primitive : Java Glossary

2007-09-25 by Roedy Green ©1996-2009 Canadian Mind Products
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primitive

Primitive variables include boolean, char, byte, short, int, long, float and double. Strings, arrays and Objects are not considered primitives.

Java Primitives
Type	Signed?	Bits	Bytes	Digits	Lowest	Highest	Mnemonic
boolean	n/a	1	1	1	false	true	zero/one
char	unsigned Unicode	16	2	4:5	'\u0000' [0] aka Character.MIN_VALUE	'\uffff' [2¹⁶-1] aka Character. MAX_VALUE	Unicode chars are twice as big as C’s.
byte	signed	8	1	2:3	-128 [-2⁷] aka Byte. MIN_VALUE	+127 [2⁷-1]aka Byte. MAX_VALUE	Bytes are signed, so half the usual 255 range.
short	signed	16	2	4:5	-32,768 [-2¹⁵] aka Short. MIN_VALUE	+32,767 [2¹⁵-1] aka Short. MAX_VALUE	32K
int	signed	32	4	9:10	-2,147,483,648 [-2³¹] aka Integer. MIN_VALUE	+2,147,483,647 [2³¹-1] aka Integer. MAX_VALUE	2 gig
long	signed	64		:	[-2⁶³] aka Long. MIN_VALUE	[2⁶³-1] aka Long. MAX_VALUE	exabytes, or billion gig
float	signed exponent and mantissa			:	±1.40129846432481707e-45 aka Float.MIN_VALUE	±3.40282346638528860e+38 aka Float.MAX_VALUE or roughly ±2¹²⁷ with to significant digits of accuracy. A float can exactly represent integers in the range -2²⁴ to +2²⁴.	rough, compact float
double	signed exponent and mantissa			:	±4.94065645841246544e-324 aka Double.MIN_VALUE	±1.79769313486231570e+308 aka Double.MAX_VALUE or roughly ±2¹⁰²³ with to significant digits of accuracy. A double can exactly represent integers in the range -2⁵³ to +2⁵³.	high precision float

When do you use float and when double? It depends how much precision you need. Because modern floating point hardware is all built on double, normally the only time you use float is for float[] or for float fields in plentiful Objects to conserve space when you don’t need the precision.

Similarly you normally use int in preference to short, char or byte except in arrays or Object fields, even when you don’t need the extra range because modern computer hardware is based around 32-bit quantities.

When To Use Various Types

If you want a precise value, or you are counting things, use int or long depending on how big the value is or how big the result of a calculation can be. If the value is too fat to fit in a long use BigInteger or BigDecimal.

For small 8-bit quantities you can use byte either signed or unsigned. For 16-bit unsigned, use char, and 16-bit signed use short. Normally you use int, except for arrays or objects, since ints are generally faster, though they take more room.

If the value is a measurement of a physical quantity, use a double or float depending on the accuracy required. It equivalent to scientific notation, allowing very large or very small numbers with only about 15 significant digits. Floating point arithmetic is not precise for a number of reasons. On the other hand, it gives you tremendous range.

binary formats
corner case
currency
floating point
IEEE 754 Floating point format
int vs Integer: float vs Float etc
Java Cheat Sheet
literal
sizeof
unsigned

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