java.lang
Class Float

java.lang.Object
  java.lang.Float

public final class Float
extends Object

The Float class wraps a value of primitive type float in an object. An object of type Float contains a single field whose type is float.

In addition, this class provides several methods for converting a float to a String and a String to a float, as well as other constants and methods useful when dealing with a float.

Since:

JDK1.0

Field Summary

static float	MAX_VALUE A constant holding the largest positive finite value of type float, (2-2-23)·2127.
static float	MIN_VALUE A constant holding the smallest positive nonzero value of type float, 2-149.
static float	NaN A constant holding a Not-a-Number (NaN) value of type float.
static float	NEGATIVE_INFINITY A constant holding the negative infinity of type float.
static float	POSITIVE_INFINITY A constant holding the positive infinity of type float.

Constructor Summary

Float()

Method Summary

static int	floatToIntBits(float value) Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "single format" bit layout.
static float	intBitsToFloat(int bits) Returns the float value corresponding to a given bit represention.
static boolean	isInfinite(float v) Returns true if the specified number is infinitely large in magnitude, false otherwise.
static boolean	isNaN(float v) Returns true if the specified number is a Not-a-Number (NaN) value, false otherwise.
static float	parseFloat(String s) Returns a new float initialized to the value represented by the specified String, as performed by the valueOf method of class Float.
static String	toString(float f) Returns a string representation of the float argument.

Methods inherited from class java.lang.Object

clone, equals, getClass, notifyAll, toString, wait

Field Detail

POSITIVE_INFINITY

public static final float POSITIVE_INFINITY

A constant holding the positive infinity of type float. It is equal to the value returned by Float.intBitsToFloat(0x7f800000).

See Also:

Constant Field Values

NEGATIVE_INFINITY

public static final float NEGATIVE_INFINITY

A constant holding the negative infinity of type float. It is equal to the value returned by Float.intBitsToFloat(0xff800000).

See Also:

Constant Field Values

NaN

public static final float NaN

A constant holding a Not-a-Number (NaN) value of type float. It is equivalent to the value returned by Float.intBitsToFloat(0x7fc00000).

See Also:

Constant Field Values

MAX_VALUE

public static final float MAX_VALUE

A constant holding the largest positive finite value of type float, (2-2^-23)·2¹²⁷. It is equal to the value returned by Float.intBitsToFloat(0x7f7fffff).

See Also:

Constant Field Values

MIN_VALUE

public static final float MIN_VALUE

A constant holding the smallest positive nonzero value of type float, 2^-149. It is equal to the value returned by Float.intBitsToFloat(0x1).

See Also:

Constant Field Values

Constructor Detail

Float

public Float()

Method Detail

toString

public static String toString(float f)

Returns a string representation of the float argument. All characters mentioned below are ASCII characters.

• If the argument is NaN, the result is the string "NaN".
• Otherwise, the result is a string that represents the sign and magnitude (absolute value) of the argument. If the sign is negative, the first character of the result is '-' ('\u002D'); if the sign is positive, no sign character appears in the result. As for the magnitude m:
  • If m is infinity, it is represented by the characters "Infinity"; thus, positive infinity produces the result "Infinity" and negative infinity produces the result "-Infinity".
  • If m is zero, it is represented by the characters "0.0"; thus, negative zero produces the result "-0.0" and positive zero produces the result "0.0".
  • If m is greater than or equal to 10^-3 but less than 10⁷, then it is represented as the integer part of m, in decimal form with no leading zeroes, followed by '.' ('\u002E'), followed by one or more decimal digits representing the fractional part of m.
  • If m is less than 10^-3 or greater than or equal to 10⁷, then it is represented in so-called "computerized scientific notation." Let n be the unique integer such that 10ⁿ <= m < 10ⁿ⁺¹; then let a be the mathematically exact quotient of m and 10ⁿ so that 1 <= a < 10. The magnitude is then represented as the integer part of a, as a single decimal digit, followed by '.' ('\u002E'), followed by decimal digits representing the fractional part of a, followed by the letter 'E' ('\u0045'), followed by a representation of n as a decimal integer, as produced by the method Integer.toString(int).

How many digits must be printed for the fractional part of m or a? There must be at least one digit to represent the fractional part, and beyond that as many, but only as many, more digits as are needed to uniquely distinguish the argument value from adjacent values of type float. That is, suppose that x is the exact mathematical value represented by the decimal representation produced by this method for a finite nonzero argument f. Then f must be the float value nearest to x; or, if two float values are equally close to x, then f must be one of them and the least significant bit of the significand of f must be 0.

Parameters:

f - the float to be converted.

Returns:

a string representation of the argument.

parseFloat

public static float parseFloat(String s)
                        throws NumberFormatException

Returns a new float initialized to the value represented by the specified String, as performed by the valueOf method of class Float.

Parameters:

s - the string to be parsed.

Returns:

the float value represented by the string argument.

Throws:

NumberFormatException - if the string does not contain a parsable float.

Since:

1.2

See Also:

java.lang.Float#valueOf(String)

isNaN

public static boolean isNaN(float v)

Returns true if the specified number is a Not-a-Number (NaN) value, false otherwise.

Parameters:

v - the value to be tested.

Returns:

true if the argument is NaN; false otherwise.

isInfinite

public static boolean isInfinite(float v)

Returns true if the specified number is infinitely large in magnitude, false otherwise.

Parameters:

v - the value to be tested.

Returns:

true if the argument is positive infinity or negative infinity; false otherwise.

floatToIntBits

public static int floatToIntBits(float value)

Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "single format" bit layout.

Bit 31 (the bit that is selected by the mask 0x80000000) represents the sign of the floating-point number. Bits 30-23 (the bits that are selected by the mask 0x7f800000) represent the exponent. Bits 22-0 (the bits that are selected by the mask 0x007fffff) represent the significand (sometimes called the mantissa) of the floating-point number.

If the argument is positive infinity, the result is 0x7f800000.

If the argument is negative infinity, the result is 0xff800000.

If the argument is NaN, the result is 0x7fc00000.

In all cases, the result is an integer that, when given to the intBitsToFloat(int) method, will produce a floating-point value the same as the argument to floatToIntBits (except all NaN values are collapsed to a single "canonical" NaN value).

Parameters:

value - a floating-point number.

Returns:

the bits that represent the floating-point number.

intBitsToFloat

public static float intBitsToFloat(int bits)

Returns the float value corresponding to a given bit represention. The argument is considered to be a representation of a floating-point value according to the IEEE 754 floating-point "single format" bit layout.

If the argument is 0x7f800000, the result is positive infinity.

If the argument is 0xff800000, the result is negative infinity.

If the argument is any value in the range 0x7f800001 through 0x7fffffff or in the range 0xff800001 through 0xffffffff, the result is a NaN. No IEEE 754 floating-point operation provided by Java can distinguish between two NaN values of the same type with different bit patterns. Distinct values of NaN are only distinguishable by use of the Float.floatToRawIntBits method.

In all other cases, let s, e, and m be three values that can be computed from the argument:

 int s = ((bits >> 31) == 0) ? 1 : -1;
 int e = ((bits >> 23) & 0xff);
 int m = (e == 0) ?
                 (bits & 0x7fffff) << 1 :
                 (bits & 0x7fffff) | 0x800000;
 

Then the floating-point result equals the value of the mathematical expression s·m·2^e-150.

Note that this method may not be able to return a float NaN with exactly same bit pattern as the int argument. IEEE 754 distinguishes between two kinds of NaNs, quiet NaNs and signaling NaNs. The differences between the two kinds of NaN are generally not visible in Java. Arithmetic operations on signaling NaNs turn them into quiet NaNs with a different, but often similar, bit pattern. However, on some processors merely copying a signaling NaN also performs that conversion. In particular, copying a signaling NaN to return it to the calling method may perform this conversion. So intBitsToFloat may not be able to return a float with a signaling NaN bit pattern. Consequently, for some int values, floatToRawIntBits(intBitsToFloat(start)) may not equal start. Moreover, which particular bit patterns represent signaling NaNs is platform dependent; although all NaN bit patterns, quiet or signaling, must be in the NaN range identified above.

Parameters:

bits - an integer.

Returns:

the float floating-point value with the same bit pattern.