Introduction to Programming

Collections vs arrays

All collections are data structures similar to arrays in the sense that they also contain elements, and each is represented by an object of a class. There are two significant differences between arrays and collections, though:

• An array requires assigning a size when instantiated, while a collection increases and decreases in size automatically when elements are added or removed.
• An element of a collection cannot be a value of a primitive type, but only a reference type, including wrapper classes such as Integer or Double. The good news is that you can add a primitive value:

       List list = new ArrayList();       list.add(42);

The boxing conversion (see Chapter 9, Operators, Expressions, and Statements) in the preceding statement ...