Strategy Pattern in Java
//[C] 2002 Sun Microsystems, Inc.---
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.text.Collator;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
public class RunStrategyPattern {
public static void main(String[] arguments) {
System.out.println("Example for the Strategy pattern");
System.out.println();
System.out
.println("This code uses two Strategy classes, NameSummarizer and OrganizationSummarizer,");
System.out
.println(" to provide a sorted, summarized list for a ContactList. The ContactList object");
System.out
.println(" maintains a collection of Contacts, and delegates the task of representing");
System.out
.println(" its information to an associated object which implements SummarizingStrategy.");
System.out.println();
System.out
.println("Deserializing stored ContactList from the data.ser file");
System.out.println();
if (!(new File("data.ser").exists())) {
DataCreator.serialize("data.ser");
}
ContactList list = (ContactList) (DataRetriever
.deserializeData("data.ser"));
System.out.println("Creating NameSummarizer for the ContactList");
System.out
.println("(this Strategy displays only the last and first name,");
System.out
.println(" and sorts the list by last name, followed by the first)");
list.setSummarizer(new NameSummarizer());
System.out.println("Name Summarizer Output for the ContactList:");
System.out.println(list.summarize());
System.out.println();
System.out
.println("Creating OrganizationSummarizer for the ContactList");
System.out
.println("(this Strategy displays the organization, followed by the first");
System.out
.println(" and last name. It sorts by the organization, followed by last name)");
list.setSummarizer(new OrganizationSummarizer());
System.out
.println("Organization Summarizer Output for the ContactList:");
System.out.println(list.summarize());
System.out.println();
}
}
interface Contact extends Serializable {
public static final String SPACE = " ";
public String getFirstName();
public String getLastName();
public String getTitle();
public String getOrganization();
public void setFirstName(String newFirstName);
public void setLastName(String newLastName);
public void setTitle(String newTitle);
public void setOrganization(String newOrganization);
}
class ContactImpl implements Contact {
private String firstName;
private String lastName;
private String title;
private String organization;
public ContactImpl() {
}
public ContactImpl(String newFirstName, String newLastName,
String newTitle, String newOrganization) {
firstName = newFirstName;
lastName = newLastName;
title = newTitle;
organization = newOrganization;
}
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public String getTitle() {
return title;
}
public String getOrganization() {
return organization;
}
public void setFirstName(String newFirstName) {
firstName = newFirstName;
}
public void setLastName(String newLastName) {
lastName = newLastName;
}
public void setTitle(String newTitle) {
title = newTitle;
}
public void setOrganization(String newOrganization) {
organization = newOrganization;
}
public String toString() {
return firstName + SPACE + lastName;
}
}
class ContactList implements Serializable {
private ArrayList contacts = new ArrayList();
private SummarizingStrategy summarizer;
public ArrayList getContacts() {
return contacts;
}
public Contact[] getContactsAsArray() {
return (Contact[]) (contacts.toArray(new Contact[1]));
}
public void setSummarizer(SummarizingStrategy newSummarizer) {
summarizer = newSummarizer;
}
public void setContacts(ArrayList newContacts) {
contacts = newContacts;
}
public void addContact(Contact element) {
if (!contacts.contains(element)) {
contacts.add(element);
}
}
public void removeContact(Contact element) {
contacts.remove(element);
}
public String summarize() {
return summarizer.summarize(getContactsAsArray());
}
public String[] makeSummarizedList() {
return summarizer.makeSummarizedList(getContactsAsArray());
}
}
class DataCreator {
private static final String DEFAULT_FILE = "data.ser";
public static void main(String[] args) {
String fileName;
if (args.length == 1) {
fileName = args[0];
} else {
fileName = DEFAULT_FILE;
}
serialize(fileName);
}
public static void serialize(String fileName) {
try {
serializeToFile(makeContactList(), fileName);
} catch (IOException exc) {
exc.printStackTrace();
}
}
private static Serializable makeContactList() {
ContactList list = new ContactList();
list.addContact(new ContactImpl("David", "St. Hubbins", "Lead Guitar",
"The New Originals"));
list.addContact(new ContactImpl("Mick", "Shrimpton", "Drummer",
"The New Originals"));
list.addContact(new ContactImpl("Nigel", "Tufnel", "Lead Guitar",
"The New Originals"));
list.addContact(new ContactImpl("Derek", "Smalls", "Bass",
"The New Originals"));
list.addContact(new ContactImpl("Viv", "Savage", "Keyboards",
"The New Originals"));
list.addContact(new ContactImpl("Nick", "Shrimpton", "CEO",
"Fishy Business, LTD"));
list.addContact(new ContactImpl("Nickolai", "Lobachevski",
"Senior Packer", "Fishy Business, LTD"));
list.addContact(new ContactImpl("Alan", "Robertson", "Comptroller",
"Universal Exports"));
list.addContact(new ContactImpl("William", "Telle", "President",
"Universal Exports"));
list.addContact(new ContactImpl("Harvey", "Manfredjensenden",
"Inspector", "Universal Imports"));
list.addContact(new ContactImpl("Deirdre", "Pine", "Chief Mechanic",
"The Universal Joint"));
list.addContact(new ContactImpl("Martha", "Crump-Pinnett",
"Lead Developer", "Avatar Inc."));
list.addContact(new ContactImpl("Bryan", "Basham", "CTO", "IOVA"));
return list;
}
private static void serializeToFile(Serializable content, String fileName)
throws IOException {
ObjectOutputStream serOut = new ObjectOutputStream(
new FileOutputStream(fileName));
serOut.writeObject(content);
serOut.close();
}
}
class DataRetriever {
public static Object deserializeData(String fileName) {
Object returnValue = null;
try {
File inputFile = new File(fileName);
if (inputFile.exists() && inputFile.isFile()) {
ObjectInputStream readIn = new ObjectInputStream(
new FileInputStream(fileName));
returnValue = readIn.readObject();
readIn.close();
} else {
System.err.println("Unable to locate the file " + fileName);
}
} catch (ClassNotFoundException exc) {
exc.printStackTrace();
} catch (IOException exc) {
exc.printStackTrace();
}
return returnValue;
}
}
class NameSummarizer implements SummarizingStrategy {
private Comparator comparator = new NameComparator();
public String summarize(Contact[] contactList) {
StringBuffer product = new StringBuffer();
Arrays.sort(contactList, comparator);
for (int i = 0; i < contactList.length; i++) {
product.append(contactList[i].getLastName());
product.append(COMMA);
product.append(SPACE);
product.append(contactList[i].getFirstName());
product.append(EOL_STRING);
}
return product.toString();
}
public String[] makeSummarizedList(Contact[] contactList) {
Arrays.sort(contactList, comparator);
String[] product = new String[contactList.length];
for (int i = 0; i < contactList.length; i++) {
product[i] = contactList[i].getLastName() + COMMA + SPACE
+ contactList[i].getFirstName() + EOL_STRING;
}
return product;
}
private class NameComparator implements Comparator {
private Collator textComparator = Collator.getInstance();
public int compare(Object o1, Object o2) {
Contact c1, c2;
if ((o1 instanceof Contact) && (o2 instanceof Contact)) {
c1 = (Contact) o1;
c2 = (Contact) o2;
int compareResult = textComparator.compare(c1.getLastName(), c2
.getLastName());
if (compareResult == 0) {
compareResult = textComparator.compare(c1.getFirstName(),
c2.getFirstName());
}
return compareResult;
} else
return textComparator.compare(o1, o2);
}
public boolean equals(Object o) {
return textComparator.equals(o);
}
}
}
class OrganizationSummarizer implements SummarizingStrategy {
private Comparator comparator = new OrganizationComparator();
public String summarize(Contact[] contactList) {
StringBuffer product = new StringBuffer();
Arrays.sort(contactList, comparator);
for (int i = 0; i < contactList.length; i++) {
product.append(contactList[i].getOrganization());
product.append(DELIMITER);
product.append(SPACE);
product.append(contactList[i].getFirstName());
product.append(SPACE);
product.append(contactList[i].getLastName());
product.append(EOL_STRING);
}
return product.toString();
}
public String[] makeSummarizedList(Contact[] contactList) {
Arrays.sort(contactList, comparator);
String[] product = new String[contactList.length];
for (int i = 0; i < contactList.length; i++) {
product[i] = contactList[i].getOrganization() + DELIMITER + SPACE
+ contactList[i].getFirstName() + SPACE
+ contactList[i].getLastName() + EOL_STRING;
}
return product;
}
private class OrganizationComparator implements Comparator {
private Collator textComparator = Collator.getInstance();
public int compare(Object o1, Object o2) {
Contact c1, c2;
if ((o1 instanceof Contact) && (o2 instanceof Contact)) {
c1 = (Contact) o1;
c2 = (Contact) o2;
int compareResult = textComparator.compare(
c1.getOrganization(), c2.getOrganization());
if (compareResult == 0) {
compareResult = textComparator.compare(c1.getLastName(), c2
.getLastName());
}
return compareResult;
} else
return textComparator.compare(o1, o2);
}
public boolean equals(Object o) {
return textComparator.equals(o);
}
}
}
interface SummarizingStrategy {
public static final String EOL_STRING = System
.getProperty("line.separator");
public static final String DELIMITER = ":";
public static final String COMMA = ",";
public static final String SPACE = " ";
public String summarize(Contact[] contactList);
public String[] makeSummarizedList(Contact[] contactList);
}
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