Comparing maps

Using a combination of cloning constructors and removeAll() for subsetting…

Map<String, String> beforeMap = new HashMap<String, String>();
beforeMap.put("a", "1");
beforeMap.put("b", "2");
beforeMap.put("c", "3");
Map<String, String> afterMap = new HashMap<String, String>();
afterMap.put("a", "1");
afterMap.put("c", "333");

Code

Set<String> removedKeys = new HashSet<String>(beforeMap.keySet());
removedKeys.removeAll(afterMap.keySet());

Set<String> addedKeys = new HashSet<String>(afterMap.keySet());
addedKeys.removeAll(beforeMap.keySet());

Set<Entry<String, String>> changedEntries = new HashSet<Entry<String, String>>(afterMap.entrySet());
changedEntries.removeAll(beforeMap.entrySet());

System.out.println("added " + addedKeys);
System.out.println("removed " + removedKeys);
System.out.println("changed " + changedEntries);

Output

added []
removed [b]
changed [c=333]