ArrayLists and Iterators

Read this chapter about lists and the useful methods that are available for adding and inserting elements into a list.

5. Example Program

Answer:
You can encapsulate your integers in Integer objects and store them in an ArrayList.

Example Program

import java.util.* ;

public class ArrayListEg
{

  public static void main ( String[] args)
  {
    // Create an ArrayList that holds references to String
    ArrayList<String> names = new ArrayList<String>();

    // Add three String references
    names.add("Amy");
    names.add("Bob");
    names.add("Cindy");
       
    // Access and print out the three String Objects
    System.out.println("element 0: " + names.get(0) );
    System.out.println("element 1: " + names.get(1) );
    System.out.println("element 2: " + names.get(2) );
  }
}

The example program creates an ArrayList that holds String references and then adds references to three Strings. The statement

ArrayList<String> names = new ArrayList<String>();

creates an ArrayList of String references. The phrase <String> can be read as "of String references". Note that there are "angle brackets" on each side of <String>.

The phrase ArrayList<String> describes both the type of the object that is constructed (an ArrayList) and the type of data it will hold (references to String).

ArrayList is a generic type, which means that its constructor specifies both the type of object to construct and the type that the new object will hold. The type the object will hold is placed inside angle brackets like this: <DataType>. Now, when the ArrayList object is constructed, it will hold data of type "reference to DataType".

A program must import the java.util package to use ArrayList.

By default, an ArrayList starts out with 10 empty cells.

Question 5:
Examine the following:
    ArrayList<Integer> values = new ArrayList<Integer>();
What type of data will values hold?