Evento asociado al cambiar el contenido de un textbox

[Slackin]

Gracias. he logrado resolverlo como uds indicaban. Ahora el programa está terminado y se ve así:

Código Java:

import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;
import javax.swing.JTextField;
 
public class Cap12_Acumular extends Applet implements ActionListener {
 
    private Button year, ingresar;
    private TextField interestField, amountField, outcome;
    private Investment myMoney;
 
    public void init() {
        Label amountLabel = new Label("Enter amount:");
        add(amountLabel);
 
        amountField = new TextField(10);
        add(amountField);
        amountField.addActionListener(this);
 
        Label rateLabel = new Label("Enter interest rate");
        add(rateLabel);
        
        interestField = new TextField(4);
        add(interestField);
        interestField.addActionListener(this);
 
        year = new Button ("Calcular");
        add(year);
        year.addActionListener(this);
 
        Label outcomeLabel = new Label("Your money at the end of the year is");
        add(outcomeLabel);
 
        outcome = new TextField(20);
        add(outcome);
 
        myMoney = new Investment();
    }
 
    public void actionPerformed(ActionEvent event) {
        
        if(event.getSource() instanceof TextField)
            if(event.getSource().equals(amountField)){
                float amount = Integer.parseInt(amountField.getText());
                myMoney.setInitialAmount(amount);
            }
            else{
                float rate = Float.parseFloat(interestField.getText());
                myMoney.setRate(rate);
            }
                 
         if (event.getSource() == year) {
            myMoney.anotherYear();
            float newAmount = myMoney.getNewAmount();
            int dollars = (int) newAmount;
            int cents = Math.round(100.0f * (newAmount - dollars));
            outcome.setText(dollars + " dollars " + cents + " cents");
        }
    }
}
 
class Investment {
 
    private float interestRate;
    private float oldAmount, newAmount;
 
    public void setInitialAmount(float amount) {
        oldAmount = amount;
    }
 
    public void setRate(float rate) {
        interestRate = rate;
    }
 
    public void anotherYear() {
        newAmount = oldAmount + (oldAmount * interestRate / 100.0f);
        oldAmount = newAmount;
    }
 
    public float getNewAmount() {
        return newAmount;
    }
}