Java Generics and Collections, 2nd Edition

Chapter 10. The Collection Interface

The interface Collection<E> is at the root of the type hierarchy of the Collections Framework. It exposes the core functionality that we expect of any collection other than a map.

The Methods of Collection

The methods defined by Collection can be divided into four groups, for adding elements, removing them, querying them, and making them available for further processing.

Note

The code examples for this chapter can be found at:

https://github.com/MauriceNaftalin/JGC_2e_Book_Code/blob/main/src/main/java/org/jgcbook/chapter10

Adding Elements

boolean add(E e)	add the element e
boolean addAll(Collection<? extends E> c)	add the contents of c

The contracts for these methods specify that after their execution, the collection must contain the element or elements supplied in the argument. The return value indicates whether the method call has changed the contents of the collection. So for example, a call attempting to add an element to a set that already contains it will return normally, with the value false. If the collection did not contain the element or elements, and the method was unable to add them, it must throw an exception. This can happen because the collection may not support these operations, or because the method is attempting to add an element that is unacceptable to the collection—​for example, it may be attempting to add null to a null-hostile collection.

To maintain the type uniformity of the collection, these methods only allow ...