jaxx.demo.CalculatorEngine Maven / Gradle / Ivy

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package jaxx.demo;

import java.beans.*;
import java.math.*;

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);
    }
}