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11/27: Multiple-Subscripted Arrays
• About BinarySearch.java
• Multiple-Subscripted Arrays
• Program of the Day
BinarySearch.java pt.1
//fig. 7.13: BinarySearch.java: binary search of an array
import java.awt.*;
import java.awt.event.*;
import java.text.*;
import javax.swing.*;
public class BinarySearch extends JApplet
implements ActionListener {
JLabel enterLabel, resultLabel;
JTextField enter, result;
JTextArea output;
int a[];
String display = "";
BinarySearch.java pt.2
public void init ()
{
Container c = getContentPane();
c.setLayout ( new FlowLayout() );
enterLabel = new JLabel ( "Enter key" );
c.add( enterLabel );
enter = new JTextField( 5 );
enter.addActionListener( this );
c.add( enter );
resultLabel = new JLabel ( "Result" );
c.add( resultLabel );
BinarySearch.java pt.3
result = new JTextField( 22 );
result.setEditable( false );
c.add( result );
output = new JTextArea( 6, 60 );
output.setFont(new Font("Courier",Font.PLAIN,12 ) );
c.add( output );
//create array and fill it with even numbers 0-28
a = new int[ 15 ];
}
for ( int i = 0; i < a.length; i++ )
a[ i ] = 2 * i;
BinarySearch.java pt.4
public void actionPerformed ( ActionEvent e )
{
String searchKey = e.getActionCommand();
//initialize display string for new search
display = "Portions of array searched\n";
//perform the binary search
int element = binarySearch ( a, Integer.parseInt (
searchKey ) );
output.setText( display );
}
if ( element != -1 )
result.setText( "Found it in slot " + element );
else
result.setText( "Value not found" );
BinarySearch.java pt.5
//binary search method
public int binarySearch ( int array[], int key )
{
int low = 0;
//low subscript
int high = array.length - 1;//high subscript
int middle;
//middle subscript
while ( low <= high ) {
middle = ( low + high ) / 2;
//The next line displays the part of the array still
//available for searching through for the key.
buildOutput ( low, middle, high );
BinarySearch.java pt.6
if ( key == array[middle] ) //a match
return middle;
else if ( key < array[middle] )
high = middle - 1; //search lower array
else
low = middle + 1;
}
}
return -1;
//searchKey not found
BinarySearch.java pt.7
//build 1 row of output w/ part of the array being processed.
void buildOutput ( int low, int mid, int high )
{
DecimalFormat twoDigits = new DecimalFormat ( "00" );
for ( int i = 0; i < a.length; i++ ) {
if ( i < low || i > high )
display += " ";
else if ( i == mid ) //mark middle element in output
display += twoDigits.format ( a [ i ] ) + "* ";
else
display += twoDigits.format ( a [ i ] ) + " ";
}
}
}
display += "\n";
Multiple-Subscripted Arrays
• Used to represent a table of values, not just a row.
• By convention, the 1st number = row number,
and the 2nd number = column number.
• EX: int sample[] [] = new int [ 4 ] [ 2 ];
might have values like this:
col 0
col 1
row 0
3
1
row 1
2
0
row 2
6
8
row 3
7
5
Multiple-Subscripted Arrays
• Another way to remember: “first the row, then the
position”
• int sample [] [] = { {3,1},{2,0},{6,8},{7,5} };
col 0
col 1
row 0
3
1
row 1
2
0
row 2
6
8
row 3
7
5
Multiple-Subscripted Arrays
• EX: int sample[] [] = new int [ 4 ] [ 2 ];
col 0
col 1
row 0
3
1
row 1
2
0
row 2
6
8
row 3
7
5
sample [3][0] = 7
sample [1][1] = 0
sample [0][1] = ?
sample [2][0] = ?
Multiple-Subscripted Arrays
• But how do you use them?
• Think of them as arrays of arrays (lists of lists).
for ( int i = 0; i < id.length; i++ ) {
for ( int j = 0; j < id[i].length ; j++ ){
g.drawString(“ “ + (id[ i ][ j ]),x,y);
}
}
see StringArray.java
Program of the Day
• pg. 297 DoubleArray.java
• Quiz #4 on Thursday: open-note, like usual
– What’s probably on it:
•
•
•
•
recursion,
method overloading,
scoping, and
arrays: everything but multiple-subscripted arrays.
– What’s NOT on it:
• multiple-subscripted arrays.