String / DecimalFormat __java.lang.NumberFormatException：对于输入字符串：“”

Question

我正在尝试将String从一个类带到另一个类，但是出现以下错误：

java.lang.NumberFormatException：对于输入字符串：“”

“主班”是这样的：

import java.text.DecimalFormat;

public class calculadora_de_cuotas extends javax.swing.JFrame {
    String divimmtt="";

    public String getDivimmtt() {
        return divimmtt;
    }

    public void setDivimmtt(String divimmtt) {
        this.divimmtt = divimmtt;
    }

    public void calculoINTYK() {

       int monto = Integer.parseInt(txtmonto.getText());
       int tiempo = Integer.parseInt(txttiempo.getText());
       int interes = Integer.parseInt(txtporciento.getText());

       double interescalcu = 0.01 * interes;

       montint = monto * interescalcu; 
       mitiem = montint * tiempo; 
       double monmitiem = monto + mitiem;
       double divimmt = monmitiem / tiempo;

       DecimalFormat formato2 = new DecimalFormat("#.##");
       this.divimmtt = (formato2.format(divimmt));            
       calculado.setText(divimmtt);
    }
}

这是另一堂课*

import javax.swing.JOptionPane;
public class AsignarPrestamo extends javax.swing.JFrame {

    private void asd(){
        try{
            calculadora_de_cuotas cdc = new calculadora_de_cuotas();
            cdc.calculoINTYK();
            String xx = cdc.getDivimmtt();

            JOptionPane.showMessageDialog(null, xx);
            System.out.println(xx);
        } catch(NumberFormatException mmk){
            System.out.println(mmk);
        }
    }
}