Google Web Toolkit - Monthly Payment Calculator

This example displays a simple Loan Calculator. When the user clicks calculate a ClickListener is fired which calculates the monthly payment and dispays it.

This example illustrates GWT Labels, TextBox, and Button controls.

    /*
 * mcintoshEntryPoint.java
 *
 * Created on June 29, 2008, 1:46 PM
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */
package com.client;

import com.google.gwt.core.client.EntryPoint;
import com.client.time.*;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.ClickListener;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.TextBox;
import com.google.gwt.user.client.ui.Widget;

/**
 *
 * @author avalanche
 */
public class mcintoshEntryPoint implements EntryPoint {

    final Label lblLoanAmount = new Label("Loan Amount:");
    final TextBox txtLoanAmount = new TextBox();
    final Label lblLoanLength = new Label("Loan Length (Month):");
    final TextBox txtLoanLength = new TextBox();
    final Label lblInterestRate = new Label("Interest Rate (Yearly):");
    final TextBox txtInterestRate = new TextBox();
    final Button calculate = new Button("Calculate");
    final Label lblResult = new Label("Payment per month:");

    public mcintoshEntryPoint() {
        calculate.addClickListener(new ClickListener() {

            public void onClick(Widget arg0) {
                
                //P = A (1 + r ) ^ N /( 1 + r ) ^ N -1                                                
                int loanAmount = Integer.parseInt(txtLoanAmount.getText());
                int loanLength = Integer.parseInt(txtLoanLength.getText());
                double interestRate = Double.parseDouble(txtInterestRate.getText())/1200;
                double temp = Math.pow(( 1 + interestRate ) , loanLength);
                Double result = new Double((loanAmount * interestRate * temp)   / (temp -1));                                
                lblResult.setText(result.toString());
            }
        });


    }

    /**
     * The entry point method, called automatically by loading a module
     * that declares an implementing class as an entry-point
     */
    public void onModuleLoad() {
        RootPanel.get().add(lblLoanAmount); 
        RootPanel.get().add(txtLoanAmount);        
        RootPanel.get().add(lblLoanLength);
        RootPanel.get().add(txtLoanLength);
        RootPanel.get().add(lblInterestRate);
        RootPanel.get().add(txtInterestRate);
        RootPanel.get().add(calculate);
        RootPanel.get().add(lblResult);

    }
}