CSCI S-1Section 9

Coming Soon

• Problem Set Four (72 + 5/15 points)– Tuesday, July 21, 17:00 EST

• Problem Set Five (30 + 5 points)– Friday, July 24, 17:00 EST

• Term Project Proposal– ALSO Friday, July 24, 17:00 EST

Java Documentation

java.sun.com/j2se/1.5.0/docs/api/

Arrays

• fixed-size container• direct access to each element • 0-based index• all objects of the same type

Creating Arrays

• double [ ] temps = new double [ 5 ];• int [ ] numbers = new int [10];• boolean [ ] flags = new boolean [20];• String [100] names = new String [100];

Filling Arrays

//temps [0] is the first element in the array of length 5

Filling Arrays

//temps [0] is the first element in the array of length 5

for ( int i = 0; I < 5; i++ )temps[i] = 98 + Math.random() * 6;

Filling Arrays

//temps [0] is the first element in the array of length 5

for ( int i = 0; I < temps.length; i++ )temps[i] = 98 + Math.random() * 6;

Filling Arrays

/* print out temperature and index when temperature is greater than 104 */

Filling Arrays

/* print out temperature and index when temperature is greater than 104 */

for ( int i = 0; I < temps.length; i++ )if ( temps[i] > 104 )

System.out.println(“temps: “ + temps[i] + “ at index: “ + i);

Array Methods

System.out.println(tems); //don’t

import java.util.Arrays;System.out.println(Arrays.toString(temps));

Quick Snips• First item in array A• Last item in array A• Make A 100 strings long

• Length of first string in A• A has strings in even

positions and doubles in odd positions

• Append one additional element to end of array

• A [0]• A [ A.length - 1 ]• String [] A = new String

[100];• A [0].length()• no can do

• no can do

Compare Arrays

boolean isEqualTo( int [] arr1, int [] arr2)

public static void main(String[] args) { int [] arr1 = {13, 14, 15}; int [] arr2 = {13, 14, 16, 17}; System.out.println(isEqualTo(arr1, arr2)); }

Compare Arrays

private static boolean isEqualTo(int [] a1, int [] a2) {

}}

Compare Arrays

private static boolean isEqualTo(int [] a1, int [] a2) { if (a1.length != a2.length) return false; else { for (int i=0; i<a1.length; i++) if (a1[i]!=a2[i]) return false; return true; }}

Command-Line Arguments

//print out command-line argumentspublic static void main(String[] args) {

}

Command-Line Arguments

//print out command-line argumentspublic static void main(String[] args) {

for (int i = 0; i < args.length; i++) System.out.println(args[i]);}

Command-Line Arguments

// convert first command-line arg to int using Integer.parseInt()public static void main(String [] args) {

}

Command-Line Arguments

// convert first command-line arg to int using Integer.parseInt()public static void main(String [] args) {

if (args.length != 0) int firstArg = Integer.parseInt(args[0]) ;

}

Exceptions: Try & Catchpublic static void main(String [] args) { if (args.length != 0) { try { int i= Integer.parseInt(args[0]) ; } catch (NumberFormatException e) { System.exit(1); } }}

Recursion

What is 2 to the power of 5?2 * 2 * 2 * 2 * 2

What is 2 to the power of 4?2 * 2 * 2 * 2

In other words,

45 222

Recursion

//Does this work?private static int power(int a, int b){

return (a * power(a, b-1)); }

Recursion

//Add the “base case"private static int power(int a, int b){

if (b==0) return 1;return (a * power(a, b-1));

}