1. Collections Chapter 12

2. 12 Java Collection Frameworks The Java collection framework is a set of utility classes and interfaces. Designed for working with collections of objects A collection is a group of objects, each of which is known as an element in the collection.

3. 12 Types of Collections Simple Collections Sets have no duplicate elements. Lists are ordered collections that can have duplicate elements. Maps Map uses key/value pairs to associate an object (the value) with a key. Both sets and maps can be sorted or unsorted.

4. 12 The Collection Interface Root interface of collection classes Common methods defined in Collection: add() contains() isEmpty() iterator() remove() size()

5. 12 The ArrayList ArrayList is a concrete implementation of the List interface. A concrete implementation is a class that can be instantiated.

6. 12 ArrayList vs. an Array An ArrayList has several advantages: Can be resized dynamically as more objects are added Elements can be removed from an ArrayList Simpler to use than an array

7. 12 Controlling ArrayList size Important methods: size() returns the number of elements ensureCapacity() sets the capacity of the ArrayList to a certain number of elements trimToSize() trims an ArrayList to only the number of elements it currently holds to reduce memory requirements

8. 12 Using Collections Although objects in a collection do not have to be of the same type: It is not good practice to mix object types in a collection. You must check object type and cast to appropriate class if heterogeneous collections are used.

9. 12 Adding Elements to a Collection add() method is overloaded myList.add(myObject) adds myObject to end of collection myList.add(3, myObject) inserts myObject at offset 3 in a collection

10. 12 Replacing and Removing Elements To replace and remove elements in an ArrayList: set() method replaces an element at a specified position remove() method removes an element at a specified position