Download Lecture 25

Lecture 25
May 16, 2000
Agenda
• Using JComboBox
• Class ID3V1_Tag
– Using it.
– Implementation.
• Class MP3_File
– Dummy Version
• Quiz
JComboBox
• Constructors
– No-arg
• void addItem( Object ) or void setItemAt( … )
– Array of Objects
• Objects are usually Strings, but don’t have to be.
– Vector
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Object getSelectedItem()
Object[] getSelectedObjects()
void setEditable( boolean )
void setEnabled( boolean )
ID3V1 Tag Structure
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Starts 128 bytes from end of file.
First three bytes contain ASCII “TAG”
Title starts at offset 3 (30 bytes)
Artist starts at offset 33 (30 bytes)
Album starts at offset 63 (30 bytes)
Year starts at offset 93 (4 bytes)
Comment starts at offset 97 (30 bytes)
– If the 29th comment byte is ASCII nul (000000002), then the track
number is a one-byte integer value in the 30th byte of the comment.
• Genre is encoded as an index into an array of Strings.
– Integer value is one byte at offset 127 into the tag.
Sample Code
• [ TagEditor.java ]
– Provides the user with a JComboBox for setting the
genre in the ID3V1 tag of a file.
– Note: If you use this program on a real MP3 file, you
will lose the ID3V2 tag and the audio data in the file!
• [ MP3_File.java ]
• [ ID3V1_Tag.java ]
• [ ID3V2_Tag.java ]
Quiz
• Write an application that puts up a JFrame
with a File->Exit menu item. When the
user clicks on either File->Exit or the
“close” button in the title bar, the
application exits.
• Solutions
– Using static variables: [ Quiz_3a.java ]
– Using instance variables: [ Quiz_3b.java ]