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JAXX Demo
There is a newer version: 3.0-alpha-6
/*
 * #%L
 * JAXX :: Demo
 * %%
 * Copyright (C) 2008 - 2014 Code Lutin, Tony Chemit
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as 
 * published by the Free Software Foundation, either version 3 of the 
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public 
 * License along with this program.  If not, see
 * .
 * #L%
 */

package jaxx.demo.fun;

import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.math.BigDecimal;

public class CalculatorEngine {
    public static final String DISPLAY_TEXT_PROPERTY = "displayText";

    public static final int ADD = 0;

    public static final int SUBTRACT = 1;

    public static final int MULTIPLY = 2;

    public static final int DIVIDE = 3;

    public static final int RESULT = 4;

    private int operation = -1;

    private boolean clear = true; // true to clear on next key

    private String displayText = "0";

    private BigDecimal value;

    private PropertyChangeSupport propertyChangeSupport = new PropertyChangeSupport(this);


    public String getDisplayText() {
        return displayText;
    }


    public void setDisplayText(String displayText) {
        String oldDisplayText = this.displayText;
        this.displayText = displayText;
        firePropertyChange(DISPLAY_TEXT_PROPERTY, oldDisplayText, displayText);
    }


    public void clear() {
        clearEntry();
        value = new BigDecimal(0);
        operation = -1;
    }


    public void clearEntry() {
        setDisplayText("0");
        clear = true;
    }


    private void checkClear() {
        if (clear) {
            setDisplayText("");
            clear = false;
        }
    }


    public void digit(int digit) {
        checkClear();
        setDisplayText(getDisplayText() + String.valueOf(digit));
    }


    public void dot() {
        checkClear();
        if (getDisplayText().indexOf('.') == -1) {
            if (getDisplayText().length() == 0) {
                setDisplayText("0.");
            } else {
                setDisplayText(getDisplayText() + '.');
            }
        }
    }


    public void toggleSign() {
        String text = getDisplayText();
        if (text.startsWith("-")) {
            text = text.substring(1);
        } else if (!text.equals("0")) {
            text = '-' + text;
        }
        setDisplayText(text);
    }


    public void equal() {
        BigDecimal displayValue = new BigDecimal(getDisplayText());
        BigDecimal newValue = displayValue;
        switch (operation) {
            case ADD:
                newValue = value.add(displayValue);
                break;
            case SUBTRACT:
                newValue = value.subtract(displayValue);
                break;
            case MULTIPLY:
                newValue = value.multiply(displayValue);
                break;
            case DIVIDE:
                newValue = value.divide(displayValue, 8, BigDecimal.ROUND_HALF_UP);
                break;
        }
        value = newValue;
        setDisplayText(toString(newValue));
        clear = true;
        operation = -1;
    }


    public static String toString(BigDecimal decimal) {
        // can't use stripTrailingZeros, as it wasn't introduced until 1.5
        String result = decimal.toString();
        if (result.indexOf(".") != -1) {
            while (result.endsWith("0")) {
                result = result.substring(0, result.length() - 1);
            }
            if (result.endsWith(".")) {
                result = result.substring(0, result.length() - 1);
            }
        }
        return result;
    }


    public void operation(int operation) {
        if (this.operation != -1) {
            equal();
        } else {
            value = new BigDecimal(getDisplayText());
            clear = true;
        }
        this.operation = operation;
    }


    public void add() {
        operation(ADD);
    }


    public void subtract() {
        operation(SUBTRACT);
    }


    public void multiply() {
        operation(MULTIPLY);
    }


    public void divide() {
        operation(DIVIDE);
    }


    public void addPropertyChangeListener(PropertyChangeListener listener) {
        propertyChangeSupport.addPropertyChangeListener(listener);
    }


    public void addPropertyChangeListener(String property, PropertyChangeListener listener) {
        propertyChangeSupport.addPropertyChangeListener(property, listener);
    }


    public void removePropertyChangeListener(PropertyChangeListener listener) {
        propertyChangeSupport.removePropertyChangeListener(listener);
    }


    public void removePropertyChangeListener(String property, PropertyChangeListener listener) {
        propertyChangeSupport.removePropertyChangeListener(property, listener);
    }


    protected void firePropertyChange(String property, Object oldValue, Object newValue) {
        propertyChangeSupport.firePropertyChange(property, oldValue, newValue);
    }
}