Java Development Tools

I have a snippnet code jspx

<af:selectBooleanCheckbox text="selectBooleanCheckbox 1" label="Label 1" id="sbc1"

                                              binding="#{bean3.checkbox}" autoSubmit="true"

                                              valueChangeListener="#{bean3.changeValue}"/>

<f:facet name="footer"/>

And code in bean view Scope.

        public void changeValue(ValueChangeEvent valueChangeEvent) {

            // Add event code here...

            System.out.println(checkbox.getValue());

            System.out.println(valueChangeEvent.getOldValue());

            System.out.println(valueChangeEvent.getNewValue());

        }

Result is  false  true false or  true false true.

But I thought that checkbox.getValue() is same value with valueChangeEvent.getOldValue() because ValueChangeListener was called before value of checkbox was updated. Why is that?