Share via

20.9 The Class java.lang.Float

  • Article
public final class Float extends Number {
 public static final float MIN_VALUE = 1.4e-45f;
 public static final float MAX_VALUE = 3.4028235e+38f;
 public static final float NEGATIVE_INFINITY = -1.0f/0.0f;
 public static final float POSITIVE_INFINITY = 1.0f/0.0f;
 public static final float NaN = 0.0f/0.0f;
 public Float(float value);
 public Float(double value);
 public Float(String s)
        throws NumberFormatException;
 public String toString();
 public boolean equals(Object obj);
 public int hashCode();
 public int intValue();
 public long longValue();
 public float floatValue();
 public double doubleValue();
 public static String toString(float f);
 public static Float valueOf(String s)
        throws NullPointerException, NumberFormatException;
 public boolean isNaN();
 public static boolean isNaN(float v);
 public boolean isInfinite();
 public static boolean isInfinite(float v);
 public static int floatToIntBits(float value);
 public static float intBitsToFloat(int bits);
}

20.9.1 public static final float MIN_VALUE = 1.4e-45f;

The constant value of this field is the smallest positive nonzero value of type float. It is equal to the value returned by Float.intBitsToFloat(0x1).

20.9.2 public static final float MAX_VALUE = 3.4028235e+38f;

The constant value of this field is the largest positive finite value of type float. It is equal to the value returned by Float.intBitsToFloat(0x7f7fffff).

20.9.3 public static final float NEGATIVE_INFINITY =-1.0f/0.0f;

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

20.9.4 public static final float POSITIVE_INFINITY =1.0f/0.0f;

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

20.9.5 public static final float NaN = 0.0f/0.0f;

The constant value of this field is the Not-a-Number value of type float. It is equal to the value returned by Float.intBitsToFloat(0x7fc00000).

20.9.6 public Float(float value)

This constructor initializes a newly created Float object so that it represents the primitive value that is the argument.

20.9.7 public Float(double value)

This constructor initializes a newly created Float object so that it represents the result of narrowing (§5.1.3) the argument from type double to type float.

20.9.8 public Float(String s) throws NumberFormatException

This constructor initializes a newly created Float object so that it represents the floating-point value of type float represented by the string. The string is converted to a float value in exactly the manner used by the valueOf method (§20.9.17).

20.9.9 public String toString()

The primitive float value represented by this Float object is converted to a string exactly as if by the method toString of one argument (§20.9.16).

Overrides the toString method of Object(§20.1.2).

20.9.10 public boolean equals(Object obj)

The result is true if and only if the argument is not null and is a Float object that represents the same float value as this Float object. For this purpose, two float values are considered to be the same if and only if the method floatToIntBits(§20.9.22) returns the same int value when applied to each. Note that even though the == operator returns false if both operands are NaN, this equals method will return true if this Float object and the argument are both Float objects that represent NaN. On the other hand, even though the == operator returns true if one operand is positive zero and the other is negative zero, this equals method will return false if this Float object and the argument represent zeroes of different sign. This definition allows hashtables to operate properly.

Overrides the equals method of Object(§20.1.3).

20.9.11 public int hashCode()

The result is the integer bit representation, exactly as produced by the method floatToIntBits(§20.9.22), of the primitive float value represented by this Float object.

Overrides the hashCode method of Object(§20.1.4).

20.9.12 public int intValue()

The float value represented by this Float object is converted (§5.1.3) to type int and the result of the conversion is returned.

Overrides the intValue method of Number(§20.6.1).

20.9.13 public long longValue()

The float value represented by this Float object is converted (§5.1.3) to type long and the result of the conversion is returned.

Overrides the longValue method of Number(§20.6.2).

20.9.14 public float floatValue()

The float value represented by this Float object is returned.

Overrides the floatValue method of Number(§20.6.3).

20.9.15 public double doubleValue()

The float value represented by this Float object is converted (§5.1.2) to type double and the result of the conversion is returned.

Overrides the doubleValue method of Number(§20.6.4).

20.9.16 public static String toString(float f)

The argument is converted to a readable string format as follows. All characters and characters in strings 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 but less than , 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 or not less than , then it is represented in so-called "computerized scientific notation." Let n be the unique integer such that ; then let a be the mathematically exact quotient of m and so that . 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 of one argument (§20.7.12).

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.

[This specification for the method toString is scheduled for introduction in Java version 1.1. In previous versions of Java, this method produces Inf instead of Infinity for infinite values. Also, it renders finite values in the same form as the %g format of the printf function in the C programming language, which can lose precision because it produces at most six digits after the decimal point.]

20.9.17 public static Float valueOf(String s)throws NullPointerException, NumberFormatException

The string s is interpreted as the representation of a floating-point value and a Float object representing that value is created and returned.

If s is null, then a NullPointerException is thrown.

Leading and trailing whitespace (§20.5.19) characters in s are ignored. The rest of s should constitute a FloatValue as described by the lexical syntax rules:

FloatValue:
SignoptDigits . DigitsoptExponentPartopt

    Signopt. DigitsExponentPartopt

where Sign, Digits, and ExponentPart are as defined in §3.10.2. If it does not have the form of a FloatValue, then a NumberFormatException is thrown. Otherwise, it 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. Finally, a new object of class Float is created to represent this float value.

Note that neither F nor f is permitted to appear in s as a type indicator, as would be permitted in Java source code (§3.10.1).

20.9.18 public boolean isNaN()

The result is true if and only if the value represented by this Float object is NaN.

20.9.19 public static boolean isNaN(float v)

The result is true if and only if the value of the argument is NaN.

20.9.20 public boolean isInfinite()

The result is true if and only if the value represented by this Float object is positive infinity or negative infinity.

20.9.21 public static boolean isInfinite(float v)

The result is true if and only if the value of the argument is positive infinity or negative infinity.

20.9.22 public static int floatToIntBits(float value)

The result is a representation of the floating-point argument 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 will be 0x7f800000.
  • If the argument is negative infinity, the result will be 0xff800000.
  • If the argument is NaN, the result will be 0x7fc00000.

In all cases, the result is an integer that, when given to the intBitsToFloat method (§20.9.23), will produce a floating-point value equal to the argument to floatToIntBits.

20.9.23 public static float intBitsToFloat(int bits)

The argument is considered to be a representation of a floating-point value according to the IEEE 754 floating-point "single format" bit layout. That floating-point value is returned as the result.

  • If the argument is 0x7f800000, the result will be positive infinity.
  • If the argument is 0xff800000, the result will be negative infinity.
  • If the argument is any value in the range 0x7f800001 through 0x7fffffff or in the range 0xff800001 through 0xffffffff, the result will be NaN. (All IEEE 754 NaN values are, in effect, lumped together by the Java language into a single value called NaN.)
  • 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 .