8/9: 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 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 0col 1 row 031 row 120 row 268 row 375

Multiple-Subscripted Arrays Another way to remember: “first the row, then the position” int sample [] [] = { {3,1},{2,0},{6,8},{7,5} }; col 0col 1 row 031 row 120 row 268 row 375

Multiple-Subscripted Arrays EX: int sample[] [] = new int [ 4 ] [ 2 ]; sample [3][0] = 7 sample [1][1] = 0 sample [0][1] = ? sample [2][0] = ? col 0col 1 row 031 row 120 row 268 row 375

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 Tomorrow: Final Exam –Correct the code –Create the code –What’s the output –Full period (1 ½ hrs.)