Question

I’m searching for a fast and convenient way to add save() and rollback() to a standard Map. Let’s say i have an object ‘table’ of class Table which in turn has a private Map called ‘rows’. What I’m trying to achieve is a fast and without memory waste method for Row to do something like:

row = new Row();
table.addRow(row).setValue("col1", "foo").setValue("col2", "bar").save();
row.setValue("col2", "beer");
System.out.println(table.getRows()); // 1. col1=foo, col2=bar

row.save();
System.out.println(table.getRows()); // 1. col1=foo, col2=beer

Actually, my design is quite trivial: when addRow() is called, i put() the row inside the map; no buffer, no temp elements; i simply pass the entire Row instance to rows collection. But I need a fast method and (if possible) avoiding the duplication of rows.

any idea?

Answer 1

This sounds too much like “I want to have the new and old values in memory, but I do not want to have the new and old values in memory”.

Options:

a) A map of all the added elements, when save do putAll.

b) Your map, instead of <ClassKey, ClassValue>, holds <ClassKey, ClassValue2>. Value2 holds two items of ClassValue, the new and old instance. At save, you pass the new one (if any) to the old one. It will be useful only if you are changing most of the entries in each “transaction”.

Not mentioned is the issue of deleting elements, which will bring you yet more joy. With option 2 you can set a boolean at Value2, with option a you will need more workarounds.