Primitive Data Types

Data Types and Data Structures

Primitive Type	Size	Minimum Value	Maximum Value	Wrapper Type
char	16-bit	Unicode 0	Unicode 216-1	Character
byte	8-bit	-27 (-128)	+27-1 (+127)	Byte
short	16-bit	-215 (-32,768)	+215-1 (32,767)	Short
int	32-bit	-231 (-2,147,483,648)	+231-1 (2,147,483,647)	Integer
long	64-bit	-263 (-9,223,372,036,854,775,808)	+263-1 (9,223,372,036,854,775,807)	Long
float	32-bit	32-bit IEEE 754 floating-point numbers		Float
double	64-bit	64-bit IEEE 754 floating-point numbers		Double
boolean	1-bit	true or false		Boolean
void	-----	-----	-----	Void

 

Floating-point

Floating-point numbers are like real numbers in mathematics, for example, 3.14159, -0.000001. Java has two kinds of floating-point numbers: float and double, both stored in IEEE-754 format. The default type when you write a floating-point literal is double.

Java floating-point types

type	Size		Range	Precision
name	bytes	bits	approximate	in decimal digits
float	4	32	+/- 3.4 * 1038	6-7
double	8	64	+/- 1.8 * 10308	16

Limited precision

Because there are only a limited number of bits in each floating-point type, some numbers are inexact, just as the decimal system can not represent some numbers exactly, for example 1/3. The most troublesome of these is that 1/10 can not be represented exactly in binary.

Floating-point literals

There are two types of notation for floating-point numbers. Any of these numbers can be followed by "F" (or "f") to make it a float instead of the default double.

• Standard (American) notation which is a series of digits for the integer part followed by a decimal point followed by a series of digits for the fraction part. Eg, 3.14159 is a double. A sign (+ or -) may precede the number.
• Scientific notation which is a standard floating-point literal followed by the letter "E" (or "e") followed by an optionally signed exponent of 10 which is used as a multiplier (ie, how to shift the decimal point). Generally scientific notation is used only for very large or small numbers.

Scientific	Standard
1.2345e5	123450.0
1.2345e+5	123450.0
1.2345e-5	0.000012345

Infinity and NaN

No exceptions are generated by floating-point operations. Instead of an interruption in execution, the result of an operation may be positive infinity, negative infinity, or NaN (not a number). Division by zero or overflow produce infinity. Subtracting two infinities produces a NaN. Use methods in the wrapper classes (Float or Double) to test for these values.

 부동소수 리터럴의 디폴트 데이터 타입 테스트

public class Test
{
 public static void main(String[] args)
 {
  float f = 0.123456789;

  System.out.println(f);
 }
}

Test.java:5: possible loss of precision
found   : double
required: float
                float f = 0.123456789;
                          ^
1 error
계속하려면 아무 키나 누르십시오 . . .

 float 데이터 타입의 정밀도 테스트

public class Test
{
 public static void main(String[] args)
 {
  float f = 0.123456789f;

  System.out.println(f); // 0.12345679
 }
}

0.12345679
계속하려면 아무 키나 누르십시오 . . .

 
double 형의 정밀도 테스트

public class Test
{
 public static void main(String[] args)
 {
  double d = 0.1234567890123456789d;
  // d표시는 생략가능, 부동소수표현은 디폴트로 double형

  System.out.println(d);
 }
}

0.12345678901234568
계속하려면 아무 키나 누르십시오 . . .