enumerated Types
New type of variable with set of fixed values Establishes all possible values by listing them Supports values(), valueOf(), name(), compareTo()โฆ Can add fields and methods to enums Example public enum Color { Black, White } // new enumeration Color myC = Color.Black; for (Color c : Color.values()) System.out.println(c); When to use enums Natural enumerated types โ days of week, phases of the moon, seasons Sets where you know all possible values
Enumerated Types
From "Taming the Tiger" presentation by Joshua Bloch and Neal Gafter at Sun's 2004 Worldwide Java Developer Conference public class Card implements Serializable { public enum Rank { DEUCE, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE, TEN, JACK, QUEEN, KING, ACE } public enum Suit { CLUBS, DIAMONDS, HEARTS, SPADES } private final Rank rank; private final Suit suit; private Card( Rank rank, Suit suit ) { this.rank = rank; this.suit = suit; } public Rank rank( ) { return rank; } public Suit suit( ) { return suit; } public String toString( ) { return rank + " of " + suit; } }
Generics โ Usage
Specify for utility class Automatically performs casts Can check class at compile time
class A { โฆ } class B { โฆ } List myL = new List( ); myL.add(new A( )); // Add an object of type A A a = myL.get(0); // myL element โ class A โฆ B b = (B) myL.get(0); // causes compile time error
Generics โ Issues
Even if class A extends class B List does not extend List
class B { โฆ } class A extends B { โฆ } // A is subtype of B B b = new A(); // A used in place of B List myL = new List(); // compile time error // List used in place of List // List is not subtype of List
Comparable Interface
public int compareTo(Object o) A.compareTo(B) returns Negative if A < B, 0 if A = B, positive if A > B
Imposes total ordering on objects of a class Referred to as the class's natural ordering Can sort using Collections.sort( ) & Arrays.sort( ) Example: Collections.sort(myList); Can use as keys in SortedMap & SortedSet
Comparator Interface
public int compare(Object A, Object B) Negative if A < B, 0 if A = B, positive if A > B
Imposes total ordering on objects of a class Provide alternatives to natural ordering Supports generics Example: class myC implements Comparator{ โฆ } Use as parameter for sort function Example: Collections.sort(myFooList, new myC( ) );
Enhanced For Loop
Has method iterator( ) returns Iterator object
Test hasNext( ), then get & cast next( )
String[ ] roster = {"John", "Mary", "โAlice", "Mark"}; for (String student : roster) System.out.println(student);
Enhanced For Loop
ArrayList roster = new ArrayList( ); roster.add("John"); roster.add("Mary"); Iterator it = roster.iterator( ); // using an iterator while (it.hasNext( )) System.out.println(it.next( )); for (String student : roster) // using for loop System.out.println(student);
Stream Input/Output
A connection carrying a sequence of data (ordered sequence of bytes)
Files, memory, other Strings
Data consisting of characters (e.g., text files) Data consisting of raw bytes (e.g., binary files) Can buffer information
Can define stream with desired characteristics
Using Streams
Connects program to external data Location of stream specified at opening Only need to refer to stream
See fileExamples package
Scanner Class Examples
// old approach to scanning input BufferedReader br = new BufferedReader( new InputStreamReader(System.in)); String name = br.readLine( ); // new approach using scanner Scanner in = new Scanner(System.in); String name = in.nextLine( ); int x = in.nextInt( );
See ScannerExample.java Note use of printf
Annotations Annotation โ Java construct that allow us to add validity constraints to Java Classes Validity constraint example A instance variable cannot assume a negative value A parameter can not be null A method in a class must override a method in its superclass Syntax at-sign (@) followed by annotation type and a parenthesized list of element-value pairs Example @DefaultAnnotationForParameters(NonNull.class) You can ignore annotations in code distribution for class projects
Reviewing Bit-Operations
& and | or ^ exclusive or (xor) ~ complement
and x 11010 y 10110 x & y 10010 or x 11010 y 10110 x | y 11110 xor x 11010 y 10110 x ^ y 01100
BitSet Class
BitSet() โ New bit set BitSet(int nbits) โ Bit set large enough to represent bits with indices from 0 through nbits โ 1 and(BitSet set) โ Performs logical and between the current object and the set parameter (current object is updated with the result) or(BitSet set) โ Performs logical or between the current object and the setparameter (current object is updated with the result) cardinality() โ Returns number of bits set to 1 flip(int bitIndex) โ Sets the bit at the specified index get(int bitIndex) โ Returns true if the bit at bitIndex is set; false otherwise length() โ Index of the highest set bit + 1. It returns zero if the BitSet contains no bits set. size() โ Number of bits space used by the BitSet to represent bit values toString() โ For every bit set, the decimal representation of that index isincluded in the result.
