import javax.swing.JOptionPane;public class InputDemo4{  String str = "两数之和是：";  float number1,number2;  public InputDemo4(){    number1 = Float.parseFloat(JOptionPane.showInputDialog("请输入一个实数："));        number2 = Float.parseFloat(JOptionPane.showInputDialog("请输入一个实数："));    str = str + (number1+number2);    JOptionPane.showMessageDialog(null,str);  }  public static void main(String[] args){    InputDemo4 ct = new InputDemo4();    System.exit(0);  }}