numericfield.java

learning java的源代码。书中每个实例都有相关的代码example。

//file: NumericField.java
package magicbeans;
import javax.swing.JTextField;
import java.awt.event.*;
import java.beans.*;

public class NumericField extends JTextField
                          implements ActionListener {
    private double value;

    public NumericField(  ) {
        super(6);
        addActionListener( this );
    }

    public void actionPerformed( ActionEvent e ) {
        try {
            setValue( Double.parseDouble( getText(  ) ) );
        } catch ( NumberFormatException ex ) {
            select(0, getText().length(  ));
        }
    }

    public double getValue(  ) {
        return value;
    }

    public void setValue( double newValue ) {
        double oldValue = value;
        value = newValue;
        setText( "" + newValue );
        firePropertyChange( "value", oldValue, newValue );
    }
}