List ADT Generic Array Implementation

1
List ADTGenericArray Implementation

• IC312

2
Array-based Listusing Objects

• class CoinCounter
• private MyList list
• public CoinCounter(MyList l)
• list l
• public int run()
• int total0
• for (int i0 iltlist.size() i)
• if (list.get(i) instanceof Coin)
• Coin coin (Coin)list.get(i)
• totalcoin.getValue()
• return total

3
Generics

• Define classes that work with any type of object
• Eliminate the need to cast Objects to their
  underlying type
• Let Java enforce restrictions on the type of
  objects
• Enforcement occurs at compile time. Avoids
  runtime errors!

4
Coin Holder

• public class Holder1
• private Coin item1, item2
• public Holder1(Coin it1, Coin it2)
• item1 it1
• item2 it2
• public Coin getItem1()
• return item1
• public Coin getItem2()
• return item2
• public class HolderTest
• public static void main(String args)
• Holder1 h1 new Holder1(new Coin(1, 10),
  new Coin(2, 20))
• Coin c1 h1.getItem1()
• Coin c2 h1.getItem2()

5
Object Holder

• public class Holder2
• private Object item1, item2
• public Holder1(Object it1, Object it2)
• item1 it1
• item2 it2
• public Object getItem1()
• return item1
• public Object getItem2()
• return item2
• public class HolderTest
• public static void main(String args)
• Holder2 h2 new Holder2(new Coin(1, 10),
  new Coin(2, 20))
• Coin c1 (Coin)h2.getItem1()
• Coin c2 (Coin)h2.getItem2()

6
Generic Holder

• public class Holder3ltEgt
• private E item1, item2
• public Holder3(E it1, E it2)
• item1 it1
• item2 it2
• public E getItem1()
• return item1
• public E getItem2()
• return item2
• public class HolderTest
• public static void main(String args)
• Holder3ltCoingt h3 new Holder3ltCoingt(new
  Coin(1, 10),
• new
  Coin(2, 20))
• Coin c1 h3.getItem1()

7
Object List Interface

• public interface List
• int size()
• boolean isEmpty()
• Object get(int index)
• Object set(int index, Object entry)
• boolean add(Object entry)
• boolean add(int index, Object entry)
• Object remove(int index)

8
Generic List Interface

• public interface ListltEgt
• int size()
• boolean isEmpty()
• E get(int index)
• E set(int index, E entry)
• boolean add(E entry)
• boolean add(int index, E entry)
• E remove(int index)

9
Generic List Implementation

• public class AListltEgt implements ListltEgt
• private int size
• private final int MAX_SIZE 50
• private E array
• public AListGeneric()
• array (E)(new ObjectMAX_SIZE)
• size 0
• public int size()return size
• public boolean isEmpty() return (size 0)
• public E get(int index) throws
  IndexOutOfBoundsException
• if (index gt 0 index lt size)
• return arrayindex
• else
• throw new IndexOutOfBoundsException("index
  " index)

This syntax is a work around for arrays only.
Arrays are a special case when it comes to
generics.
10
Object Version of Remove

• public Object remove(int index) throws
  IndexOutOfBoundsException
• if (index gt 0 index lt size)
• Object temp arrayindex
• for(int i index i lt size-1 i)
• arrayi arrayi1
• arraysize-1 null
• size--
• return temp
• else
• throw new IndexOutOfBoundsException()

What does the generic version look like?
11
Generic Version of Remove

• public E remove(int index) throws
  IndexOutOfBoundsException
• if (index gt 0 index lt size)
• E temp arrayindex
• for(int i index i lt size-1 i)
• arrayi arrayi1
• arraysize-1 null
• size--
• return temp
• else
• throw new IndexOutOfBoundsException()