INHERITANCE AND POLYMORPHISM - Introduction to Java Programming: Comprehensive Version - page 433

class, which can be used to store an unlimited number of objects. Figure 11.3 shows some
methods in ArrayList .

java.util.ArrayList<E>

+ArrayList()
+add(o: E): void
+add(index: int, o: E): void
+clear(): void
+contains(o: Object): boolean
+get(index: int): E
+indexOf(o: Object): int
+isEmpty(): boolean
+lastIndexOf(o: Object): int
+remove(o: Object): boolean

Creates an empty list.

Appends a new element o at the end of this list.
Adds a new element o at the specified index in this list.
Removes all the elements from this list.
Returns true if this list contains the element o .
Returns the element from this list at the specified index.
Returns the index of the first matching element in this list.
Returns true if this list contains no elements.
Returns the index of the last matching element in this list.
Removes the first element o from this list. Returns true
if an element is removed.
Returns the number of elements in this list.
Removes the element at the specified index. Returns true
if an element is removed.
Sets the element at the specified index.

+size(): int
+remove(index: int): boolean

+set(index: int, o: E): E

F IGURE 11.3

An ArrayList stores an unlimited number of objects.

ArrayList is known as a generic class with a generic type E . You can specify a concrete
type to replace E when creating an ArrayList . For example, the following statement creates
an ArrayList and assigns its reference to variable cities . This ArrayList object can be
used to store strings.

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

The following statement creates an ArrayList and assigns its reference to variable
dates . This ArrayList object can be used to store dates.

ArrayList<java.util.Date> dates = new ArrayList<java.util.Date> ();

Note
Since JDK 7, the statement

ArrayList<AConcreteType> list = new ArrayList<AConcreteType>();

can be simplified by

ArrayList<AConcreteType> list = new ArrayList<>();

The concrete type is no longer required in the constructor thanks to a feature called
type inference . The compiler is able to infer the type from the variable declaration. More
discussions on generics including how to define custom generic classes and methods
will be introduced in Chapter 19, Generics.

type inference

Listing 11.8 gives an example of using ArrayList to store objects.

L ISTING 11.8

TestArrayList.java
1 import java.util.ArrayList;
2

import ArrayList