디자인 패턴은 복잡한 문제에 대한 솔루션입니다. 디자인 패턴은 특정 디자인 문제를 해결하는 방식으로 클래스와 인터페이스를 만드는 것입니다. 일반적으로 시스템을 설계하는 동안 몇 가지 문제가 발생하며 이러한 문제에 대한 일련의 설계 패턴이 있습니다. 디자인 패턴은 일반적으로 클래스, 인터페이스 및 해당 클래스 간의 관계를 포함하는 템플릿입니다.
이러한 유형의 패턴은 주어진 상황에 맞게 객체 생성을 처리합니다.
생성 수준에서는 시스템의 특정 부분을 독립적으로 생성하거나 함께 구성하여 유연성과 호환성을 보장하는 방법을 결정할 수 있습니다.
이 카테고리에 속하는 디자인 패턴 목록은 다음과 같습니다.
싱글턴 디자인 패턴의 필수 요소:
싱글턴 디자인 패턴 예시
public class Singleton {
// Private static instance of the class
private static Singleton instance;
private int count;
// Private constructor to prevent instantiation
private Singleton() {
// initialization code
}
// Public static method to provide access to the instance
public static synchronized Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
// Example method
public void getCount() {
System.out.println("The value of count is: " + count);
}
public void increaseCount() {
count++;
}
public void decreaseCount() {
count--;
}
}
public class Main {
public static void main(String[] args) {
// Get the single instance of Singleton
Singleton singleton = Singleton.getInstance();
singleton.increaseCount();
singleton.getCount(); // Output: The value of count is: 1
// Get the same instance of Singleton
Singleton anotherSingleton = Singleton.getInstance();
anotherSingleton.decreaseCount();
anotherSingleton.getCount(); // Output: The value of count is: 0
// Both singleton and anotherSingleton refer to the same instance
}
}
빌더 패턴의 주요 필수 사항:
빌더 패턴의 예:
이 예에서는 빌더 디자인 패턴을 사용하여 단계별로 재료를 추가하여 초콜릿 스프레드 빵을 만드는 방법을 보여줍니다.
// Product Class
class Bread {
private String bread;
private String spread;
private String chiaSeeds;
private String pumpkinSeeds;
public void setBread(String bread) {
this.bread = bread;
}
public void setSpread(String spread) {
this.spread = spread;
}
public void setChiaSeeds(String chiaSeeds) {
this.chiaSeeds = chiaSeeds;
}
public void setPumpkinSeeds(String pumpkinSeeds) {
this.pumpkinSeeds = pumpkinSeeds;
}
@Override
public String toString() {
return "Bread with " + spread + ", topped with " + chiaSeeds + " and " + pumpkinSeeds;
}
}
// Builder Interface
interface BreadBuilder {
BreadBuilder addBread();
BreadBuilder addChocolateSpread();
BreadBuilder addChiaSeeds();
BreadBuilder addPumpkinSeeds();
Bread build();
}
// Concrete Builder
class ChocolateBreadBuilder implements BreadBuilder {
private Bread bread = new Bread();
@Override
public BreadBuilder addBread() {
bread.setBread("Whole grain bread");
return this;
}
@Override
public BreadBuilder addChocolateSpread() {
bread.setSpread("Chocolate spread");
return this;
}
@Override
public BreadBuilder addChiaSeeds() {
bread.setChiaSeeds("Chia seeds");
return this;
}
@Override
public BreadBuilder addPumpkinSeeds() {
bread.setPumpkinSeeds("Pumpkin seeds");
return this;
}
@Override
public Bread build() {
return bread;
}
}
// Client Code
public class Main {
public static void main(String[] args) {
// Create a builder and build the chocolate spread bread
BreadBuilder builder = new ChocolateBreadBuilder();
Bread myBread = builder.addBread()
.addChocolateSpread()
.addChiaSeeds()
.addPumpkinSeeds()
.build();
// Output the result
System.out.println(myBread);
}
}
팩토리 패턴의 핵심 요소:
// Product Interface
interface Juice {
void serve();
}
// Concrete Product 1
class OrangeJuice implements Juice {
@Override
public void serve() {
System.out.println("Serving Orange Juice.");
}
}
// Concrete Product 2
class MangoJuice implements Juice {
@Override
public void serve() {
System.out.println("Serving Mango Juice.");
}
}
// Creator Abstract Class
abstract class JuiceFactory {
// Factory method
public abstract Juice createJuice();
}
// Concrete Creator 1
class OrangeJuiceFactory extends JuiceFactory {
@Override
public Juice createJuice() {
return new OrangeJuice();
}
}
// Concrete Creator 2
class MangoJuiceFactory extends JuiceFactory {
@Override
public Juice createJuice() {
return new MangoJuice();
}
}
// Client Code
public class Main {
public static void main(String[] args) {
// Create an Orange Juice using its factory
JuiceFactory orangeJuiceFactory = new OrangeJuiceFactory();
Juice orangeJuice = orangeJuiceFactory.createJuice();
orangeJuice.serve(); // Output: Serving Orange Juice.
// Create a Mango Juice using its factory
JuiceFactory mangoJuiceFactory = new MangoJuiceFactory();
Juice mangoJuice = mangoJuiceFactory.createJuice();
mangoJuice.serve(); // Output: Serving Mango Juice.
}
}
이 디자인 패턴은 주로 클래스와 객체가 더 큰 구조를 형성하도록 구성되는 방식에 중점을 둡니다. 객체와 클래스 간의 구성과 관계에 중점을 두고 구조를 단순화하고 유연성을 강화하며 유지 관리성을 향상시킵니다.
어댑터 패턴의 핵심 요소:
// Target Interface (Menu)
interface Menu {
void orderDish(String dish);
}
// Adaptee (Chef)
class Chef {
public void prepareDish(String dishName) {
System.out.println("Chef is preparing " + dishName + ".");
}
}
// Adapter (Waiter)
class Waiter implements Menu {
private Chef chef;
public Waiter(Chef chef) {
this.chef = chef;
}
@Override
public void orderDish(String dish) {
chef.prepareDish(dish);
}
}
// Client Code
public class Restaurant {
public static void main(String[] args) {
Chef chef = new Chef();
Menu waiter = new Waiter(chef);
// Customer places an order via the waiter
waiter.orderDish("Spaghetti Carbonara"); // Output: Chef is preparing Spaghetti Carbonara.
}
}
Key essentials of the facade design pattern:
An example of facade design pattern:
The example illustrates the Facade Pattern which simplifies the process of washing, drying, and pressing clothes. It hides the complexity of interacting with multiple subsystems behind a single, unified interface.
// Subsystem Classes
class WashingMachine {
public void wash() {
System.out.println("Washing clothes.");
}
}
class Dryer {
public void dry() {
System.out.println("Drying clothes.");
}
}
class Iron {
public void press() {
System.out.println("Pressing clothes.");
}
}
// Facade Class
class LaundryFacade {
private WashingMachine washingMachine;
private Dryer dryer;
private Iron iron;
public LaundryFacade(WashingMachine washingMachine, Dryer dryer, Iron iron) {
this.washingMachine = washingMachine;
this.dryer = dryer;
this.iron = iron;
}
public void doLaundry() {
System.out.println("Starting the laundry process...");
washingMachine.wash();
dryer.dry();
iron.press();
System.out.println("Laundry process complete.");
}
}
// Client Code
public class Main {
public static void main(String[] args) {
WashingMachine washingMachine = new WashingMachine();
Dryer dryer = new Dryer();
Iron iron = new Iron();
LaundryFacade laundryFacade = new LaundryFacade(washingMachine, dryer, iron);
// Use the facade to do the laundry
laundryFacade.doLaundry();
}
}
The patterns that fall under this category mainly deals with communication between objects and how they interact with each other.
Example of iterator pattern:
This example demostrates a simple usecase of iterators a employees object using iterator pattern.
// Iterator Interface
interface Iterator {
boolean hasNext();
Object next();
}
// Aggregate Interface
interface Aggregate {
Iterator createIterator();
}
// Employee Class
class Employee {
public String Name;
public int Age;
public String Department;
public int EmployeeId;
public Employee(String name, int age, String department, int employeeId) {
this.Name = name;
this.Age = age;
this.Department = department;
this.EmployeeId = employeeId;
}
}
// Concrete Aggregate
class EmployeeCollection implements Aggregate {
private Employee[] employees;
public EmployeeCollection(Employee[] employees) {
this.employees = employees;
}
@Override
public Iterator createIterator() {
return new EmployeeIterator(this.employees);
}
}
// Concrete Iterator
class EmployeeIterator implements Iterator {
private Employee[] employees;
private int position = 0;
public EmployeeIterator(Employee[] employees) {
this.employees = employees;
}
@Override
public boolean hasNext() {
return position < employees.length;
}
@Override
public Object next() {
return hasNext() ? employees[position++].Name : null;
}
}
// Client Code
public class Main {
public static void main(String[] args) {
// Creating employee array
Employee[] employees = {
new Employee("John", 28, "Engineering", 101),
new Employee("Jane", 32, "Marketing", 102),
new Employee("Tom", 25, "Sales", 103)
};
// Creating employee collection and iterator
EmployeeCollection employeeCollection = new EmployeeCollection(employees);
Iterator iterator = employeeCollection.createIterator();
// Iterating through employees
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
}
}
1.Strategy Interface: Defines the common interface for all supported algorithms.
2.Concrete Strategies: Implement the Strategy interface with specific algorithms.
3.Context: Uses a Strategy to execute the algorithm.
Example of strategy pattern:
Imagine we are building an encoding system where we may need to use different encoding algorithms depending on the situation. We will demonstrate this system using the Strategy Pattern.
// Strategy Interface
interface EncoderStrategy {
void encode(String string);
}
// Concrete Strategy for Base64 Encoding
class Base64Encoder implements EncoderStrategy {
@Override
public void encode(String string) {
// Implement Base64 encoding logic here
System.out.println("This method uses Base64 encoding algorithm for: " + string);
}
}
// Concrete Strategy for MD5 Encoding
class MD5Encoder implements EncoderStrategy {
@Override
public void encode(String string) {
// Implement MD5 encoding logic here
System.out.println("This method uses MD5 encoding algorithm for: " + string);
}
}
// Context Class
class EncoderContext {
private EncoderStrategy strategy;
public void setEncoderMethod(EncoderStrategy strategy) {
this.strategy = strategy;
}
public void encode(String string) {
strategy.encode(string);
}
}
// Usage
public class Main {
public static void main(String[] args) {
EncoderContext context = new EncoderContext();
// Use Base64 encoding method
context.setEncoderMethod(new Base64Encoder());
context.encode("A34937ifdsuhfweiur");
// Use MD5 encoding method
context.setEncoderMethod(new MD5Encoder());
context.encode("89743297dfhksdhWOJO");
}
}
Explanation:
Example of observer pattern:
In a stock trading application, the stock ticker acts as the subject. Whenever the price of a stock is updated, various observers—such as investors and regulatory bodies—are notified of the change. This allows them to respond to price fluctuations in real-time.
import java.util.ArrayList;
import java.util.List;
// Observer interface
interface Observer {
void update(String stockSymbol, double stockPrice);
}
// Subject interface
interface Subject {
void register(Observer o);
void remove(Observer o);
void notify();
}
// Concrete Subject
class Stock implements Subject {
private List<Observer> observers;
private String stockSymbol;
private double stockPrice;
public Stock() {
observers = new ArrayList<>();
}
public void setStock(String stockSymbol, double stockPrice) {
this.stockSymbol = stockSymbol;
this.stockPrice = stockPrice;
notify();
}
@Override
public void register(Observer o) {
observers.add(o);
}
@Override
public void remove(Observer o) {
observers.remove(o);
}
@Override
public void notify() {
for (Observer observer : observers) {
observer.update(stockSymbol, stockPrice);
}
}
}
// Concrete Observer
class StockTrader implements Observer {
private String traderName;
public StockTrader(String traderName) {
this.traderName = traderName;
}
@Override
public void update(String stockSymbol, double stockPrice) {
System.out.println("Trader " + traderName + " notified. Stock: " + stockSymbol + " is now $" + stockPrice);
}
}
// Usage
public class Main {
public static void main(String[] args) {
Stock stock = new Stock();
StockTrader trader1 = new StockTrader("Niharika");
StockTrader trader2 = new StockTrader("Goulikar");
stock.register(trader1);
stock.register(trader2);
stock.setStock("Niha", 9500.00);
stock.setStock("Rika", 2800.00);
}
}
Explanation:
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