CSE 1030: Implementing Mixing static and non-static features Mark Shtern

Summary Class this parameter Memory Standard methods compareTo toString, equals, hashCode compareTo

Ex10 Design and implement a Rectangle class Attributes Width Height Methods getArea Assessors, Mutators Write application that sorts Rectangles by area

Find a Bug import java.util.*; public class Name { private final String first, last; public Name(String first, String last) { this.first = first; this.last = last; } public boolean equals(Object o) { if (!(o instanceof Name)) return false; Name n = (Name)o; return n.first.equals(first) && n.last.equals(last); public static void main(String[] args) { Set<Name> s = new HashSet<Name>(); s.add(new Name("Mickey", "Mouse")); System.out.println (s.contains(new Name("Mickey", "Mouse"))); }

Avoiding code duplication Constructor Chaining Delegation to Mutators Delegation to Accessors

Attribute Attribute selection Attribute Caching Money  Cents Polynomial  Coefficients Attribute Caching

Summary Objects Utility Class

Utility vs Class State full static this Constructors Methods State less

Utility vs Class Utility Object/Class State less or shared state static No public constructors All static methods Invocation: ClassName.methodName() Object/Class State Public constructors Instance variables/ Attributes Instance Reference variable/this Invocation: objectName.methodName() Instantiation: obj Name= new ClassName(...)

Standard Methods (Object) toString()  returns a string that represents the current object equals()  indicates whether some other object is "equal to" this one hashCode()  returns an integer (hash code value) for the object. This method is supported for the benefit of containers

V Hash Code Examples Object Hash Code Point p1 = new Point(); 1 12 Object Hash Code Point p1 = new Point(); 1 Point p2 = new Point(); V

V V Hash Code Examples Object Hash Code Point p1 = new Point(1,2); 1 12 V Object Hash Code Point p1 = new Point(1,2); 1 Point p2 = new Point(1,1); V

Immutable Objects It is an object whose state cannot be modified after it is created. String, Double, Integer No public mutators

Features Static Feature Non-static Feature Mixing Static and Non-Static Feature

Incorporating an Invocation Counter Refractor the Rectangle class to keep track of the number of times the getArea method is used

Stamping a Serial Number on Objects Design a patter that helps to associate unique serial number with every instance of a class Apply the pattern for Rectangle class. Every rectangle should have a unique serial number that starts at 1 and increments serially.

Singleton Pattern Singleton pattern is restricting the instantiation of a class to one object Singleton pattern is a design pattern public static ClassName getInstance(); private static ClassName instance = new ClassName(..);