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Float (Java 2 Platform SE v1.4.1) - JDK 5 Documentation v1.4.1, Java 2 SDK 英文文档

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JavaTM 2 Platform
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java.lang
Class Float

java.lang.Object
  |
  +--java.lang.Number
        |
        +--java.lang.Float
All Implemented Interfaces:
Comparable, Serializable
public final class Float
extends Number
implements Comparable

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
See Also:
Serialized Form

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.
static Class TYPE
          The Class instance representing the primitive type float.
 
Constructor Summary
Float(double value)
          Constructs a newly allocated Float object that represents the argument converted to type float.
Float(float value)
          Constructs a newly allocated Float object that represents the primitive float argument.
Float(String s)
          Constructs a newly allocated Float object that represents the floating-point value of type float represented by the string.
 
Method Summary
 byte byteValue()
          Returns the value of this Float as a byte (by casting to a byte).
static int compare(float f1, float f2)
          Compares the two specified float values.
 int compareTo(Float anotherFloat)
          Compares two Float objects numerically.
 int compareTo(Object o)
          Compares this Float object to another object.
 double doubleValue()
          Returns the double value of this Float object.
 boolean equals(Object obj)
          Compares this object against the specified object.
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 int floatToRawIntBits(float value)
          Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "single format" bit layout, preserving Not-a-Number (NaN) values.
 float floatValue()
          Returns the float value of this Float object.
 int hashCode()
          Returns a hash code for this Float object.
static float intBitsToFloat(int bits)
          Returns the float value corresponding to a given bit represention.
 int intValue()
          Returns the value of this Float as an int (by casting to type int).
 boolean isInfinite()
          Returns true if this Float value is infinitely large in magnitude, false otherwise.
static boolean isInfinite(float v)
          Returns true if the specified number is infinitely large in magnitude, false otherwise.
 boolean isNaN()
          Returns true if this Float value is a Not-a-Number (NaN), false otherwise.
static boolean isNaN(float v)
          Returns true if the specified number is a Not-a-Number (NaN) value, false otherwise.
 long longValue()
          Returns value of this Float as a long (by casting to type long).
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.
 short shortValue()
          Returns the value of this Float as a short (by casting to a short).
 String toString()
          Returns a string representation of this Float object.
static String toString(float f)
          Returns a string representation of the float argument.
static Float valueOf(String s)
          Returns a Float object holding the float value represented by the argument string s.
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, 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

TYPE

public static final Class TYPE
The Class instance representing the primitive type float.

Since:
JDK1.1
Constructor Detail

Float

public Float(float value)
Constructs a newly allocated Float object that represents the primitive float argument.

Parameters:
value - the value to be represented by the Float.

Float

public Float(double value)
Constructs a newly allocated Float object that represents the argument converted to type float.

Parameters:
value - the value to be represented by the Float.

Float

public Float(String s)
      throws NumberFormatException
Constructs a newly allocated Float object that represents the floating-point value of type float represented by the string. The string is converted to a float value as if by the valueOf method.

Parameters:
s - a string to be converted to a Float.
Throws:
NumberFormatException - if the string does not contain a parsable number.
See Also:
valueOf(java.lang.String)
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.

To create localized string representations of a floating-point value, use subclasses of NumberFormat.

Parameters:
f - the float to be converted.
Returns:
a string representation of the argument.

valueOf

public static Float valueOf(String s)
                     throws NumberFormatException
Returns a Float object holding the float value represented by the argument string s.

If s is null, then a NullPointerException is thrown.

Leading and trailing whitespace characters in s are ignored. The rest of s should constitute a FloatValue as described by the lexical syntax rules:

FloatValue:
Signopt NaN
Signopt Infinity
Signopt FloatingPointLiteral
where Sign and FloatingPointLiteral are as defined in §3.10.2 of the Java Language Specification. If s does not have the form of a FloatValue, then a NumberFormatException is thrown. Otherwise, s is regarded as representing an exact decimal value in the usual "computerized scientific notation"; this exact decimal value is then conceptually converted to an "infinitely precise" binary value that is then rounded to type float by the usual round-to-nearest rule of IEEE 754 floating-point arithmetic, which includes preserving the sign of a zero value. Finally, a Float object representing this float value is returned.

To interpret localized string representations of a floating-point value, use subclasses of NumberFormat.

Parameters:
s - the string to be parsed.
Returns:
a Float object holding the value represented by the String argument.
Throws:
NumberFormatException - if the string does not contain a parsable number.

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:
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.

isNaN

public boolean isNaN()
Returns true if this Float value is a Not-a-Number (NaN), false otherwise.

Returns:
true if the value represented by this object is NaN; false otherwise.

isInfinite

public boolean isInfinite()
Returns true if this Float value is infinitely large in magnitude, false otherwise.

Returns:
true if the value represented by this object is positive infinity or negative infinity; false otherwise.

toString

public String toString()
Returns a string representation of this Float object. The primitive float value represented by this object is converted to a String exactly as if by the method toString of one argument.

Overrides:
toString in class Object
Returns:
a String representation of this object.
See Also:
toString(float)

byteValue

public byte byteValue()
Returns the value of this Float as a byte (by casting to a byte).

Overrides:
byteValue in class Number
Returns:
the float value represented by this object converted to type byte

shortValue

public short shortValue()
Returns the value of this Float as a short (by casting to a short).

Overrides:
shortValue in class Number
Returns:
the float value represented by this object converted to type short
Since:
JDK1.1

intValue

public int intValue()
Returns the value of this Float as an int (by casting to type int).

Specified by:
intValue in class Number
Returns:
the float value represented by this object converted to type int

longValue

public long longValue()
Returns value of this Float as a long (by casting to type long).

Specified by:
longValue in class Number
Returns:
the float value represented by this object converted to type long

floatValue

public float floatValue()
Returns the float value of this Float object.

Specified by:
floatValue in class Number
Returns:
the float value represented by this object

doubleValue

public double doubleValue()
Returns the double value of this Float object.

Specified by:
doubleValue in class Number
Returns:
the float value represented by this object is converted to type double and the result of the conversion is returned.

hashCode

public int hashCode()
Returns a hash code for this Float object. The result is the integer bit representation, exactly as produced by the method floatToIntBits(float), of the primitive float value represented by this Float object.

Overrides:
hashCode in class Object
Returns:
a hash code value for this object.
See Also:
Object.equals(java.lang.Object), Hashtable

equals

public boolean equals(Object obj)
Compares this object against the specified object. The result is true if and only if the argument is not null and is a Float object that represents a float with the same value as the float represented by this object. For this purpose, two float values are considered to be the same if and only if the method floatToIntBits(float) returns the identical int value when applied to each.

Note that in most cases, for two instances of class Float, f1 and f2, the value of f1.equals(f2) is true if and only if 

   f1.floatValue() == f2.floatValue()

also has the value true. However, there are two exceptions:

  • If f1 and f2 both represent Float.NaN, then the equals method returns true, even though Float.NaN==Float.NaN has the value false.
  • If f1 represents +0.0f while f2 represents -0.0f, or vice versa, the equal test has the value false, even though 0.0f==-0.0f has the value true.
This definition allows hash tables to operate properly.

Overrides:
equals in class Object
Parameters:
obj - the object to be compared
Returns:
true if the objects are the same; false otherwise.
See Also:
floatToIntBits(float)

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.

floatToRawIntBits

public static int floatToRawIntBits(float value)
Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "single format" bit layout, preserving Not-a-Number (NaN) values.

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 the integer representing the actual NaN value. Unlike the floatToIntBits method, intToRawIntBits does not collapse all the bit patterns encoding a NaN to a single "canonical" NaN value.

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 floatToRawIntBits.

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·2e-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.

compareTo

public int compareTo(Float anotherFloat)
Compares two Float objects numerically. There are two ways in which comparisons performed by this method differ from those performed by the Java language numerical comparison operators (<, <=, ==, >= >) when applied to primitive float values:
  • Float.NaN is considered by this method to be equal to itself and greater than all other float values (including Float.POSITIVE_INFINITY).
  • 0.0f is considered by this method to be greater than -0.0f.
This ensures that Float.compareTo(Object) (which forwards its behavior to this method) obeys the general contract for Comparable.compareTo, and that the natural order on Floats is consistent with equals.

Parameters:
anotherFloat - the Float to be compared.
Returns:
the value 0 if anotherFloat is numerically equal to this Float; a value less than 0 if this Float is numerically less than anotherFloat; and a value greater than 0 if this Float is numerically greater than anotherFloat.
Since:
1.2
See Also:
Comparable.compareTo(Object)

compareTo

public int compareTo(Object o)
Compares this Float object to another object. If the object is a Float, this function behaves like compareTo(Float). Otherwise, it throws a ClassCastException (as Float objects are comparable only to other Float objects).

Specified by:
compareTo in interface Comparable
Parameters:
o - the Object to be compared.
Returns:
the value 0 if the argument is a Float numerically equal to this Float; a value less than 0 if the argument is a Float numerically greater than this Float; and a value greater than 0 if the argument is a Float numerically less than this Float .
Throws:
ClassCastException - if the argument is not a Float.
Since:
1.2
See Also:
Comparable

compare

public static int compare(float f1,
                          float f2)
Compares the two specified float values. The sign of the integer value returned is the same as that of the integer that would be returned by the call: 
    new Float(f1).compareTo(new Float(f2))

Parameters:
f1 - the first float to compare.
f2 - the second float to compare.
Returns:
the value 0 if f1 is numerically equal to f2; a value less than 0 if f1 is numerically less than f2; and a value greater than 0 if f1 is numerically greater than f2.
Since:
1.4
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JavaTM 2 Platform
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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.