The Java Lesson 3: Identifiers and primitive data types. Page 2
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Primitive data
types
1. Uses of identifiers in Java  2. Primitive data types in Java

Are part of the language
(builtin)

Represent different kinds and
sizes of data

Are always the same regardless
of the platform
Type 
Bit Size 
Usage 
Signed 
Range of Values 
boolean 
1 
true or false 
no 
true or false 
char 
16 
Unicode character 
no 
0 to 2^{16}  1 
byte 
8 
very small integer number 
yes 
2^{7} to 2^{7}  1 
short 
16 
small integer number 
yes 
2^{15} to 2^{15}  1 
int 
32 
integer number 
yes 
2^{31} to 2^{31}  1 
long 
64 
large integer number 
yes 
2^{63} to 2^{63}  1 
float 
32 
single precision decimal number 
yes 
+ 3.4e^{38} to +
1.4e^{45} 
double 
64 
double precision decimal number 
yes 
+ 1.8e^{308} to +
4.9e^{324} 
What about strings?
What is Unicode?

An international (ISO)
standard. For detailed information, go to http://www.unicode.org/

Provides a unique bit
pattern to represent every character or symbol in all the world's character
sets

Each character has an
equivalent, positive integer value corresponding to the bit pattern
Integer data format
Uses two'scomplement
notation. To determine the bit pattern of an integer value:

If the number is greater than
or equal to zero: convert it to binary

If the number is
negative: take its absolute value, subtract one, convert the result to
binary, and reverse all the bits
The leftmost (highorder) bit
is the sign bit with 0 indicating positive and 1 indicating
negative.
Here are some examples using a
16 bit (short) data
format:
Action 
Base 10 
Binary 
Hexadecimal 
Integer to be
represented 
5 


1. Absolute value 
5 


2. Minus 1 
4 
0000 0000 0000 0100 
0004 
3. Reverse bits 

1111 1111 1111 1011 
FFFB 

Integer to be
represented 
67 
0000 0000 0100 0011 
0043 

Integer to be
represented 
44 


1. Absolute value 
44 


2. Minus 1 
43 
0000 0000 0010 1011 
002B 
3. Reverse bits 

1111 1111 1101 0100 
FFD4 
For simplicity, hexadecimal
(base 16) notation is used to represent binary numbers. Each hexadecimal digit
represents four binary digits as follows:
Hexadecimal Digit 
Binary
Equivalent 
0 
0000 
1 
0001 
2 
0010 
3 
0011 
4 
0100 
5 
0101 
6 
0110 
7 
0111 
8 
1000 
9 
1001 
A 
1010 
B 
1011 
C 
1100 
D 
1101 
E 
1110 
F 
1111 
Floatingpoint (decimal)
types

Conform to the IEEE 754
specification for representing real numbers in a binary format. For the
certification exam, you will not need to know the internal representation or
the range of maximum and minimum values.

double allows up for twice as many significant
digits as float and
should be used when extremely large numbers or greater precision are required
More information
Java ranch has two great
tutorials relating to topics covered in this lesson. Be sure to read the
following "campfire stories":
Review questions

Which of the following are
valid Java identifiers? (choose three)

_$amount_due_2002

2002_sales

class

String

FINANCE_CHARGE

Which primitive data type
may be used to store the integer value 473 ? (choose three)

char

byte

short

int

long

Which of the following
hexadecimal values might represent the contents of a negative, int variable? (choose two)

1AF21110

C8253B7C

F63A

FFFFFFFFFFFFFFFF

90001C58

In hexadecimal notation,
what is the value of 100 as a byte?

FF9C

9C

FF9B

9B

a byte is too small an area to hold the value
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