Lecture An introduction to computer science using java (2nd Edition): Chapter 3 - S.N. Kamin, D. Mickunas, E. Reingold

Chapter 3

Fundamental Data Types of Java
Lecture Slides to Accompany

An Introduction to Computer Science
Using Java (2nd Edition)
by
S.N. Kamin, D. Mickunas, E. Reingold
 

 


Chapter Preview
In this chapter we will:
• discuss four important data types
–
–
–
–

integers
real numbers
strings
characters

• describe the process of developing and
debugging a Java program
 

 


Integers
• Numbers without fractional parts
3, 47, -12
• Variables can be used to store integers using
an assignment statement
int daysInWeek;
daysInWeek = 7;

• In general integer variables may be used any
place an integer literal can be
 

 


Reading Integers
import CSLib.*;
Inputbox in;
int i;
in = newInputBox();
in.setPrompt(“Enter an integer: “);
i = in.readInt();

 

 

Integer Arithmetic Operations
Symbol

Operation

+

Addition

45 + 5 = 50

-

Subtraction

657 – 57 = 600

*

Multiplication 7000 * 3 = 2100

/

Division

10 / 3 = 3

Remainder

10 % 3 = 1

%
 

Example

 


Precedence Rules
1. Evaluate all subexpressions in parentheses
2. Evaluate nested parentheses from the
inside out
3. In the absence of parentheses or within
parentheses
a. Evaluate *, /, or % before + or –
b. Evaluate sequences of *, /, and % operators
from left to right
c. Evaluate sequences of + and – operators from
left to right
 

 


Precedence Examples
• Example 1
6 + 37 % 8 / 5 is the same as
6 + ((37 % 8) / 5) =

6 + ( 5 / 5) = 7

• Example 2
6 + 37 % (8 / 5) =
6 + 37 % 1 =
6+0=6
 

 


Additional Integer Operators
• Self-assignment
temperature = temperature + 10;

• Increment
cent++;
equivalent to
cent = cent + 1;

• Decrement
cent--;
equivalent to
cent = cent - 1;
 

 


Initializers

• May be used to give variables initial values
int x = 5;
int y = 6;

• Can be written more concisely
int x = 5,
y = 6;

• Can use expressions on the right hand side
int x = 5,
y = x + 1;
 

 


Symbolic Constants
• Useful when you want a variable whose
value never changes
• Use the modifier final in its
declaration
• Example
final int US_Population = 278058881;

 

 


Real Numbers

• Numbers with fractional parts
3.14159, 7.12, 9.0, 0.5e001, -16.3e+002
• Declared using the type double
double pricePerPound = 3.99;
taxRate
= 0.05;
shippingCost = 5.55;

• The initialization part of the declaration is
optional
 

 


Real Arithmetic Operations
Symbol

 

Operation

Example

+

Addition

4.50e01 + 5.30e00 =
5.03e01

-

Subtraction

6.57e02 – 5.7oe01 =
6.00e02

*

Multiplication

7e02 * 3.0e00 =
2.1e04

/

Division

9.6e01 / 2e01 =
4.8e00

 


Reading Real Numbers
import CSLib.*;
Inputbox in;
double temp;
in = newInputBox();

in.setPrompt(“Enter a real number: “);
temp = in.readDouble();

 

 


 

 


Strings
• String is a class defined in the java.lang
package
• Unlike other Java classes String has literals and a
defined operation
• Examples
String prompt = “Enter an integer:”;
String t1 = “To be “,
t2 = “or not to be”;
out.print(t1 + t2);
Out.print(“Mass is “ + x * 2.2 + “ Kg”);

 

 

String Method Examples
OutputBox out = new OutputBox();
String s1 = “Here is a test string”;
out.println(s1.indexOf(“s”)); // prints 6
out.println(s1.indexOf(“x”)); // prints
-1
out.println(s1.length());
22

// prints

out.println(s1.substring(8,14));
// prints ‘a test’
 
 


 

 


Reading Strings
import CSLib.*;
Inputbox in;
String input;
in = newInputBox();
in.setPrompt(“Enter a real number: “);
input = in.readString();

 

 


Characters
• Any key you type on the keyboard generates
a character which may or may not be
displayed on the screen (e.g. nonprinting
characters)
• Characters are a primitive type in Java and
are not equivalent to strings
• Examples
char vitamin = ‘’A’,
chromosome = ‘’y’,
middleInitial = ‘’N’;
 

 


Important Literal Characters
‘A’, … ,‘Z’

Uppercase letters

‘a’, … ,‘z’

Lowercase letters

‘0’, … , ‘9’

Digits

‘.’,’,’,’!’,’”’,etc.

Punctuation Marks

‘ ’

Blank

‘\n’

New line

‘\t’

Tab

‘\\’

Backslash

‘\’’

Single Right Quote

 

 


Common Debugging Problems
• Misleading compiler error messages
– Syntax errors indicated on one-line may actually
reflect an error made on an earlier line

• Capitalization errors
– Java is case sensitive, identifier names must use
the same capitalization rules each time

• Logic Errors
– Program appears to run correctly, but on closer
inspection the wrong output is displayed
 

 


Limitations of Numeric Variables
• Unlike the integers mathematics the type int
is not infinitely large and it is possible to
compute a value incorrectly because the
value is too large to be stored in an int
variable storage location
• Unlike the real numbers in mathematics the
type double is not dense, it is not always
possible to test double expressions for
equality and obtain a correct result due to

rounding errors in representations
 

 


Mixing Numeric Data Types
• Java will automatically convert int expressions to
double values without loss of information
int i = 5;
double x = i + 10.5;
• To convert double expressions to int requires a
typecasting operation and truncation will occur
i = (int) (10.3 * x)

• To round-up instead of truncating add 0.5
i = (int) (10.3 * x + 0.5)

 

 


Mixed Mode Operations and
Strings
• It is important to remember that “13” and 13
are not the same
• Examples
out.println(“4” + “5”) // prints 45
out.println(“4” + 5)

// prints 45
out.println(4 + 5)
// prints 9

 

 


Characters as Integers
• It is legal to assign a char to an int variable
int i = ‘a’; // assigns 97 to i
• It is legal to assign an int to an char
variable
char c = 97; // assigns ‘a’ to c
• It is possible to perform arithmetic on char
variables
char ch = ‘a’;
ch = ch + 1; // assigns ‘b’ to ch