boolean add(object o) Method Description (from docs API ) Method Description (from docs API )

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1 Interface Collection Method Description (from docs API ) boolean add(object o) boolean addall(collection c) void clear() ensures that this collection contains the specified element adds all of the elements in the specified collection to this collection removes all of the elements from this collection Containers - Part 1 Suggested Reading: Bruce Eckel, Thinking in Java (Fourth Edition) Holding Your Objects (Collection, Iterator,ArrayList) boolean contains(object o) boolean containsall(collection o) boolean equals(object o) returns true if this collection contains the specified element returns true if this collection contains all of the elements in the specified collection compares the specified object with this collection for equality 2 Interface Collection Interface Collection Method Description (from docs API ) Method Description (from docs API ) int hashcode() returns the hash code value for this collection boolean isempty() returns true if this collection contains no elements int size() returns the number of elements in this collection Iterator iterator() boolean remove(object o) boolean removeall(collection c) returns an iterator over the elements in this collection removes a single instance of the specified element from this collection, if it is present removes all of this collection's elements that are also contained in the specified collection Object[] toarray() Object[] toarray(object[] a) returns an array containing all of the elements in this collection returns an array containing all of the elements in this collection boolean retainall(collection c) retains only the elements in this collection that are contained in the specified collection import java.util.*; 3 4

2 Class ArrayList Constructor Description (from docs API ) ArrayList() constructs an empty list with an initial capacity of ten ArrayList(Collection c) constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator ArrayList(int initialcapacity) constructs an empty list with the specified initial capacity

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5 Do not forget to override equals and tostring!!! Towards Collection - equals(object o) Towards Collection - equals(object o) 19 20

6 Fetching containers (a) A simplified view on ArrayList Interface List Fetching (ArrayList) containers (b) Method Description (from docs API ) Object get(int index) returns the element at the specified position in this list Object replaces the element at the specified position in this set(int index, Object element) list with the specified element int lastindexof(object o) boolean remove(object o) returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element removes the first occurrence of the specified element from this list, if it is present 23 24

7 Fetching containers (c) Interface Iterator Interface Collection Method Description (from docs API ) Method Description (from docs API ) boolean hasnext() returns true if the iteration has more elements... Object next() returns the next element in the iteration Iterator iterator() returns an iterator over the elements in this collection... void remove() removes from the underlying collection the last element returned by this iterator Fetching containers (c) Fetching containers (c) Iterator it; X it = new Iterator(); import java.util.iterator; 27 28

8 X A problem... Another (annoying) problem... Perform a cast Generics and type-safe containers Generics and type-safe containers Compilation Error!!! 31 32

9 Generics and type-safe containers Generics and type-safe containers Runtime Error!!! Compilation Error!!! Replace Constructors with Creation Methods Loan +Loan(commitment, riskrating, maturity) +Loan(commitment, riskrating, maturity, expiry) +Loan(commitment, outstanding, riskrating, maturity, expiry) +Loan(capitalStrategy, commitment, riskrating, maturity, expiry) +Loan(capitalStrategy, commitment, outstanding, riskrating, maturity, expiry) Companion Slides

10 Replace Constructors with Creation Methods Replace Constructors with Creation Methods Loan -Loan(capitalStrategy, commitment, outstanding, riskrating, maturity, expiry) +createtermloan(commitment, riskrating, maturity) : Loan!!! communicates what kinds of instances are available better than constructors bypasses constructor limitations makes it easier to find unused creation code +createtermloan(capitalstrategy, commitment, riskrating, maturity, expiry) : Loan +createrevolver(commitment, outstanding, riskrating, expiry) : Loan +createrevolver(capitalstrategy, commitment, outstanding, riskrating, expiry) : Loan +createrctl(commitment, outstanding, riskrating, maturity, expiry) : Loan +createrctl(capitalstrategy, commitment, outstanding, riskrating, maturity, expiry) : Loan " makes creation nonstandard Compose Method Compose Method private void paintcard(graphics g) { Image image = null; if(card.gettype().equals( Problem )) image = explanations.getgameui().problem; else if if(card.gettype().equals( Solution )) image = explanations.getgameui().solution; g.drawimage(image,0,0, explanations.getgameui()); private void paintcard(graphics g) { printcardimage(g); if(shouldhighlight()) paintcardhighlight(); paintcardtext(g); if(shouldhighlight()) paintcardhighlight(); paintcardtext(g);

11 Compose Method Compose Method - another example!! " " efficiently communicates what/how a method does simplifies a method by breaking it up can lead to an overabundance of small methods can hamper debugging public void add(object element) { if (!readonly) { int newsize = size + 1; if (newsize > elements.length) { Object[] newelements = new Object[elements.length + 10]; for (int i=0; i < size; i++) newelements[i] = elements[i]; elements = newelements; elements[size++] = element; Compose Method - another example Compose Method - another example public void add(object element) { if (readonly) return; int newsize = size + 1; if (newsize > elements.length) { Object[] newelements = new Object[elements.length + 10]; for (int i=0; i < size; i++) newelements[i] = elements[i]; elements = newelements; elements[size++] = element; public void add(object element) { if (readonly) return; int newsize = size + 1; if (newsize > elements.length) { Object[] newelements = new Object[elements.length + GROWTH_INCREMENT]; for (int i=0; i < size; i++) newelements[i] = elements[i]; elements = newelements; elements[size++] = element;

12 Compose Method - another example Compose Method - another example public void add(object element) { if (readonly) return; if (atcapacity()) { Object[] newelements = new Object[elements.length + GROWTH_INCREMENT]; for (int i=0; i < size; i++) newelements[i] = elements[i]; public void add(object element) { if (readonly) return; if (atcapacity()) grow(); elements = newelements; elements[size++] = element; elements[size++] = element; Compose Method - another example ProductFinder... public List bycolor(color colorofproducttofind)... public void add(object element) { if (readonly) return; if (atcapacity()) grow(); public List byprice(float pricelimit)... public List bysize(int sizetofind)... public List belowprice(float price)... public List belowpriceavoidingacolor(float price, Color color)... public bycolorandbelowprice(color color, float price)... public bycolorsizeandbelowprice(color color, int size, float price)... addelement(element);

13 public List bycolor(color colorofproducttofind) { public class ProductFinder { private ProductRepository repository; public ProductFinder(ProductRepository repository) { this.repository = repository; List foundproducts = new ArrayList(); Iterator products = repository.iterator(); while (products.hasnext()) { Product product = (Product) products.next(); if (product.getcolor().equals(colorofproducttofind)) foundproducts.add(product); return foundproducts; public List byprice(float pricelimit) { List foundproducts = new ArrayList(); Iterator products = repository.iterator(); while (products.hasnext()) { Product product = (Product) products.next(); if (product.getprice() == pricelimit) foundproducts.add(product); return foundproducts; public class ColorSpec { private Color colorofproducttofind; public ColorSpec(Color colorofproducttofind) { this.colorofproducttofind = colorofproducttofind; public Color getcolorofproducttofind() { return colorofproducttofind;

14 public List bycolor(color colorofproducttofind) { ColorSpec spec = new ColorSpec(colorOfProductToFind); List foundproducts = new ArrayList(); Iterator products = repository.iterator(); while (products.hasnext()) { Product product = (Product) products.next(); if (product.getcolor().equals(spec.getcolorofproducttofind())) foundproducts.add(product); return foundproducts; public List bycolor(color colorofproducttofind) { ColorSpec spec = new ColorSpec(colorOfProductToFind); List foundproducts = new ArrayList(); Iterator products = repository.iterator(); while (products.hasnext()) { Product product = (Product) products.next(); if (issatisfiedby(spec, product)) foundproducts.add(product); return foundproducts; private boolean issatisfiedby(colorspec spec, Product product) { return product.getcolor().equals(spec.getcolorofproducttofind()); public List bycolor(color colorofproducttofind) { ColorSpec spec = new ColorSpec(colorOfProductToFind); List foundproducts = new ArrayList(); Iterator products = repository.iterator(); while (products.hasnext()) { Product product = (Product) products.next(); if (spec.issatisfiedby(product)) foundproducts.add(product); public abstract class Spec { public abstract boolean issatisfiedby(product product); public abstract class ColorSpec extends Spec {... return foundproducts;

15 public class BelowPriceSpec extends Spec{ public List bycolorandbelowprice(color color, float price) { List foundproducts = new ArrayList(); Iterator products = repository.iterator(); while (products.hasnext()) { Product product = (Product) products.next(); if (product.getprice() < price && product.getcolor().equals(color)) foundproducts.add(product); return foundproducts; private float pricethreshold; public BelowPriceSpec(float pricethreshold) { this. pricethreshold = pricethreshold; public float issatisfiedby(product product) { return product.getprice() < getpricethreshold(); public float getpricethreshold() { return pricethreshold(); public List bycolorandbelowprice(color color, float price) { ColorSpec colorspec = new ColorSpec(color); BelowPriceSpec pricespec = new BelowPriceSpec(price); List foundproducts = new ArrayList(); Iterator products = repository.iterator(); while (products.hasnext()) { class AndSpec extends Spec { private Spec first, second; public AndSpec(Spec first, Spec second) { this.first = first; this.second = second; Product product = (Product) products.next(); if (colorspec.issatisfiedby(product) && pricespec.issatisfiedby(product)) foundproducts.add(product); public boolean issatisfiedby(product product) { return first.issatisfiedby(product) && second.issatisfiedby(product); return foundproducts;

16 AndSpec = new AndSpec(new BelowPriceSpec(price), new NotSpec(new ColorSpec(color))); AndSpec = new AndSpec(new BelowPriceSpec(price), new NotSpec(new ColorSpec(color))); public List selectby(spec spec) { List foundproducts = new ArrayList(); Iterator products = repository.iterator(); while (products.hasnext()) { Product product = (Product) products.next(); if (spec.issatisfiedby(product)) foundproducts.add(product); return foundproducts;