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' [2^{16}1] aka Character. MAX_VALUE  Unicode chars are twice as big as C’s. 
byte  signed  8  1  2:3  128 [2^{7}] aka Byte. MIN_VALUE  +127 [2^{7}1]aka Byte. MAX_VALUE  Bytes are signed, so half the usual 255 range. 
short  signed  16  2  4:5  32,768 [2^{15}] aka Short. MIN_VALUE  +32,767 [2^{15}1] aka Short. MAX_VALUE  32K 
int  signed  32  4  9:10  2,147,483,648 [2^{31}] aka Integer.MIN_VALUE aka 2 gig, roughly 2 billion  +2,147,483,647 [2^{31}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 [2^{63}] aka Long. MIN_VALUE about 9×10^{18}  9,223,372,036,854,775,808 [+2^{63}1] aka Long. MAX_VALUE about 9×10^{18}  9 exabytes, or 9 billion gig 
float  signed exponent and mantissa  32  4  7  ±1.40129846432481707e45 aka Float. MIN_VALUE  ±3.40282346638528860e+38 aka Float.
MAX_VALUE
or roughly ±2^{127} with about 7 significant digits of accuracy. A float can exactly represent integers in the range 2^{24} to +2^{24}. 
rough, compact float 
double  signed exponent and mantissa  64  8  16  ±4.94065645841246544e324 aka Double. MIN_VALUE  ±1.79769313486231570e+308 aka Double.
MAX_VALUE
or roughly ±2^{1023} with 15 significant digits of accuracy, almost 16 with 15.95 significant digits. A double can exactly represent integers in the range 2^{53} to +2^{53}. 
high precision float 
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 32bit quantities.
For small 8bit quantities you can use byte either signed or unsigned. For 16bit unsigned, use char, and 16bit 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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