Design Patterns Example

WtfWtf.java

import java.util.Date;

import javax.swing.JFrame;
import javax.swing.JTextArea;


public class WtfWtf {

	// concrete logger but uses different interface
	class UiLogger {
		private JTextArea textArea;

		public UiLogger() {
			JFrame frame = new JFrame();
			frame.setSize(400, 500);
			frame.setVisible(true);
			textArea = new JTextArea();
			frame.add(textArea);
		}
		
		public void addMessage(String text) {
			textArea.setText(textArea.getText() + "\n" + text);
		}
	}
	
	// the log interface to unify all the logging things!
	interface Log {
		public void log(String string);
	}
	
	// just an implementation of a log
	class ConsoleLogger implements Log {
		@Override
		public void log(String string) {
			System.out.println(string);
		}
	}
	
	// adapter pattern - we adapt the different interface to log interface
	class UiLogAdapter implements Log {
		private UiLogger logger;
		public UiLogAdapter(UiLogger logger) {
			this.logger = logger;
		}
		@Override
		public void log(String string) {
			logger.addMessage(string);
		}
	}
	
	// composite pattern - log to multiple places
	class CompositeLogger implements Log {
		private Log[] logs;
		public CompositeLogger(Log[] logs) {
			this.logs = logs;
		}
		@Override
		public void log(String string) {
			for (Log log : logs) log.log(string);
		}
	}
	
	// decorator pattern - when logging, log current time too
	class DateLogDecorator implements Log {
		private Log log;
		public DateLogDecorator(Log log) {
			this.log = log;
		}
		@Override
		public void log(String string) {
			log.log(String.format("[%tT] %s", new Date(), string));
		}
	}
	
	// main code
	public void run() {
		Log[] logs = { new UiLogAdapter(new UiLogger()),
					   new ConsoleLogger() };
		Log log = new CompositeLogger(logs);
		log = new DateLogDecorator(log);
		log.log("start program");
		log.log("connect to database");
		try { Thread.sleep(1000); } catch (InterruptedException e) { }
		log.log("connect finished");
		
		// armse pattern - log "armse" for all debugging purposes
		log.log("armse");
		
	}
	
	public static void main(String[] args) {
		new WtfWtf().run();
	}
	
}