1. Introduction to Computer Science and Object-Oriented Programming
Week 6

2. Tonight
Lab 2
Strings
Simple Input
Week 6

3. Strings Vital to solving problems
A series of 0 or more characters such as “Hello, World!” H e l o , W r d ! 1 2 3 4 5 6 7 8 9 10 11 12
Any letter, digit, punctuation mark, etc.
Strings have a length (the number of characters)
The characters in a String have positions starting at 0
Week 6

4. What Characters Java can represent a large number of characters
Accommodate many languages
Week 6

5. The Empty String In Java, a string can have no characters!
It’s length is zero
Also called the null string
It is represented by the literal constant ““ (two consecutive double quotes)
Turns out to be very useful
Week 6

6. What’s the difference between
Question
What’s the difference between
““ and “ “
Week 6

7. Noteworthy String is not a primitive type it’s a class (with methods)
But
is has a symbolic operator - the +
you don’t need a new to create String objects
Week 6

8. String Operator What is output? String firstName = “Rob”;
String lastName = “Collins”;
System.out.print(“Student’s name is: ”);
System.out.println(firstName + “ ” + lastName
+ “: Age ” );
What is output?
Week 6

9. String Methods String length Access a substring
String greeting = “Hello!”;
System.out.println(“Greeting size is ”
+ greeting.length());
Access a substring
String itemCode = “1998FXCAUS”;
String stateField = itemCode.substring(6, 8);
String countryField = itemCode.substring(8);
Manipulating characters:
String alpha = “abcdefg”;
char firstChar = alpha.charAt(0);
char lastChar = alpha.charAt(alpha.length() – 1);
int position = alpha.indexOf(‘c’);
String bigAlpha = alpha.toUpperCase();
For string positions, start counting at 0
Week 6

10. String Methods Using the substring method substring(start, pastEnd)
picks out the characters from the start position
up to, but not including the character at pastEnd So
substring(7,12) refers to “World” H e l o , W r d ! 1 2 3 4 5 6 7 8 9 10 11 12
Week 6

11. String Methods Using the substring method substring(start)
picks out the characters from the start position
thru the end of the string So
substring(7) refers to “World!” H e l o , W r d ! 1 2 3 4 5 6 7 8 9 10 11 12
Week 6

12. Question
String itemCode = “1998FXCAUS”;
String stateField = itemCode.substring(6, 8);
String countryField = itemCode.substring(8);
What values are assigned to stateField and countryField?
Is the value of itemCode changed? H e l o , W r d ! 1 2 3 4 5 6 7 8 9 10 11 12
Week 6

13. String Methods Using other String methods H e l o , W r d !
String alpha = “abcdefg”;
int position = alpha.indexOf(‘c’);
String bigAlpha = alpha.toUpperCase(); H e l o , W r d ! 1 2 3 4 5 6 7 8 9 10 11 12
Week 6

14. Converting String to a Number
Use Integer and Double classes
if a string is a proper representation of number
use the parseInt, parseDouble methods
String year = “2010”;
String width = “22.5”;
int numYear = Integer.parseInt(year);
double numWidth = Double.parseDouble(width);
Week 6

15. Getting Input So far we have worked with values stored them
calculated new values from exising values
output them
Now we learn a simple way to get input from the keyboard (the console in BlueJ)
Week 6

16. The Scanner class reads input
Create a Scanner object
Using System.in a a parameter
You need do this only once
Scanner input = new Scanner(System.in);
When you want input, prompt the user to enter it
System.out.print(“Enter menu choice (1-5): ”);
Read in using correct method (using “input” object):
int menuChoice = input.nextInt(); // reads integer
// waits until user hits <Enter> key
Week 6

17. The Scanner class reads input
Read a value - using the correct method
int menuChoice = input.nextInt();
nextDouble reads a double
nextLine reads a line (until user hits Enter)
nextWord reads a word (until any white space)
Week 6

18. Scanner Example p. 166 of Big Java 01: import java.util.Scanner; 02:
03: /**
04: This program simulates a transaction in which a user pays for an item
05: and receives change.
06: */
07: public class CashRegisterSimulator
08: {
09: public static void main(String[] args)
10: {
11: Scanner in = new Scanner(System.in);
12:
13: CashRegister register = new CashRegister();
14:
15: System.out.print("Enter price: ");
16: double price = in.nextDouble();
17: register.recordPurchase(price);
18:
19: System.out.print("Enter dollars: ");
20: int dollars = in.nextInt();
p. 166
of Big Java
Week 6

19. Scanner Example Output:
Enter price: Enter dollars: 10 Enter quarters: 2 Enter dimes: 1 Enter nickels: 0 Enter pennies: 0 Your change: is 3.05
Week 6