CS 596 Client-Server Programming
Assignment 1 Solutions
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San Diego State University -- This page last updated February 29, 1996
Contents of Assignment 1 Solutions Lecture
- Matrix
- Complete Listing
import java.util.*;
class Matrix
{
protected Object[][] matrixElements;
protected static String rowSeperator = "\n";
protected static String columnSeperator = "\t";
protected static String matrixStringHeader = "Matrix(";
protected static String matrixStringTrailer = ")";
public Matrix( int numberOfRows, int numberOfColumns )
{
matrixElements = new Object[numberOfRows][numberOfColumns];
}
public Object elementAt( int row, int column )
{
return matrixElements[ row ][ column ];
}
public void setElementAt( Object data, int row, int column )
{
matrixElements[ row ][ column ] = data;
}
// rowSize = number of columns
public int rowSize()
{
return matrixElements[ 0 ].length;
}
// columnSize = number of rows
public int columnSize()
{
return matrixElements.length;
}
Issues
Array verses Vector
What difference does it make?
Protection level
class Matrix
{
protected Object[][] matrixElements;
verses
class Matrix
{
Object[][] matrixElements;
Storing or computing row and column length
protected int rowSize;
protected int columnSize;
public Matrix( int numberOfRows, int numberOfColumns )
{
rowSize = numberOfColumns;
columnSize = numberOfRows;
matrixElements = new Object[numberOfRows][numberOfColumns];
}
verses code on previous page
Issues
Names
elementAt is Java standard
Names
rowSize verses numberOfColumns verses rowLength
Exceptions - Double check
public Object elementAt( int row, int column )
{
if ( ( row >= 0 ) && ( row < columnSize() ) &&
( column >= 0 ) && ( column < rowSize() ) )
return matrixElements[ row ][ column ];
else
throw new ArrayIndexOutOfBoundsException();
}
verses
public Object elementAt( int row, int column )
{
return matrixElements[ row ][ column ];
}
Exceptions - Who catches?
public Object elementAt( int row, int column )
{
try
{
return matrixElements[ row ][ column ];
}
catch (ArrayIndexOutOfBoundsException e)
{
System.err.println( "Now what do I do? " );
}
}
verses
public Object elementAt( int row, int column )
{
return matrixElements[ row ][ column ];
}
public static void main( String[] args )
{
try
{
Matrix test = new Matrix( 3, 5 );
// code missing
test.elementAt( 10, 20 );
// more stuff
}
catch (ArrayIndexOutOfBoundsException e)
{
//Now handle;
}
More Matrix
public Vector rowAt( int row )
{
Vector rowCopy = new Vector();
for ( int column = 0; column < rowSize(); column++ )
rowCopy.addElement( elementAt( row, column) );
return rowCopy;
}
public Vector columnAt( int column )
{
Vector columnCopy = new Vector();
for ( int row = 0; row < columnSize(); row++ )
columnCopy.addElement( elementAt( row, column ) );
return columnCopy;
}
Issues
Names - Role or What
Vector rowCopy = new Vector();
verses
Vector vector = new Vector();
verses
Vector tempVector = new Vector();
Information Hiding
Vector or Array
rowCopy.addElement( elementAt( row, column) );
verses
rowCopy.addElement( matrixElements[ row ][ column] );
More Matrix
protected static String rowSeperator = "\n";
protected static String columnSeperator = "\t";
protected static String matrixStringHeader = "Matrix(";
protected static String matrixStringTrailer = ")";
public String toString()
{
String matrixAsString = matrixStringHeader + rowSeperator;
for ( int row = 0; row < columnSize(); row++ )
{
matrixAsString += rowToString( row ) + rowSeperator ;
}
return matrixAsString.trim() + matrixStringTrailer;
}
protected String rowToString( int row )
{
String rowAsString = new String();
for ( int column = 0; column < rowSize(); column++ )
{
rowAsString += elementAt( row, column ) + columnSeperator;
}
return rowAsString.trim();
}
Issues
Constants
protected static String rowSeperator = "\n";
Why rowToString?
So can be used by LabeledMatrix toString()
More Matrix
public static Matrix fromString( String matrixString )
throws Exception
{
// stuff removed to save space
}
Issues
Why part of Matrix class
Why static
What happens if string is not a mattrixString?
Labeled Matrix
class LabeledMatrix extends Matrix
{
Hashtable rowLabelToIndex = new Hashtable();
Hashtable columnLabelToIndex = new Hashtable();
public LabeledMatrix( String[] rowLabels, String[] columnLabels)
{
super( rowLabels.length, columnLabels.length );
for ( int row = 0; row < rowLabels.length; row++ )
{
rowLabelToIndex.put( rowLabels[ row ], new Integer( row ) );
}
for ( int column = 0; column < columnLabels.length; column++ )
{
columnLabelToIndex.put( columnLabels[ column ],
new Integer( column ) );
}
}
Issues
Label independence
Use two hashtables not one
Information hiding
Use parent's constructor
Object Safety/Consistancy
Constructor gets labels
Labels not added later
More LabeledMatrix
public Object elementAt( String rowLabel, String columnLabel )
throws NoSuchLabelException
{
int row = labelToIndex( rowLabel, rowLabelToIndex );
int column = labelToIndex( columnLabel , columnLabelToIndex );
return elementAt( row, column );
}
public setElementAt( Object data, String rowLabel,
String columnLabel)
throws NoSuchLabelException
{
int row = labelToIndex( rowLabel, rowLabelToIndex );
int column = labelToIndex( columnLabel , columnLabelToIndex );
super.setElementAt( data, row, column );
}
private int labelToIndex( String label,
Hashtable labelToIndexTable )
throws NoSuchLabelException
{
if ( labelToIndexTable.containsKey( label ) )
{
Integer index = (Integer) labelToIndexTable.get( label );
return index.intValue();
}
else
{
throw new NoSuchLabelException( "No label " + label);
}
}
Issues
Information Hiding
use parent's setElementAt(), elementAt() to access data in matrix
Reduce name space clutterConsistancy
Overload setElementAt(), elementAt()
Abstraction/Information Hiding/Code Reuse
Isolate hashtable access in labelToIndex
Information Hiding
Should user of LabeledMatrix be able to access Matrix's setElementAt(),
elementAt() operations?
Even more HidingOr how paranoid does one get?
public Object elementAt( int row, int column )
throws NoSuchMethodException
{
throw new NoSuchMethodException();
}
public Object elementAt( String rowLabel, String columnLabel )
throws NoSuchLabelException
{
int row = rowIndex( rowLabel );
int column = columnIndex( columnLabel );
return elementAt( row, column );
}
private int rowIndex( String rowLabel )
throws NoSuchLabelException
{
return labelToIndex( rowLabel, rowLabelToIndex );
}
private int columnIndex( String columnLabel )
throws NoSuchLabelException
{
return labelToIndex( columnLabel, columnLabelToIndex );
}
private int labelToIndex( String label,
Hashtable labelToIndexTable )
throws NoSuchLabelException
{
// As before
}
import java.util.*;
class Matrix
{
protected Object[][] matrixElements;
protected static String rowSeperator = "\n";
protected static String columnSeperator = "\t";
protected static String matrixStringHeader = "Matrix(";
protected static String matrixStringTrailer = ")";
public Matrix( int numberOfRows, int numberOfColumns )
{
matrixElements = new Object[numberOfRows][numberOfColumns];
}
public Object elementAt( int row, int column )
{
return matrixElements[ row ][ column ];
}
public void setElementAt( Object data, int row, int column )
{
matrixElements[ row ][ column ] = data;
}
// rowSize = number of columns
public int rowSize()
{
return matrixElements[ 0 ].length;
}
// columnSize = number of rows
public int columnSize()
{
return matrixElements.length;
}
public Vector rowAt( int row )
{
Vector rowCopy = new Vector();
for ( int column = 0; column < rowSize(); column++ )
rowCopy.addElement( elementAt( row, column) );
return rowCopy;
}
public Vector columnAt( int column )
{
Vector columnCopy = new Vector();
for ( int row = 0; row < columnSize(); row++ )
columnCopy.addElement( elementAt( row, column ) );
return columnCopy;
}
public String toString()
{
String matrixAsString = matrixStringHeader + rowSeperator;
for ( int row = 0; row < columnSize(); row++ )
{
matrixAsString += rowToString( row ) + rowSeperator;
}
return matrixAsString.trim() + matrixStringTrailer;
}
protected String rowToString( int row )
{
String rowAsString = new String();
for ( int column = 0; column < rowSize(); column++ )
{
rowAsString += elementAt( row, column ) + columnSeperator;
}
return rowAsString.trim();
}
public static Matrix fromString( String matrixString )
throws Exception
{
Vector rowsString = extractRowsAsStrings( matrixString );
StringTokenizer rowParser;
rowParser = new StringTokenizer( (String) rowsString.elementAt(1),
columnSeperator );
int numberOfRows = rowsString.size();
int numberOfColumns = rowParser.countTokens();
Matrix matrixFromString = new Matrix( numberOfRows ,
numberOfColumns );
for ( int row = 0; row < numberOfRows; row++ )
{
String rowAsString = (String) rowsString.elementAt( row );
rowParser = new StringTokenizer( rowAsString , columnSeperator);
for ( int column = 0; column < numberOfColumns ; column++ )
{
String dataAsString = rowParser.nextToken();
Integer data = new Integer( dataAsString.trim() );
matrixFromString.setElementAt( data, row, column );
}
if ( rowParser.hasMoreTokens() )
throw new Exception( "Bad String as Matrix");
}
return matrixFromString;
}
private static Vector extractRowsAsStrings( String matrixAsString )
{
StringTokenizer matrixParser = new StringTokenizer
( matrixAsString, rowSeperator +
matrixStringTrailer );
// remove header "Matrix(\n"
matrixParser.nextToken();
Vector rowsAsStrings = new Vector();
while ( matrixParser.hasMoreTokens() )
{
rowsAsStrings.addElement( matrixParser.nextToken() );
}
return rowsAsStrings;
}
public static void main( String args[] ) throws Exception
{
Matrix test = new Matrix(3, 5);
for (int row = 0; row < 3; row++)
for (int col = 0; col < 5; col++ )
test.setElementAt( new Integer( row + col), row , col);
System.out.println( test );
System.out.println( test.rowAt( 1) );
System.out.println( test.columnAt( 1) );
System.out.println( Matrix.fromString( test.toString() ));
}
}
class LabeledMatrix extends Matrix
{
Hashtable rowLabelToIndex = new Hashtable();
Hashtable columnLabelToIndex = new Hashtable();
public LabeledMatrix( String[] rowLabels, String[] columnLabels)
{
super( rowLabels.length, columnLabels.length );
for ( int row = 0; row < rowLabels.length; row++ )
{
rowLabelToIndex.put( rowLabels[ row ], new Integer( row ) );
}
for ( int column = 0; column < columnLabels.length; column++ )
{
columnLabelToIndex.put( columnLabels[ column ], new Integer( column ) );
}
}
public Object elementAt( String rowLabel, String columnLabel )
throws NoSuchLabelException
{
int row = labelToIndex( rowLabel, rowLabelToIndex );
int column = labelToIndex( columnLabel ,
columnLabelToIndex );
return elementAt( row, column );
}
public setElementAt( Object data, String rowLabel, String columnLabel)
throws NoSuchLabelException
{
int row = labelToIndex( rowLabel, rowLabelToIndex );
int column = labelToIndex( columnLabel ,
columnLabelToIndex );
super.setElementAt( data, row, column );
}
private int labelToIndex( String label,
Hashtable labelToIndexTable ) throws NoSuchLabelException
{
if ( labelToIndexTable.containsKey( label ) )
{
Integer index = (Integer) labelToIndexTable.get( label );
return index.intValue();
}
else
{
throw new NoSuchLabelException( "No label " + label);
}
}
public static void main( String args[] )
{
String[] rowLabels = { "sam", "pete", "roger" };
String[] columnLabels = { "exam", "final", "roger" };
LabeledMatrix test = new LabeledMatrix( rowLabels, columnLabels);
test.setElementAt( new Integer(5), "sam" , "final");
System.out.println( test );
System.out.println( test.rowAt( 1) );
System.out.println( test.columnAt( 1) );
System.out.println( Matrix.fromString( test.toString() ));
}
}
class NoSuchLabelException extends Exception
{
public NoSuchLabelException()
{
super();
}
public NoSuchLabelException( String message )
{
super( message );
}
}
