Transcript Powerpoint Slides

CS 180
Recitation
8 / {30, 31} / 2007
Announcements
• Project 1 is out
– Due 9/5 @ 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
* @param 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”;
}
}