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Introduction to Computing
Using Java
More about Primitive Types and
Operators
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
1
Default Type of Floating-point
Number Literals
 Floating-point Number literals are considered to be of
type double by default.
double
double
double
float
d1
d2
d3
f1
=
=
=
=
3.14159;
3e8;
-0.27e-5;
3.14159;
//
//
//
//
ok
ok
ok
not ok
 Adding a suffix F/ f to the number changes this default:
float
float
2008-2009 2b
f2 = 3.14159F;
f3 = -0.27e-5f;
// ok
// ok
Michael Fung, CS&E, The Chinese University of HK
2
Type Casting
 We can also apply type casting.
float f3 = (float) 3.14159;
float f4 = (float) d1;
// ok
// ok
 In case of real to integer type casts, any fractional part is
discarded, and results in the integral part (truncation):
(int) 6.3
(int) 6.8
gives 6
gives 6
 Syntax of type casting (explicit type conversion):
( <type_name> ) some_value
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
3
Type Casting Examples
double UV_measurement = 6.754;
int
UV_level
= (int) UV_measurement;
short avg_height;
avg_height = (short) ( (178.2 + 192.7 + 180.1) / 3 );
// type-casting has higher precedence than division!
Benz
peter
= new Benz();
Advanced example
Car
michael = (Car) peter;
// type-casting also works on class type objects
// peter keeps a Benz object
// we can "down-convert" it and consider it a Car
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
4
Type Casting Issues
 Integer-to-integer type casts
– byte  short  int  long
Always ok
– long  int  short  byte
May not…
– Overflow may occur, causing errors.
 Real-to-real type casts
–
–
–
–
float  double
double  float
Note that real numbers are often inexact.
Always check the accuracy you needed.
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
?
5
Issue Concerning Real Numbers
 There are infinite real numbers in the world.
 Real numbers do not have absolute friends
– There are always 第三者 in between
– 1.4  1.43  1.442  1.445  1.5
 Moreover, computers use 0 and 1 (binary digits)
to represent numbers and there is always a
limitation in representing decimal real numbers.
 You will find that 0.7 * 0.7  0.49 and
(double) 3.123F gives 3.122999906539917
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
6
Self-study: More About Type
class DataType {
/* testing of primitive data types */
public static void main (String [ ] args) {
byte int8 = -128;
System.out.println(int8);
int8 = (byte) 137;
/* type casting with an overflow */
System.out.println(int8);
boolean ok = (3 > 7); /* boolean expression */
System.out.println(ok);
System.out.println("Hello \"World\" !!!");
double GPA = 3;
System.out.println("GPA = " + GPA);
System.out.println("(int)(5.23)
= " + (int)(5.23));
System.out.println("Math.floor(5.23) = " + Math.floor(5.23));
System.out.println("Math.ceil(5.23) = " + Math.ceil(5.23));
System.out.println("Math.round(5.23) = " + Math.round(5.23));
System.out.println("(int)(-5.23)
= " + (int)(-5.23));
System.out.println("Math.floor(-5.23) = " + Math.floor(-5.23));
System.out.println("Math.ceil(-5.23) = " + Math.ceil(-5.23));
System.out.println("Math.round(-5.23) = " + Math.round(-5.23));
}
}
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
7
Self-study: More About Type
-128
Look up Java API class Math
-119
check these Math methods:
false
floor( )
Hello "World" !!!
round( )
GPA = 3.0
(int)(5.23)
= 5
ceil( )
Math.floor(5.23) = 5.0 What are their functions?
Math.ceil(5.23) = 6.0
Do they act like a
Math.round(5.23) = 5
mathematical function?
(int)(-5.23)
= -5
Math.floor(-5.23) = -6.0
Math.ceil(-5.23) = -5.0
Math.round(-5.23) = -5
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
8
The Math Class
 The class Math is provided with Java, offering
various methods for simple mathematical
operations.
 To use such methods, we have to send message to
the Math class:
double answer1;
answer1 = Math.sqrt(49);
 A message usually generates a result (depending
on the design and nature/type of the method):
long
answer2;
answer2 = Math.round(Math.pow(2+3, 2));
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
9
Methods in the Math Class
 PI is a class constant field pre-
stored with many digits of .
 Notice that sin, cos, tan, etc.
uses radian instead of degree.
Math
PI
3.14159…
sqrt
 Don’t miss the pair of parenthesis in
pow
sending messages to the Math class!
sin
 General form of a such a message:
class_name.method_name(input);
Math.function(input);
2008-2009 2b
round
…
Michael Fung, CS&E, The Chinese University of HK
10
Operators
Category of operators:
– Arithmetic
– Relational
– Logical
: +
: <
: !
–
>
&
* / % -num
<= >= == !=
| && || ^
– Conditional :
bool_expression ? true_case : false_case
– Short-hand : ++ -- += -=
– Assignment : = (to store a value)
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
*= …
11
Arithmetic Operators
Addition/ Sum
:a+b
Subtraction/ Difference
:a–b
Multiplication/ Product
:a*b
Division/ Quotient
:a/b
Remainder (of integer division): a % b
Negation/ Minus
: –number
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
12
Real and Integer Division
 System.out.println(1.0 / 2.0);
 0.5
 System.out.println(1 / 2);
 0
 System.out.println(1.0 / 2);
 0.5
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
13
Real and Integer Division
 System.out.println(1.0 / 2.0);
 0.5
double / double
 System.out.println(1 / 2);
 0
 System.out.println(1.0 / 2);
 0.5
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
14
Real and Integer Division
 System.out.println(1.0 / 2.0);
 0.5
double / double
 System.out.println(1 / 2);
 0
int / int  int
 System.out.println(1.0 / 2);
 0.5
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
15
Real and Integer Division
 System.out.println(1.0 / 2.0);
 0.5
double / double
 System.out.println(1 / 2);
 0
int / int  int
 System.out.println(1.0 / 2);
 0.5
2008-2009 2b
double / int
Michael Fung, CS&E, The Chinese University of HK
16
Real and Integer Division
 System.out.println(1.0 / 2.0);
 0.5
double / double
 System.out.println(1 / 2);
 0
int / int  int
 System.out.println(1.0 / 2);
 0.5
2008-2009 2b
double / double
Implicit Coercion
Michael Fung, CS&E, The Chinese University of HK
17
Relational and Logical Operators
(Examples will be covered in tutorial)
Relational operators
– to make comparisons
– result is a boolean value (true or false)
Logical/ Boolean operators
– and, or, negate, exclusive-or, …
– operate on boolean values
– result is a boolean value
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
18
Short-hand Operators
 Increment operator (basic understanding)
a++  ++a  a = a + 1
 Decrement operator (basic understanding)
a––  --a  a = a – 1
 Short-hand assignment operators (lazy)
a += b  a = a + b
a -= b  a = a – b
a *= b  a = a * b
...
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
19
Summary
 Type casting usage and examples
 Floating-point number issues
 Java API Math class and methods
 Operators usage and examples
– Conditional operator will be discussed later
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
20
End Note
 Readings and References
– Section 2.1 – 2.5
 Exercise
– 1.3, 1.4, 1.16, 1.17, 1.18,
– 2.2, 2.3, 2.4, 2.5, 2.6, 2.7
 Programming Projects
– 2.1
2008-2009 2b
Michael Fung, CS&E, The Chinese University of HK
21