help me to do below method.

/**

* Populates the vars list with simple variables, and arrays lists with arrays

* in the expression. For every variable (simple or array), a SINGLE instance is created

* and stored, even if it appears more than once in the expression.

* At this time, values for all variables and all array items are set to

* zero - they will be loaded from a file in the loadVariableValues method.

*

* @param expr The expression

* @param vars The variables array list - already created by the caller

* @param arrays The arrays array list - already created by the caller

*/

public static void

makeVariableLists(String expr, ArrayList vars, ArrayList arrays) {

//help me with this method.

vars.add(null);

arrays.add(null);

}