Here are some common objects in Java that are used. It is better to know the difference of some very similar objects with almost the same functionality.
1.) StringBuilder and StringBuffer
StringBuilder is faster than StringBuffer, becasue StringBuilder is not synchronized, but be careful it is not thread safe. Then everything else is the similarly the same in terms of functionality. It can append, delete, and concatenate Strings. Therefore you may decide which is suited for your usage.
2.) HashTable and HashMap
This one is also has the difference of not synchronized and thread safe. HashMap performs faster… but then its non synchronized. HashTable would be the opposite then. There is also the ConcurrentHashMap which an new version of HashTable. Other difference is that HashTable does not allow null.
3.) List and Collections
Basically List just inherits the Collection class. List and Collection can do these:
a. ) add and remove items ( in First-in-First-out basis )
b. ) iterate and query its size
But here ‘s what add on to the List ( Only List can do )
a. ) get element in a specified position
b. ) add / delete an element in a specified postion