1. CSS 161 Fundamentals of Computing Introduction to Computers & Java
Joe McCarthy
CSS 161: Fundamentals of Computing

2. CSS 161: Fundamentals of Computing
Outline
Updates / reminder
Recap: Intro to Java
Today:
Chapter 1: Assignments, expressions, data types
Chapter 2: Console Input & Output (I/O)
Next time: Lab 2 (UW1-120)
CSS 161: Fundamentals of Computing

3. CSS 161: Fundamentals of Computing
Updates / Reminder
UW1-120
Mondays (“lectures”) & Fridays (labs)
Wednesdays: here (UW2-031)
Modified office hours
MW 10:15-10:45 [no change]
MW 7:45-8:15 (UW1-220)
TTh 7:15-7:45pm [no change]
& by appointment
Lab 1
Due Friday, Oct 7, 11am
Assignment 1
Due Monday, Oct 10, 11am
CSS 161: Fundamentals of Computing

4. CSS 161: Fundamentals of Computing
Recap: Intro to Java
Class
Method
main()
Identifier
Reserved word
Variable
Declaration
Assignment
Operator
System.out.println()
Output:
= 30
CSS 161: Fundamentals of Computing

5. CSS 161: Fundamentals of Computing

6. Assignments & Expressions
Syntax:
variable = expression
Semantics:
Evaluate expression, assign value to variable
Expression:
Constant (1, 1.23, 3.45e6, ‘a’, “css161”, true, false)
final static int COURSENUMBER = 161;
Variable (num2)
expression operator expression
Operators:
*, /, %
+, - …
CSS 161: Fundamentals of Computing

7. Operators & Precedence
Can use parentheses to change precedence
1 + 2 * 3
(1 + 2) * 3
CSS 161: Fundamentals of Computing

8. CSS 161: Fundamentals of Computing

9. Shorthand assignments
Example:
Equivalent To:
count += 2;
count = count + 2;
sum -= discount;
sum = sum – discount;
bonus *= 2;
bonus = bonus * 2;
time /=
rushFactor;
time =
time / rushFactor;
change %= 100;
change = change % 100;
amount *=
count1 + count2;
amount = amount * (count1 + count2);
CSS 161: Fundamentals of Computing

10. Increment & Decrement Operators
Syntax:
variable++ | ++variable | variable-- | --variable
Semantics:
Set variable to next / previous value
Examples
int num1 = 1; char char1 = ‘B’;
num1++;
char1--;
Precedence: increment/decrement before/after use
2*(num1++)  2
2*(++num1)  4
CSS 161: Fundamentals of Computing

11. Assignment Compatibility
byteshortintlongfloatdouble
char
CSS 161: Fundamentals of Computing

12. Type casting & coercion
Syntax:
variable = (type) expression
Semantics
Convert expression to type, assign value to variable
Only allowed if expression type is compatible with variable type
Type coercion:
Automatic type casting: int  float  double
Examples
short num3 = (short) ‘A’;
int num4 = (int) 1.9;
double num5 = 123; // coercion
int num6 = 1.23; // error
CSS 161: Fundamentals of Computing

13. CSS 161: Fundamentals of Computing
Console Input & Output
System.out
A Java object associated with the console (screen)
print(), println()
Methods associated with the System.out object
Syntax:
System.out.print(expression)
System.out.println([expression])
Semantics:
Evaluate expression, output its value
println:
expression is optional (hence the square brackets [])
output a carriage return / line feed (newline) at end of line
CSS 161: Fundamentals of Computing

14. Formatted output: printf
Syntax:
System.out.printf(format[,expression]*)
Semantics:
Use format string to output expression(s)
Examples:
System.out.printf(“Hello”);
System.out.printf(“Hello%n”);
System.out.printf(“%5.1f”, 1.25);
System.out.printf(“%-5.1f”, 1.25);
System.out.printf(“$.2f”, 1.2);
CSS 161: Fundamentals of Computing

15. Format string specifiers
CSS 161: Fundamentals of Computing

16. Console input: Scanner class
Not built-in, have to import
import java.util.Scanner;
Next: create an instance of the class
Syntax:
classname variable = new classname([args])
Semantics:
Create an instance of classname, initialize it with args, assign instance to variable
Example:
Scanner keyboard = new Scanner(System.in);
Create an instance of the Scanner class (in java.util package)
Initialize it to accept input from the system console (System.in)
Assign it to keyboard (NB: keyboard not a reserved word)
CSS 161: Fundamentals of Computing

17. Console Input Using the Scanner Class
The method nextInt reads one int value typed in at the keyboard and assigns it to a variable:
int numberOfPods = keyboard.nextInt();
The method nextDouble reads one double value typed in at the keyboard and assigns it to a variable:
double d1 = keyboard.nextDouble();
Multiple inputs must be separated by whitespace and read by multiple invocations of the appropriate method
Whitespace is any string of characters, such as blank spaces, tabs, and line breaks that print out as white space
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

18. Console Input Using the Scanner Class
The method next reads one string of non-whitespace characters delimited by whitespace characters such as blanks or the beginning or end of a line
Given the code
String word1 = keyboard.next();
String word2 = keyboard.next();
and the input line
jelly beans
The value of word1 would be jelly, and the value of word2 would be beans
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

19. Console Input Using the Scanner Class
The method nextLine reads an entire line of keyboard input
The code,
String line = keyboard.nextLine();
reads in an entire line and places the string that is read into the variable line
The end of an input line is indicated by the escape sequence '\n'
This is the character input when the Enter key is pressed
On the screen it is indicated by the ending of one line and the beginning of the next line
When nextLine reads a line of text, it reads the '\n' character, so the next reading of input begins on the next line
However, the '\n' does not become part of the string value returned (e.g., the string named by the variable line above does not end with the '\n' character)
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

20. Keyboard Input Demonstration (Part 1 of 2)
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21. Keyboard Input Demonstration (Part 2 of 2)
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22. Another Keyboard Input Demonstration (Part 1 of 3)
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23. Another Keyboard Input Demonstration (Part 2 of 3)
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24. Another Keyboard Input Demonstration (Part 3 of 3)
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25. Pitfall: Dealing with the Line Terminator, '\n'
The method nextLine of the class Scanner reads the remainder of a line of text starting wherever the last keyboard reading left off
This can cause problems when combining it with different methods for reading from the keyboard such as nextInt
Given the code,
Scanner keyboard = new Scanner(System.in);
int n = keyboard.nextInt();
String s1 = keyboard.nextLine();
String s2 = keyboard.nextLine();
and the input, 2
Heads are better than
1 head.
what are the values of n, s1, and s2?
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

26. Pitfall: Dealing with the Line Terminator, '\n'
Given the code and input on the previous slide
n will be equal to "2",
s1 will be equal to "", and
s2 will be equal to "heads are better than"
If the following results were desired instead
n equal to "2",
s1 equal to "heads are better than", and
s2 equal to "1 head"
then an extra invocation of nextLine would be needed to get rid of the end of line character ('\n')
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

27. Methods in the Class Scanner (Part 1 of 3)
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28. Methods in the Class Scanner (Part 2 of 3)
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29. Methods in the Class Scanner (Part 3 of 3)
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

30. Java Documentation for Scanner
CSS 161: Fundamentals of Computing

31. Programming Tip: Prompt for Input
A program should always prompt the user when he or she needs to input some data:
System.out.println(
"Enter the number of pods followed by");
"the number of peas in a pod:");
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

32. Programming Tip: Echo Input
Always echo all input that a program receives from the keyboard
In this way a user can check that he or she has entered the input correctly
Even though the input is automatically displayed as the user enters it, echoing the input may expose subtle errors (such as entering the letter "O" instead of a zero)
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

33. Self-Service Checkout Line (Part 1 of 2)
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34. Self-Service Checkout Line (Part 2 of 2)
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35. The Empty String
A string can have any number of characters, including zero characters
"" is the empty string
When a program executes the nextLine method to read a line of text, and the user types nothing on the line but presses the Enter key, then the nextLine Method reads the empty string
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

36. Other Input Delimiters
The delimiters that separate keyboard input can be changed when using the Scanner class
For example, the following code could be used to create a Scanner object and change the delimiter from whitespace to "##"
Scanner keyboard2 = new Scanner(System.in);
Keyboard2.useDelimiter("##");
After invocation of the useDelimiter method, "##" and not whitespace will be the only input delimiter for the input object keyboard2
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

37. Changing the Input Delimiter (Part 1 of 3)
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38. Changing the Input Delimiter (Part 2 of 3)
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39. Changing the Input Delimiter (Part 3 of 3)
Copyright © 2010 Pearson Addison-Wesley. All rights reserved.

40. Next Time Lab 2 (UW1-120) Don’t forget: Lab 1 due Friday, 11am
Assignment 1 due Monday, 11am