This is for an android game. Suppose I have a function that is called several times for second and do some calculations involving an arraylist (or any other complex objects for what matter). Which approach would be preffered?

local:

private void doStuff(){
    ArrayList<Type> XList = new ArrayList<Type>();
    // do stuff with list
}

global:

private ArrayList<Type> XList = new ArrayList<Type>();
private void doStuff(){
    XList.clear();   
    // do stuff with list
}