compare_collections

Introduction

Compare the contents of two collections, calculating add, sub and update members from collection 1 to 2.

Installation

// just copy my jar to your project!

Usage

Construction method:

// Approach 1: the the most ordinary way
// PK is used to identify an object, T is the very object  
create(Map<PK, T> before, Map<PK, T> after);
// Approach 2: applying two collections and a method that getting PK from the object
create(before, after, t -> t.getId());
// Approach 3: applying two collections with itself as PK
create(before, after);

Getting results:

CompareCollections<> cc = CompareCollections.create(...);
cc.getAddMap();
cc.getSubMap();
cc.getUpdateMap();

Warning:

Approach 2 and 3 may cause java.lang.IllegalStateException: Duplicate key.
This exception is thrown by Collectors.toMap() method.