1. Introduction to Computer Science and Object-Oriented Programming
Week 6
Introduction to Computer Science and Object-Oriented Programming
COMP 111
George Basham

2. Week 6 Topics
Strings
Reading Input

3. Strings
A string is a series of characters such as “Hello, World!”
Strings are delimited by (enclosed within) quotation marks
Creating a string object does not require the new operator: String msg = “Hello, World!”;
The length of the example string above is 13 and can be determined via a call to the length method: System.out.println(msg.length());

4. The + operator is used to concatenate strings (put them together):
Strings Cont.
The + operator is used to concatenate strings (put them together):
String a = “Agent”;
int n = 7;
String bond = a + n;
Note that the integer value n is converted to a string
Use concatenation to simplify expressions: System.out.println(“Total is ” + total);

5. Strings Cont.
If a string contains digits of a number, you can use the Integer.parseInt or the Double.parseDouble method to obtain the number value
int count = Integer.parseInt(input);
double price = Double.parseDouble(input);

6. Strings Cont.
Use the substring method to extract a part of a string: s.substring(start, pastEnd)
You specify the position you want to start at, and the position one past the position you want to end at
String msg = “Hello, World!”;
String sub = msg.substring(0, 5);
// sub is “Hello”

7. 6.1.1 Strings Cont. String msg = “Hello, World!”;
String sub = msg.substring(7, 12);
// sub is “World”
String sub = msg.substring(7); // World!
Above copies from start pos to end H e l o , W r d ! 1 2 3 4 5 6 7 8 9 10 11 12

8. Reading Input
In Java version 5.0, a Scanner class was added that lets you read keyboard input in a convenient manner
To construct a Scanner object, simply pass the System.in object to the Scanner constructor: Scanner in = new Scanner(System.in);
Once you have a scanner, use nextInt or nextDouble method to read a whole number or a floating point number.

9. Reading Input Cont.
Scanner in = new Scanner(System.in);
System.out.print(“Enter Quantity: ”);
int quantity = in.nextInt();
System.out.print(“Enter Price: ”);
double price = in.nextDouble();

10. Reading Input Cont.
nextLine() gets all text including spaces, next() gets a word (token) as soon as it comes to a white space (space, end of line, tab)
System.out.print(“Enter City: ”);
String city = in.nextLine();
System.out.print(“Enter state code: ”);
String state = in.next();
import java.util.Scanner;

11. Reading Input Cont.
An alternative to using a Scanner class and the console is to have a dialog box.
String input = JOptionPane.showInputDialog(“First number: “);
Convert the String to a number if necessary as previously discussed.
Add this line to the end of your main method:
System.exit(0);
import javax.swing.JOptionPane;

13. Reference: Big Java 4th Edition by Cay Horstmann
Strings (section 4.5 in Big Java)
Reading Input (section 4.6 in Big Java)