Advanced JavaSession 3

New York University

School of Continuing and Professional Studies

2

Objectives

• Revisit thread Synchronization issues– Updated versions of SynchBankTest and

UnsynchBankTest

• Collection Interfaces• Concrete Collections• Collection Framework• Algorithms• Legacy Collections

3

Synchronization Issues

• Race condition – producer-consumer– When multiple threads try to manipulate the same object,

they may get wrong results.

• Deadlock – dining philosophers– A thread going after a resource that’s held by another

thread, while the other thread needs the resource held by this thread, hence both wait endlessly.

4

Synchronization Examples

• UnsynchBankTest.java– TransferThread– TestThread

• SynchBankTest.java– TransferThread– TestThread

5

Interfaces

• You cannot instantiate an object of type Interface with new.

• You can declare that an object variable will be of that interface type.

• You can use “instanceof” to check if an object implements an interface.

• You cannot put instance fields, or static methods in interfaces.

• You can put constants in interfaces.

6

Implementations

• A class may implement one or more Interfaces using the keyword “implements”

-----

public interface Comparable

{

public int compareTo(Object b)

}

------

Class Employee extends Person implements Comparable

7

Queue Example

1 2 3 4

head tail

Interface Queue{

void add(Object obj);Object remove();int size();

}

8

Circular Array Implementation

head

tail

910

678

9

Linked List Implementation

head tail

1 2 3 4

10

Sort programimport java.util.*;

public class sort { public static void main(String args[]) { List l = Arrays.asList(args); Collections.sort(l); System.out.println(l); }}

11

Collection Interface

• Has three fundamental methods– boolean add (Object obj)– boolean remove (Object obj)– Iterator iterator()

• Other methods– boolean contains(Object obj)– boolean size()– boolean isEmpty()– boolean retainAll(Collection c)– boolean containsAll(Collection c)

12

Iterator Interface

• Has three fundamental methods– Object next()– boolean hasNext()– void remove()

Element1

Element2

Element3

Element4

Element5

next()

13

Concrete Collections

• Linked Lists

• Array Lists

• Hash Sets

• Tree Sets

• Maps

• Week Hash Maps

10

20

30

40

14 17 19

33

42 45

14

Algorithms/Utility methods inCollections class

• Common set of methods that work on all types of Collections and Lists

• min, max – can work on any Collection

• sort, binarySearch, shuffe, reverse, copy, fill – can work on any List

• unmodifiable and synchronized versions of Collections

15

Legacy Collections

• Hashtable

• Enumeration

• Properties