Java Generics and Collections, 2nd Edition

Chapter 9. The Collection Interface

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The interface Collection<E> defines the core functionality that we expect of any collection other than a map. It provides methods in four groups: adding elements, removing them, querying the collection’s contents, and making its elements available for further processing.

Adding Elements

boolean add(E e)                           // adds the element e
boolean addAll(Collection<? extends E> c)  // adds 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. So if a method call fails because, for example, it has attempted to add null to a null-hostile collection, it must throw an exception. But calls can succeed without changing the contents of the collection if, for example, they attempt to add an element to a set that already contains it. In this case, the result returned will be false, indicating that the collection ...