HashMap Collection:

• HashMap Collection Tutorials & Examples

LinkedHashMap Collection

• Insertion order in LinkedHashMap using java 
• Access order in LinkedHashMap using java 
• Create least recently used (LRU) cache in java using LinkedHashMap

TreeMap Collection:

• Iterate/ loop TreeMap collection of String Objects before & after java8

EnumMap Collection:

• Iterate or loop EnumMap using entrySet & forEach Java 8