Java Generics and Collections, 2nd Edition

Chapter 13. The Collections Class

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The class java.util.Collections consists entirely of static methods that operate on or return collections. There are three main categories: generic algorithms, methods that return empty or prepopulated collections, and methods that create wrappers. We discuss these three categories in turn, followed by a number of other methods which do not fit into a neat classification.

All the methods of Collections are public and static, so for readability we will omit these modifiers from the individual declarations.

Generic Algorithms

The generic algorithms fall into four major categories: changing element order in a list, changing the contents of a list, finding extreme values in a collection, and finding specific values in a list. They represent reusable functionality, in that they can be applied to Lists (or in some cases to Collections) of any type. Generifying the types of these methods has led to ...