private void jCheckBox1ActionPerformed(java.awt.event.ActionEvent evt) {
   if (jCheckBox1.isSelected() == true){
        int value1 = jSlider3.getValue();
    }
    else
    {
        int value1 = 0;
    }
}

private void jCheckBox2ActionPerformed(java.awt.event.ActionEvent evt) {
     if (jCheckBox2.isSelected() == true){
        int value2 = jSlider1.getValue();
    }
    else
    {
        int value2 = 0;
    }
}

public void addvalues() {

jCheckBox1ActionPerformed();
jCheckBox2ActionPerformed();

//code for addition

value = value1 + value2;
}