Collections of apache commons tool class

Commons-collections is an extension and encapsulation of java.util, but its popularity is not as high as java.util, so you can understand it.
org.apache.commons.collections – a set of common interfaces and tool classes customized by Commons Collections org.apache.commons.collections.collection –

a set of classes that implement the java.util.Collection interface

org.apache.commons.collections. comparators – a set of classes that implement the java.util.Comparator interface

org.apache.commons.collections.functors – a set of custom functional classes for Commons Collections org.apache.commons.collections.iterators – a set of classes that

implement the java.util.Iterator interface A set of classes

org.apache.commons.collections.keyvalue - a set of classes that implement collections and key/value mapping related

org.apache.commons.collections.list - a set of classes that implement the java.util.List interface

org.apache. commons.collections.map - a set of classes that implement the Map series of interfaces

org.apache.commons.collections.set - a set of classes that implement the Set series of interfaces

org.apache.commons.collections.bag - a set of classes that implement the Bag interface

org.apache.commons.collections.bidimap - a set of classes that implement the BidiMap family of interfaces

org.apache.commons.collections.buffer - a set of classes that implement the Buffer interface