List

1
List
 

• Chapter 5.3- The List Interface
• The List interface is implemented by classes that
  represent an ordered collection of elements.
• The List interface contains four methods
• ListIterator listIterator() returns a list
  iterator of the elements in the list
• Iterator iterator()- returns an iterator of the
  elements in the list
• int size()- returns the number of elements in the
  list
• void add(Object)- adds the specified element to
  the end of the list.

2
Iterator ListIterator
 

• Chapter 5.3- The Iterator and ListIterator
  interfaces
• The Iterator and ListIterator interfaces are used
  by classes that represent a collection of
  objects, and gives us a way to step through the
  objects one at a time.
• The Iterator Interface contains three methods
• boolean hasNext()- returns true if there exists
  another object in the list
• Object next()- returns a reference to the next
  object in the list
• void remove()- removes the object (most recently
  returned by the next method) from the list
• ListIterator contains the above three methods, as
  well as two others
• void add(Object obj)- inserts the object into
  the list immediately after the last element was
  returned by the next method
• void set(Object obj)- replaces the last
  element returned by the next method

3
ArrayList
 

• Chapter 6.7- ArrayList
• ArrayList implements List and is the most basic
  Data Structure in Java
• ArrayList is part of java.util and provides us
  with the same functionality as an array.
• ArrayList stores 1-Dimentional Arrays
• ArrayList stores a list of Objects and references
  them by index.
• An array remains fixed throughout its existance,
  whereas an ArrayList grows and shrinks when
  needed.
• (The Array List class would have been nice to
  use for the PascalsTriangle program.)
• When you change an object that is within an
  ArrayList, you must replace it in the ArrayList.
  The object does not automatically change
  otherwise.
• ArrayList indexes begin at 0 also.

4
ArrayList
 

• Declaring an ArrayList
• Constructor ArrayList()
• Treat an ArrayList like an object.
• ArrayList students new ArrayList()
• Initializing Elements in an ArrayList
• Methods void add(int index, Object obj)
  -inserts object
• void add(Object obj) -adds object to end of
  list
• Person p1 new Person(Mike, Pioro,
  445-43-4456)
• Person p2 new Person(Rich, Johnson,
  421-54-0987)
• Person p3 new Person(Sara, Claxton,
  455-22-1335)
• students.add(1, p1)
• students.add(0, p2)
• students.add(p3)

5
ArrayList
 

• Assigning Elements after initialized
• Methods Object set(int index, Object obj)
  -returns the previous obj
• Student s4 new Student(Colin, Zieroth,
  435-54-8765)
• Student sOld students.set(0, s4)
• Referencing Elements in an ArrayList
• Methods Object get(int index) -returns
  object
• Student sHere students.get(2)
• Removing Elements from an ArrayList
• Methods Object remove(int index) -removes
  object at index Student sRemoved
  students.remove(1)
• Getting the length of the ArrayList
• Methods int size() -returns the number of
  elements
• int length students.size()

6
ArrayList Implementing Iterator
 

• Creating an Iterator to step through the
  ArrayList
• Methods Iterator iterator() returns an
  Iterator of the elements in list
• ListIterator listIterator() returns a
  different type of iterator
• ListIterator listIter students.listIterator()
  
• Implementing an Iterator
• ListIterator listIter students.listIterator()
  
• while (listIter.hasNext())
• System.out.println(((Person)
  iter.next()).getLastName())