Main differences between a Set and a Map in Java are:

1. Duplicate Elements: A Set does not allow inserting

duplicate elements. A Map does not allow using duplicate

keys, but it allows inserting duplicate values for unique

keys.

2. Null values: A Set allows inserting maximum one null

value. In a Map we can have single null key at most and

any number of null values.

3. Ordering: A Set does not maintain any order of elements.

Some of sub-classes of a Set can sort the elements in an

order like LinkedHashSet. A Map does not maintain any

order of its elements. Some of its sub-classes like

TreeMap store elements of the map in ascending order of

keys.

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