Hibernate Tips - delete existing item from children

Scenario as below:

I am at a screen now from a web application.

There is a swap-select box on the screen. I select 5 items and click Save button.

Next, the system creates 1 parent object and saves 5 items (selected from screen's swap-select box) as children(a Set) into their parent.

I leave the screen.

Upon next visit to the same screen again, i am trying to remove 2 among the 5 selected items. After that i click Save button.

How should i handle this?

What i need to do is:

1) Get the original Set from the parent object. (Let's name it 'children')

2) At the same time, create new Set(let's name it 'removedChildren'), add those objects that are meant to be removed. (In this case this new Set will have 2 objects)

3) Using removeAll method from Set, put the 'removedChildren' Set in it (children.removeAll(removedChildren))

4) Set the 'children' Set back to the parent. (parent.setChildren(children))

5) Save the parent. (saveOrUpdate(parent))

How to get the last 2 decimal digits using JAVA?

Example:

To get 0.99
from
double abcd =123456789012345.99;

Solution:
double a = 12345678901234.99*100;
String f = Long.toString(((long) a)%100);