checkboxes in the output

Hi,

In the o/p screen i have 4 push buttons checkall,uncheckall,change,export.There were few records present in the o/p screen and beside each record there is a checkbox.Now if the checkall pushbutton is clicked,then all the checkboxes have to be selected.If the uncheckall pushbutton is clicked,the all the checkboxes have to be unchecked.If the change pushbutton is clicked,then the control should go to next screen.How can I write the code for all the checkboxes to be selected or unselected?

Regards,

Hema