CSE 11 HW 2, 3 and 4 Posted in public and on web Deadlines HW 2 turnin: Wed Jan 22 interview: Saturday January 25.class files in public directory for HW 2 & 3 Do not need to turnin the HW if you take an interview before the turnin deadline

Copywrite 2003 Walter Savitch These slides are for the exclusive use of students in CSE 11 at UCSD, Winter quarter They may not be copied or used for any other purpose without the written permission of Walter Savitch.

Reading Cover approx. Chapters 1-5 so far. Next do Chapter 6, today, read all of it Chapter 10, sec Vectors Chapter 11 Recursion All needed for hw3-4

Inner Class Class defined within another class. Can be private and then local to the outer class. For now, we use it only to make a hw assignment into a single class for the turnin program. (Can make inner classes either public or private for this.)

You may need to make an inner class static public class Match { public static class Person { …. }//end Person …. }//end Match

Package A named collection of class. A library of classes. Can be stored in one directory and used in any directory.

Adding a class to a package package myLibrary; public class Sample {

Using a package import myLibrary; public class MyProgram {

Package Names and Directories Package name is a relative path name from a class path directory to the package directory. Uses dots rather than /, for example myPackages.CSE11.speciesStuff Class path is an environment variables of the operating system. How you set it depends on the operating system. Typically looks like: path; path; path; Be sure to include a dot for the current directory in your class path.

Class Path on sunpal setenv CLASSPATH.:/home/solaris/ieng9/cs11w/cs11wab/path1: /home/solaris/ieng9/cs11w/cs11wab/path2 Note dot at start Note the use of colons not semicolons

Class Path on sunpal setenv CLASSPATH ~/lib import iolib.savitchstuff.*; If SavitchIn.class is in ~/lib/iolib/savitchstuff Then it does not have to be in the same directory as your program or class.

Class Path on sunpal Must add the following to SavitchIn.java package iolib.savitchstuff; ~/lib should be on CLASSPATH SavitchIn.class must be in the directory ~/lib/iolib/savitchstuff Must add the following to your program import iolib.savitchstuff.*;

Arrays Give uniform names to a collection of variables all of the same type. Array type names: int[], double[], Species[] int[] a = new int[3]; declares 3 int variables named a[0], a[1], and a[2]

double[] temperature = new double[7]; int index; double sum, average; System.out.println("Enter 7 temps:"); sum = 0; for (index = 0; index < 7; index++) { temperature[index] = SavitchIn.readLineDouble( ); sum = sum + temperature[index]; } average = sum/7;

Java Arrays Indexes always start with 0 An array (as a whole) is an object Arrays check for index out of bounds Arrays know their size

Length Instance Variable String[] a = new String[10]; a.length has the value 10 a.length is read-only; You cannot change it.

Use of length for (index = 0; index < temperature.length; index++) { temperature[index] = SavitchIn.readLineDouble( ); sum = sum + temperature[index]; }

Array Instance Variables as Arguments Nothing new. If a is an array of doubles, the a[2] can be used just like any other variables of type double.

Entire Array as an Argument Array variables are reference variables, just like class objects. Array parameters are just like class parameters (Call-by-value for a reference.) Arrays know their size. One array type for all arrays with the same base type, e.g. double[] is the type for any array of doubles of any size.

Arrays Can Be Returned by a Method

public static double[] averageArray (int firstScore, int[] nextScore) { double[] temp = new double[nextScore.length]; int i; for (i = 0; i < temp.length; i++) temp[i] = average(firstScore, nextScore[i]); return temp; }

What is wrong? Species[] a = new Species[3]; a[0].readInput(); Error message “Null Pointer Exception” a[0] is a varaible of type Species, but is just a variable. It has no refernce to any object. Need a[0] = new Species();

Species[] a = new Species[3]; for (int i = 0; i < a.length; i++) a[i] = new Species(); a[0].readInput(); //OK a[1].readInput(); //OK a[2].readInput(); //OK

Multidimentional Arrays More than one index. Implemented as array of arrays Read on your own.

Recursion (Chapter 11) Recursive method == one that invokes itself Anything will compile. Need some care to get method to run OK. Read all of Chapter 11

writeVertical Example Static method ClassName.writeVertical(1234); Outputs

public static void writeVertical(int n) { if (n < 10) System.out.println(n); else //n is two or more digits long: { writeVertical(n/10); System.out.println(n%10); }

ClassName.writeVertcal(123); Equivalent to writeVertical(123/10); System.out.println(123%10); Equivalent to writeVertical(12); System.out.println(3); Equivalent to writeVertical(12/10); System.out.println(12%10); System.out.println(3);

writeVertical(12/10); System.out.println(12%10); System.out.println(3); Equivalent to writeVertical(1); System.out.println(2); System.out.println(3); Equivalent to System.out.println(1); System.out.println(2); System.out.println(3);

Stack Like a stack of paper Last-in/First-out Used to implement recursion

Successful Recursive Method Two cases Case with recursive calls Stopping case (Base case) with no recursive calls