primitive : Java Glossary

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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 aka -2 gig, roughly -2 billion +2,147,483,647 [231-1] aka Integer. MAX_VALUE. aka 2 gig, roughly 2 billion 2 gig
long signed 64 8 1:19 -9,223,372,036,854,775,807 [-263] aka Long. MIN_VALUE about -9×1018 9,223,372,036,854,775,808 [+263-1] aka Long. MAX_VALUE about 9×1018 9 exabytes, or 9 billion gig
float signed exponent and mantissa 32 4 7 ±1.40129846432481707e-45 aka Float. MIN_VALUE ±3.40282346638528860e+38 aka Float. MAX_VALUE
or roughly ±2127
with about 7 significant digits of accuracy.
A float can exactly represent integers
in the range -224 to +224.		 rough, compact float
double signed exponent and mantissa 64 8 16 ±4.94065645841246544e-324 aka Double. MIN_VALUE ±1.79769313486231570e+308 aka Double. MAX_VALUE
or roughly ±21023
with 15 significant digits of accuracy, almost 16 with 15.95 significant digits.
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. double is equivalent to scientific notation, allowing very large or very small numbers with only 15 significant digits. Floating point arithmetic is not precise for a number of reasons. On the other hand, it gives you tremendous range.

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