converter.java

Generics and the greatly expanded collection libraries have tremendously increased the power of Ja

package com.converter;

import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;

enum Currency { DOLLAR, EURO, POUND }

interface CView extends Observer<CModel,CView,Currency> {}

class RateView extends JTextField implements CView {
    private final CModel model;
    private final Currency currency;

    public RateView(final CModel model,
		      final Currency currency) {
	this.model = model;
	this.currency = currency;
	addActionListener( new ActionListener(){
		public void actionPerformed(ActionEvent e) {
		    double rate = Double.parseDouble( getText() );
		    model.setRate(currency, rate);
		}
	    });
	model.addObserver( this );
    }

    public void update(CModel model, Currency currency) {
	if (this.currency==currency) {
	    double rate = model.getRate(currency);
	    setText(String.format("%10.6f", rate));
	}
    }
}

class ValueView extends JTextField implements CView {
    private final CModel model;
    private final Currency currency;

    public ValueView(final CModel model,
		     final Currency currency) {
	this.model = model;
	this.currency = currency;
	addActionListener( new ActionListener(){
		public void actionPerformed(ActionEvent e) {
		    double value = Double.parseDouble( getText() );
		    model.setValue(currency, value);
		}
	    });
	model.addObserver( this );
    }

    public void update(CModel model, Currency currency) {
	if (currency==null || currency==this.currency) {
	    double value = model.getValue(this.currency);
	    setText(String.format("%15.2f", value));
	}
    }
}

class CModel extends Observable<CModel,CView,Currency> {
    private final EnumMap<Currency,Double> rates;
    private long value;  // in cents
    public CModel() {
	rates = new EnumMap<Currency,Double>(Currency.class);
    }
    public void initialize(double... initialRates) {
	for (int i=0; i<initialRates.length; i++)
	    setRate(Currency.values()[i], initialRates[i]);
    }
    public void setRate(Currency c, double f) {
	rates.put(c,f);
	setChanged();
	notifyObservers(c);
    }
    public void setValue(Currency c, double v) {
	value = Math.round(v/getRate(c) * 100);
	setChanged();
	notifyObservers(null);
    }
    public double getRate(Currency c) { return rates.get(c); }
    public double getValue(Currency c) { return value*getRate(c)/100; }
}

class Converter extends JFrame {
    public Converter() {
	CModel model = new CModel();
	setTitle( "Currency converter");
	setLayout( new GridLayout( Currency.values().length+1, 3 ) );
	add( new JLabel( "currency" ));
	add( new JLabel( "rate" ));
	add( new JLabel( "value" ));
	for (Currency c : Currency.values()) {
	    add( new JLabel( c.name() ));
	    add( new RateView(model, c) );
	    add( new ValueView(model, c) );
	}
	model.initialize(1.0, 0.83, 0.56);
	setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	pack();
  }
  public static void main(String[] args) {
    new Converter().setVisible( true );
  }
}