For Loops & Iterators CSC 171 FALL 2001 LECTURE 7

History: Vannevar Bush Vannevar Bush, MIT, built a large-scale differential analyzer with the additional capabilities of integration and differentiation. Funded by the Rockefeller Foundation, the differential analyzer was perhaps the largest computational device in the world in 1930

While loop

While loop Code int year = 0 ; While (year<=20){ balance += balance * interest; year++; }

For loop

For loop Code for (int year = 1;year<=20;year++){ balance += balance * interest; }

For Loop Initialization Test Body Increment for(initialzation;test;increment){ //Body }

Nested Loops Sometimes, we want to perform 2D operations Tables – Addition – Multiplication – Interest rates

Multiplication Table What is the output? int size = 5; // DON’T HARDCODE NUMS for(int i = 0 ; i<size;i++) { for(int j = 0 ; j<size;j++) { System.out.println(String.toString(i*j)); }

Multiplication Table Fixed int size = 5; for(int i = 0 ; i<size;i++) { for(int j = 0 ; j<size;j++) { System.out.print(String.toString(i*j) + “ “); } System.out.println(); }

Enumerations Integers are nice, because we always have a clear idea of what the next one is. But sometimes, we have an orderd set or list of things that aren’t numbers – {Hearts, Spades, Diamonds, Clubs} – {Bob, Carol, Ted, Alice} We would like to go through them one at a time

public interface Enumeration An object that implements the Enumeration interface generates a series of elements, one at a time. Successive calls to the nextElement method return successive elements of the series. For example, to print all elements of a vector v:

General Case Enumeration e = v.elements() ; while(e.hasMoreElements()) { System.out.println(e.nextElement()); }

Our Fave: StringTokenizer A String Tokenizer breaks strings up into tokens (surprize!) String “Hello CSC 171, How are you” Tokens: – “Hello”,“CSC”,”171,”,”How”,”are”,”you” StringTokenizer tokenizer = new StringTokenizer(inputLine);

String Tokenizer import java.util.StringTokenizer; public class Split { public static void main(String[] args) { ConsoleReader console = new ConsoleReader(System.in); boolean done = false; while (!done) { String inputLine = console.readLine(); if (inputLine == null) done = true; else { // break input line into words

String Tokeizer II StringTokenizer tokenizer = new StringTokenizer(inputLine); while (tokenizer.hasMoreTokens()) { // print each word String word = tokenizer.nextToken(); System.out.println(word); }

The switch statement A sequence of if/else that compares a single integer against constants can be implemented as a switch statement Consider the problem of naming digits 1 -> “one” 2 -> “two” …. 9 – “nine” Exercise – Write : public String digit2name(int n)

If solution public String digit2name(int n) { String name; if (n == 1) name = “one”; else if (n == 2) name = “two”; else if (n == 3) name = “three”; // etc... else if (n == 9) name = “nine”; else name = “”; return name; }

switch solution public String digit2name(int n) { String name; switch(n) { case 1: name = “one”; break; // check your breaks! case 2: name = “two”; break; // etc case 9: name = “nine”; break; default: name= “”; } return name; }

Constructor & Accesor Methods In order to prevent inadvertent (buggy) changes to an object, we want to limit access to the object’s data

Some instance varriables public class Student { public String studentName; public int studentNumber; }

Usage Student s1 = new Student(); s1.studentName = "Holly Yashi"; s1.studentNumber = ;

Control access with a constructor public class Student { private String studentName; private int studentNumber; public Student(String name; int number) studentName=name; studentNumber = number; }

Control access with accessors public class Student { private String studentName; private int studentNumber; public Student(String name; int number) studentName=name; studentNumber = number; } public String getname() { return studentName;} public int getnumber(){return studentNumber;} }

Usage Student s1 = new Student(“Holly Yashi”, ); System.out.println( s1.getname() + “’s student number is :” + s1.getnumber); // allows setting at construction time only