CS 180 Recitation 8 / {30, 31} / 2007

Announcements Project 1 is out –Due 10:00pm –Start early! –Use the newsgroup for your questions –LWSN B146 Lab help hours 7-10pm Monday through Wednesday

Naming Conventions Methods and variables begin with lower case int age, aMultipleWordVariable, another_multiple_word_variable; public void method() { } public void aMultipleWordMethod() { } Classes should begin with upper case public class MyClass { } Names should be descriptive for clarity and understanding No identifier can start with number Java is case sensitive aGe, Age, agE, AgE are all different in Java

Coding Conventions Code should be organized in a clean and clear fashion so that it is easy to read Tabs and whitespace do not change your code –Use them to cleanly space out your code –Don’t leave too much white space around – find a balance (ex: don’t double space lines of code)

Bad Code (My eyes! My eyes!) public class veRybAdpRogramMINgSTYLe { String NONdESCrIPTVariaBL_Ename; public String GEtS____tuFF () { return NONdESCrIPTVariaBL_Ename; } }

Good Code (Ah… much better!) public class Name { String name; public String getName() { return name; }

Comments Used to document your code Help remind you what variables or methods do/represent (a good name helps as well) Comment classes, class variables, and methods to describe what they are and what they do // a single line comment can use double slashes /* or you can do the multi-line style as well */ /* multi-line comments look like this */ /** * javascript comments look like this paramName our parameter */

String A Java class (we will discuss classes and objects in more detail later) A sequence of 0 or more characters including the 26 letters, digits 0-9, punctuation marks, and whitespaces Declaration – can use constructor String str = new String(“I love my TA!!!”); String str = “I love my TA!!!”; Use length() method to determine number of characters in the string String str = “I love my TA!!!”;// str.length() returns 15 Indexing characters starts at 0 –Starting indexing at 0 will be seen again when we study arrays) –Therefore, the characters are at indices 0…str.length()-1

String Substring – method used to grab a portion of the string –First index – the beginning character –Last index – the character after the last taken one (if none specified, go to end of string) String str = “myString!!!”; String str2 = str.substring(0,str.length()); // “myString!!!” String str3 = str.substring(3,5); // “tr” String str4 = str.substring(3); // “tring!!!”

Other Common Methods int indexOf(char) –Returns the first index of the character argument in the String, -1 if the character does not exist in the String char charAt(int) –Returns the character at the integer argument index in the String; an exception is thrown if the index is invalid Concatenation (+) –Combine two Strings together Many more methods – consult API

Dates Date class –From java.util package –Use toString method to print out the date toString is implicitly called for you SimpleDateFormat class –From java.text package –Used to format dates SimpleDateFormat sdf = new SimpleDateFormat(“MM/dd/yy”);

User Input Scanner –A java provided class in the java.util library –Many uses Input and parsing –Keyboard –Files (later in the semester) –Strings JOptionPane –A java provided class in the javax.swing library –Provides many methods to generate windows Messages Input

Two Sample Programs import java.util.Scanner; public class SampleProgram { public static void main(String[] args) { Scanner input = new Scanner (System.in); System.out.print(“Enter a word: “); String word = input.next(); System.out.println(“Your word is “ + word.length() + “ letters long.”); } import javax.swing.JOptionPane; public class SampleProgram { public static void main(String[] args) { String word = JOptionPane.showInputDialog(null, “Enter a word:”); JOptionPane.showMessageDialog(null, “Your word is “ + word.length() + “ letters long.”); }

Pig Latin! import java.util.Scanner; public class PigLatinTranslator { public static void main(String[] args) { PigLatinTranslator plt = new PigLatinTranslator(); Scanner input = new Scanner (System.in); System.out.print(“Enter a word to translate: “); String word = input.next(); System.out.println(word + “in pig latin is “ + plt.translate() + “.”); } // a very naïve translator public String translate(String s) { return s.substring(1) + s.charAt(0) + “ay”; }