Course Introduction

1
Course Introduction

• J2ME Example

2
Introduction

• The MIDP provides a mechanism for MIDlets to
  persistently store data and retrieve it later
• This persistent storage mechanism, called the
  Record Management System (RMS), is modeled after
  a simple record-oriented database

3
Introduction

• Only allow the manipulation of the MIDlet suites
  own record stores
• Do not provide any mechanism for record sharing
  between MIDlets in different MIDlet suites
• Record store names are case sensitive
• up to 32 Unicode characters

4
Records

• Records are arrays of bytes
• Developers can use
• DataInputStream
• DataOutputStream
• ByteArrayInputStream
• ByteArrayOutputStream

5
Records

• Records are uniquely identified within their
  record_Id (integer) as the primary key for the
  records
• The first record created in a record store will
  have record_Id equal to 1, and each subsequent
  record_Id will monotonically increase by one

6
Records
7
Classes for Record Store

• Package
• javax.microedition.rms
• Classes
• RecordStore, RecordEnumeration
• Interfaces
• RecordComparator, RecordFilter, RecordListener

8
Management of Record Store

• openRecordStore()
• closeRecordStore()
• listRecordStore()
• deleteRecordStore()
• getVersion(), getLastModified()

9
Record Manipulation

• Basic manipulation
• addRecord(), deleteRecord(), and getRecord(),
  setRecord()
• Information retrieval
• getNumRecords() , getRecordSize()
• Information about a record
• getSize(), getSizeAvailable()
• Enumeration
• getNextRecordID()

10
Basic Record Manipulation

• addRecord
• int addRecord(byte data, int offset, int
  numBytes)
• Adds a new record to the record store
• The recordId for this new record is returned

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Basic Record Manipulation

• deleteRecord
• void deleteRecord(int recordId)
• The record is deleted from the record store
• getRecord
• int getRecord(int recordId, byte buffer, int
  offset)
• Returns the data stored in the given record

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Basic Record Manipulation

• setRecord
• void setRecord(int recordId, byte newData, int
  offset, int nBytes)
• Sets the data in the given record

13
ByteArrayOutputStream
14
ByteArrayInputStream
15
Monitoring Record Changing

• RecordListener
• recordAdded(recordStore, recordID)
• recordChanged(recordStore, recordID)
• recordDeleted(recordStore, recordID)
• RecordStore
• addRecordListener(listener)
• removeRecordListener(listener)

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Information retrieval

• getNumRecords
• Returns the number of records currently in the
  record store
• getRecordSize
• Returns the size (in bytes) of the MIDlet data
  available in the given record

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Information about a record

• getSize
• Returns the amount of space, in bytes, that the
  record store occupies
• getSizeAvailable
• Returns the amount of additional room (in bytes)
  available for this record store to grow

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Enumeration

• getNextRecordID
• Returns the record_Id of the next record to be
  added to the record store

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Record Enumeration

• An interface logically maintains a sequence of
  the record_Id's of the records in a record store
• Methods
• hasNextElement(), hasPreviousElement()
• nextRecord(), nextRecordId()
• previousRecord(), previousRecordId()

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Record Enumeration
21
Record Comparator

• An interface defining a comparator which compares
  two records to see if they match or what their
  relative sort order is
• int compare(byte rec1, byte rec2)
• Returns
• PROCEEDS, FOLLOWS, EQUIVALENT

22
Example