1、常量定义：SIZE=32；BYTES=4
/**
* A constant holding the positive infinity of type
* {@code float}. It is equal to the value returned by
* {@code Float.intBitsToFloat(0x7f800000)}.
*/
public static final float POSITIVE_INFINITY = 1.0f / 0.0f;
/**
* A constant holding the negative infinity of type
* {@code float}. It is equal to the value returned by
* {@code Float.intBitsToFloat(0xff800000)}.
*/
public static final float NEGATIVE_INFINITY = -1.0f / 0.0f;
/**
* A constant holding a Not-a-Number (NaN) value of type
* {@code float}. It is equivalent to the value returned by
* {@code Float.intBitsToFloat(0x7fc00000)}.
*/
public static final float NaN = 0.0f / 0.0f;
/**
* A constant holding the largest positive finite value of type
* {@code float}, (2-2<sup>-23</sup>)·2<sup>127</sup>.
* It is equal to the hexadecimal floating-point literal
* {@code 0x1.fffffeP+127f} and also equal to
* {@code Float.intBitsToFloat(0x7f7fffff)}.
*/
public static final float MAX_VALUE = 0x1.fffffeP+127f; // 3.4028235e+38f
/**
* A constant holding the smallest positive normal value of type
* {@code float}, 2<sup>-126</sup>. It is equal to the
* hexadecimal floating-point literal {@code 0x1.0p-126f} and also
* equal to {@code Float.intBitsToFloat(0x00800000)}.
*
* @since 1.6
*/
public static final float MIN_NORMAL = 0x1.0p-126f; // 1.17549435E-38f
/**
* A constant holding the smallest positive nonzero value of type
* {@code float}, 2<sup>-149</sup>. It is equal to the
* hexadecimal floating-point literal {@code 0x0.000002P-126f}
* and also equal to {@code Float.intBitsToFloat(0x1)}.
*/
public static final float MIN_VALUE = 0x0.000002P-126f; // 1.4e-45f
/**
* Maximum exponent a finite {@code float} variable may have. It
* is equal to the value returned by {@code
* Math.getExponent(Float.MAX_VALUE)}.
*
* @since 1.6
*/
public static final int MAX_EXPONENT = 127;
/**
* Minimum exponent a normalized {@code float} variable may have.
* It is equal to the value returned by {@code
* Math.getExponent(Float.MIN_NORMAL)}.
*
* @since 1.6
*/
public static final int MIN_EXPONENT = -126;
/**
* The number of bits used to represent a {@code float} value.
*
* @since 1.5
*/
public static final int SIZE = 32;
/**
* The number of bytes used to represent a {@code float} value.
*
* @since 1.8
*/
public static final int BYTES = SIZE / Byte.SIZE;2、hashCode与equals
hashCode直接返回float的位信息，equls根据位信息进行比较。与Double的区别是Double64位使用long型，float是32位使用int型
public static int hashCode(float value) {
return floatToIntBits(value);
}
/**
* Compares this object against the specified object. The result
* is {@code true} if and only if the argument is not
* {@code null} and is a {@code Float} object that
* represents a {@code float} with the same value as the
* {@code float} represented by this object. For this
* purpose, two {@code float} values are considered to be the
* same if and only if the method {@link #floatToIntBits(float)}
* returns the identical {@code int} value when applied to
* each.
*
* <p>Note that in most cases, for two instances of class
* {@code Float}, {@code f1} and {@code f2}, the value
* of {@code f1.equals(f2)} is {@code true} if and only if
*
* <blockquote><pre>
* f1.floatValue() == f2.floatValue()
* </pre></blockquote>
*
* <p>also has the value {@code true}. However, there are two exceptions:
* <ul>
* <li>If {@code f1} and {@code f2} both represent
* {@code Float.NaN}, then the {@code equals} method returns
* {@code true}, even though {@code Float.NaN==Float.NaN}
* has the value {@code false}.
* <li>If {@code f1} represents {@code +0.0f} while
* {@code f2} represents {@code -0.0f}, or vice
* versa, the {@code equal} test has the value
* {@code false}, even though {@code 0.0f==-0.0f}
* has the value {@code true}.
* </ul>
*
* This definition allows hash tables to operate properly.
*
* @param obj the object to be compared
* @return {@code true} if the objects are the same;
* {@code false} otherwise.
* @see java.lang.Float#floatToIntBits(float)
*/
public boolean equals(Object obj) {
return (obj instanceof Float)
&& (floatToIntBits(((Float)obj).value) == floatToIntBits(value));
}
/**
* Returns a representation of the specified floating-point value
* according to the IEEE 754 floating-point "single format" bit
* layout.
*
* <p>Bit 31 (the bit that is selected by the mask
* {@code 0x80000000}) represents the sign of the floating-point
* number.
* Bits 30-23 (the bits that are selected by the mask
* {@code 0x7f800000}) represent the exponent.
* Bits 22-0 (the bits that are selected by the mask
* {@code 0x007fffff}) represent the significand (sometimes called
* the mantissa) of the floating-point number.
*
* <p>If the argument is positive infinity, the result is
* {@code 0x7f800000}.
*
* <p>If the argument is negative infinity, the result is
* {@code 0xff800000}.
*
* <p>If the argument is NaN, the result is {@code 0x7fc00000}.
*
* <p>In all cases, the result is an integer that, when given to the
* {@link #intBitsToFloat(int)} method, will produce a floating-point
* value the same as the argument to {@code floatToIntBits}
* (except all NaN values are collapsed to a single
* "canonical" NaN value).
*
* @param value a floating-point number.
* @return the bits that represent the floating-point number.
*/
public static int floatToIntBits(float value) {
int result = floatToRawIntBits(value);
// Check for NaN based on values of bit fields, maximum
// exponent and nonzero significand.
if ( ((result & FloatConsts.EXP_BIT_MASK) ==
FloatConsts.EXP_BIT_MASK) &&
(result & FloatConsts.SIGNIF_BIT_MASK) != 0)
result = 0x7fc00000;
return result;
}3、最大值
a与b都为0.0时，a为-0则返回b
public static float max(float a, float b) {
if (a != a)
return a; // a is NaN
if ((a == 0.0f) &&
(b == 0.0f) &&
(Float.floatToRawIntBits(a) == negativeZeroFloatBits)) {
// Raw conversion ok since NaN can't map to -0.0.
return b;
}
return (a >= b) ? a : b;
}4、最小值
a与b都为0.0时，b为-0则返回b
public static float min(float a, float b) {
if (a != a)
return a; // a is NaN
if ((a == 0.0f) &&
(b == 0.0f) &&
(Float.floatToRawIntBits(b) == negativeZeroFloatBits)) {
// Raw conversion ok since NaN can't map to -0.0.
return b;
}
return (a <= b) ? a : b;
}
