1. Announcements & Review
Last Time:
int, boolean
some operations
boolean logic
if-then-else!
Announcements
Friday
I’m away, Katie Coons will teach
Lab 1 Due
Thursday 10pm
Use turnin
1 file per pair
Lecture 6: String Objects and Input

2. Lecture 6: String Objects and Input
Today
Clairfy float verses double
Finish if-then-else example
More basic program elements
Objects versus values
Strings & their operators
Input
Using the Scanner class
Lecture 6: String Objects and Input

3. Lecture 6: String Objects and Input
Values versus objects
Numbers
Have values but they do not have behaviors
Objects
Have attributes and behaviors
System.out - References an OutputStream
Attribute: monitor
Behaviors: printing
System.in: References an InputStream
Attribute: keyboard
Behaviors: reading
Java treats object variables differently. Although an object variable is the symbolic name for a memory location being used by the program, the memory location for an object variable does not store a value of that object type. Instead the value in the memory location tells the program where to find a value (object) of that type.
We say that an object variable references or points to an object of the object type. Thus, a String variable references a memory location that holds a value of type String. Similarly, a BufferedReader variable references a memory location holding a BufferedReader value.
Lecture 6: String Objects and Input

4. Lecture 6: String Objects and Input
Consider
String a = "excellence";
String b = a;
What is the representation?
Lecture 6: String Objects and Input

5. Lecture 6: String Objects and Input
Examples
Consider
String a = "excellence";
String b = a;
What is the representation? a
"excellence" b
Lecture 6: String Objects and Input

6. Uninitialized versus null
Consider
String dayOfWeek;
Scanner inStream;
What is the representation?
Lecture 6: String Objects and Input

7. Uninitialized versus null
Consider
String dayOfWeek;
Scanner inStream;
What is the representation?
dayOfWeek -
inStream -
Lecture 6: String Objects and Input

8. Uninitialized versus null
Consider
String fontName = null;
Scanner fileStream = null;
What is the representation?
Lecture 6: String Objects and Input

9. Uninitialized versus null
Consider
String fontName = null;
Scanner fileStream = null;
What is the representation?
fontName
null
fileStream
null
Lecture 6: String Objects and Input

10. Lecture 6: String Objects and Input
Assignment
Consider
String word1 = "luminous";
String word2 = "graceful";
->
word1 = word2;
Representation at ->
word1
"luminous"
word2
"graceful"
Lecture 6: String Objects and Input

11. Lecture 6: String Objects and Input
Assignment
Consider
String word1 = "luminous";
String word2 = "graceful";
word1 = word2;
->
After assignment
word1
word2
"graceful"
Lecture 6: String Objects and Input

12. String representation
Consider
String alphabet = "abcdefghijklmnopqrstuvwxyz";
Standard shorthand representation
Truer representation
alphabet
"abcdefghijklmnopqrstuvwxyz"
Another useful String member method is charAt(). This method expects a single index as its parameter and returns the value of the character at that position in its String. While such behavior seems relatively natural given the method name and its parameter, what is not natural is that in Java, as in several other programming languages, the first character of a String is located at index 0.
alphabet a b c d e f g h i j k l m n o p q r s t u v w y z
Lecture 6: String Objects and Input

13. Lecture 6: String Objects and Input
Some String Methods
// a string objects
String alphabet = "abcdefghijklmnopqrstuvwxyz";
// operations on string objects
char c1 = alphabet.charAt(9);
int position = alphabet.indexOf(“e”);
String ab = alphabet.substring(0, 2);
String moreLetters = ab.concat(alphabet);
boolean sameStr = moreLetters.equals(ab);
…. lots more … see pgs in Cohoon & Davidson or Javadoc (google it!)
Lecture 6: String Objects and Input

14. Lecture 6: String Objects and Input
Example String Method
String alphabet = "abcdefghijklmnopqrstuvwxyz";
char c1 = alphabet.charAt(9);
char c2 = alphabet.charAt(2);
int i1 = alphabet.indexOf(“de”);
What are the values of c1, c2, and c3? Why?
Lecture 6: String Objects and Input

15. Lecture 6: String Objects and Input
BlueJ Examples
Lecture 6: String Objects and Input

16. Reading Input Features
// Scanner is an “extra” Java class, so we
// need to tell the compiler where to find it
import java.util.*
// allocates an object of class Scanner
Scanner stdin = new Scanner(System.in);
String name = stdin.next();
int age = stdin.nextInt();
double commuteDistance = stdin.nextDouble();
boolean parent = stdin.nextBoolean();
// peeking to make sure the format is right
// we will use these in Lecture 8
boolean isString = stdin.hasNext();
boolean isInt = stdin.hasNextInt();
boolean isDouble = stdin.hasNextDouble();
boolean isBoolean = stdin.hasNextBoolean();
Lecture 6: String Objects and Input

17. Lecture 6: String Objects and Input
Reading Input Example
// Scanner is an “extra” Java class, so we
// need to tell the compiler where to find it
import java.util.*
// allocates an object of class Scanner
Scanner stdin = new Scanner(System.in);
System.out.print("Enter a word: ");
String word = stdin.next();
int wordLength = word.length();
System.out.println("Word " + word + " has length ” + wordLength + ".");
Lecture 6: String Objects and Input

18. Lecture 6: String Objects and Input
BlueJ Examples
Lecture 6: String Objects and Input

19. Lecture 6: String Objects and Input
More Questions?
Lecture 6: String Objects and Input