GWT UI that has logic.

LoginView.java

/**
 * A simple login view.
 */
public class LoginView {

	private TextBox username;
	private TextBox password;

	public LoginView(TextBox username, TextBox password) {
		this.username = username;
		this.password = password;
	}

	public boolean validUsernameAndPassword() {
		String inputUsername = username.getText();
		String inputPassword = password.getText();
		return inputUsername.length() > 3 && inputPassword.length() > 3;
	}
}