Float.java

/*
 * Copyright (c) 1994, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang;

import jdk.internal.HotSpotIntrinsicCandidate;
import jdk.internal.math.FloatingDecimal;

/**
 * The {@code Float} class wraps a value of primitive type
 * {@code float} in an object. An object of type
 * {@code Float} contains a single field whose type is
 * {@code float}.
 *
 * <p>In addition, this class provides several methods for converting a
 * {@code float} to a {@code String} and a
 * {@code String} to a {@code float}, as well as other
 * constants and methods useful when dealing with a
 * {@code float}.
 *
 * @author Lee Boynton
 * @author Arthur van Hoff
 * @author Joseph D. Darcy
 * @since 1.0
 */
// float的包装类
public final class Float extends Number implements Comparable<Float> {
    
    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = -2671257302660747028L;
    
    /**
     * The {@code Class} instance representing the primitive type
     * {@code float}.
     *
     * @since 1.1
     */
    // 相当于float.class
    @SuppressWarnings("unchecked")
    public static final Class<Float> TYPE = (Class<Float>) Class.getPrimitiveClass("float");
    
    /**
     * 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;  // 代表正无穷大
    
    /**
     * 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; // 代表负无穷大
    
    /**
     * 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; // 代表非数字
    
    /**
     * A constant holding the largest positive finite value of type
     * {@code float}, (2-2<sup>-23</sup>)&middot;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; // float最大值：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; // float最小正值：1.17549435E-38f，正规数
    
    /**
     * 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; // float最小正值：1.4e-45f，次正规数
    
    /**
     * 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; // float二进制形式指数部分最大值
    
    /**
     * 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; // float二进制形式指数部分最小值
    
    /**
     * The number of bits used to represent a {@code float} value.
     *
     * @since 1.5
     */
    public static final int SIZE = 32;  // 当前类型所占bit[位]数
    
    /**
     * The number of bytes used to represent a {@code float} value.
     *
     * @since 1.8
     */
    public static final int BYTES = SIZE / Byte.SIZE;   // 当前类型所占字节数
    
    /**
     * The value of the Float.
     *
     * @serial
     */
    private final float value; // 当前类包装的值
    
    
    
    /*▼ 构造方法 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Constructs a newly allocated {@code Float} object that
     * represents the primitive {@code float} argument.
     *
     * @param value the value to be represented by the {@code Float}.
     *
     * @deprecated It is rarely appropriate to use this constructor. The static factory
     * {@link #valueOf(float)} is generally a better choice, as it is
     * likely to yield significantly better space and time performance.
     */
    @Deprecated(since = "9")
    public Float(float value) {
        this.value = value;
    }
    
    /**
     * Constructs a newly allocated {@code Float} object that
     * represents the argument converted to type {@code float}.
     *
     * @param value the value to be represented by the {@code Float}.
     *
     * @deprecated It is rarely appropriate to use this constructor. Instead, use the
     * static factory method {@link #valueOf(float)} method as follows:
     * {@code Float.valueOf((float)value)}.
     */
    @Deprecated(since = "9")
    public Float(double value) {
        this.value = (float) value;
    }
    
    /**
     * Constructs a newly allocated {@code Float} object that
     * represents the floating-point value of type {@code float}
     * represented by the string. The string is converted to a
     * {@code float} value as if by the {@code valueOf} method.
     *
     * @param s a string to be converted to a {@code Float}.
     *
     * @throws NumberFormatException if the string does not contain a
     *                               parsable number.
     * @deprecated It is rarely appropriate to use this constructor.
     * Use {@link #parseFloat(String)} to convert a string to a
     * {@code float} primitive, or use {@link #valueOf(String)}
     * to convert a string to a {@code Float} object.
     */
    @Deprecated(since = "9")
    public Float(String s) throws NumberFormatException {
        value = parseFloat(s);
    }
    
    /*▲ 构造方法 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ [装箱] ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns a {@code Float} instance representing the specified
     * {@code float} value.
     * If a new {@code Float} instance is not required, this method
     * should generally be used in preference to the constructor
     * {@link #Float(float)}, as this method is likely to yield
     * significantly better space and time performance by caching
     * frequently requested values.
     *
     * @param f a float value.
     *
     * @return a {@code Float} instance representing {@code f}.
     *
     * @since 1.5
     */
    // float-->Float 默认的装箱行为
    @HotSpotIntrinsicCandidate
    public static Float valueOf(float f) {
        return new Float(f);
    }
    
    /**
     * Returns a {@code Float} object holding the
     * {@code float} value represented by the argument string
     * {@code s}.
     *
     * <p>If {@code s} is {@code null}, then a
     * {@code NullPointerException} is thrown.
     *
     * <p>Leading and trailing whitespace characters in {@code s}
     * are ignored.  Whitespace is removed as if by the {@link
     * String#trim} method; that is, both ASCII space and control
     * characters are removed. The rest of {@code s} should
     * constitute a <i>FloatValue</i> as described by the lexical
     * syntax rules:
     *
     * <blockquote>
     * <dl>
     * <dt><i>FloatValue:</i>
     * <dd><i>Sign<sub>opt</sub></i> {@code NaN}
     * <dd><i>Sign<sub>opt</sub></i> {@code Infinity}
     * <dd><i>Sign<sub>opt</sub> FloatingPointLiteral</i>
     * <dd><i>Sign<sub>opt</sub> HexFloatingPointLiteral</i>
     * <dd><i>SignedInteger</i>
     * </dl>
     *
     * <dl>
     * <dt><i>HexFloatingPointLiteral</i>:
     * <dd> <i>HexSignificand BinaryExponent FloatTypeSuffix<sub>opt</sub></i>
     * </dl>
     *
     * <dl>
     * <dt><i>HexSignificand:</i>
     * <dd><i>HexNumeral</i>
     * <dd><i>HexNumeral</i> {@code .}
     * <dd>{@code 0x} <i>HexDigits<sub>opt</sub>
     * </i>{@code .}<i> HexDigits</i>
     * <dd>{@code 0X}<i> HexDigits<sub>opt</sub>
     * </i>{@code .} <i>HexDigits</i>
     * </dl>
     *
     * <dl>
     * <dt><i>BinaryExponent:</i>
     * <dd><i>BinaryExponentIndicator SignedInteger</i>
     * </dl>
     *
     * <dl>
     * <dt><i>BinaryExponentIndicator:</i>
     * <dd>{@code p}
     * <dd>{@code P}
     * </dl>
     *
     * </blockquote>
     *
     * where <i>Sign</i>, <i>FloatingPointLiteral</i>,
     * <i>HexNumeral</i>, <i>HexDigits</i>, <i>SignedInteger</i> and
     * <i>FloatTypeSuffix</i> are as defined in the lexical structure
     * sections of
     * <cite>The Java&trade; Language Specification</cite>,
     * except that underscores are not accepted between digits.
     * If {@code s} does not have the form of
     * a <i>FloatValue</i>, then a {@code NumberFormatException}
     * is thrown. Otherwise, {@code s} is regarded as
     * representing an exact decimal value in the usual
     * "computerized scientific notation" or as an exact
     * hexadecimal value; this exact numerical value is then
     * conceptually converted to an "infinitely precise"
     * binary value that is then rounded to type {@code float}
     * by the usual round-to-nearest rule of IEEE 754 floating-point
     * arithmetic, which includes preserving the sign of a zero
     * value.
     *
     * Note that the round-to-nearest rule also implies overflow and
     * underflow behaviour; if the exact value of {@code s} is large
     * enough in magnitude (greater than or equal to ({@link
     * #MAX_VALUE} + {@link Math#ulp(float) ulp(MAX_VALUE)}/2),
     * rounding to {@code float} will result in an infinity and if the
     * exact value of {@code s} is small enough in magnitude (less
     * than or equal to {@link #MIN_VALUE}/2), rounding to float will
     * result in a zero.
     *
     * Finally, after rounding a {@code Float} object representing
     * this {@code float} value is returned.
     *
     * <p>To interpret localized string representations of a
     * floating-point value, use subclasses of {@link
     * java.text.NumberFormat}.
     *
     * <p>Note that trailing format specifiers, specifiers that
     * determine the type of a floating-point literal
     * ({@code 1.0f} is a {@code float} value;
     * {@code 1.0d} is a {@code double} value), do
     * <em>not</em> influence the results of this method.  In other
     * words, the numerical value of the input string is converted
     * directly to the target floating-point type.  In general, the
     * two-step sequence of conversions, string to {@code double}
     * followed by {@code double} to {@code float}, is
     * <em>not</em> equivalent to converting a string directly to
     * {@code float}.  For example, if first converted to an
     * intermediate {@code double} and then to
     * {@code float}, the string<br>
     * {@code "1.00000017881393421514957253748434595763683319091796875001d"}<br>
     * results in the {@code float} value
     * {@code 1.0000002f}; if the string is converted directly to
     * {@code float}, <code>1.000000<b>1</b>f</code> results.
     *
     * <p>To avoid calling this method on an invalid string and having
     * a {@code NumberFormatException} be thrown, the documentation
     * for {@link Double#valueOf Double.valueOf} lists a regular
     * expression which can be used to screen the input.
     *
     * @param s the string to be parsed.
     *
     * @return a {@code Float} object holding the value
     * represented by the {@code String} argument.
     *
     * @throws NumberFormatException if the string does not contain a
     *                               parsable number.
     */
    // 将字符串s解析为float值，然后再装箱
    public static Float valueOf(String s) throws NumberFormatException {
        return new Float(parseFloat(s));
    }
    
    /*▲ [装箱] ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ [拆箱] ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns the value of this {@code Float} as a {@code byte} after
     * a narrowing primitive conversion.
     *
     * @return the {@code float} value represented by this object
     * converted to type {@code byte}
     *
     * @jls 5.1.3 Narrowing Primitive Conversions
     */
    // 以byte形式返回当前对象的值
    public byte byteValue() {
        return (byte) value;
    }
    
    /**
     * Returns the value of this {@code Float} as a {@code short}
     * after a narrowing primitive conversion.
     *
     * @return the {@code float} value represented by this object
     * converted to type {@code short}
     *
     * @jls 5.1.3 Narrowing Primitive Conversions
     * @since 1.1
     */
    // 以short形式返回当前对象的值
    public short shortValue() {
        return (short) value;
    }
    
    /**
     * Returns the value of this {@code Float} as an {@code int} after
     * a narrowing primitive conversion.
     *
     * @return the {@code float} value represented by this object
     * converted to type {@code int}
     *
     * @jls 5.1.3 Narrowing Primitive Conversions
     */
    // 以int形式返回当前对象的值
    public int intValue() {
        return (int) value;
    }
    
    /**
     * Returns value of this {@code Float} as a {@code long} after a
     * narrowing primitive conversion.
     *
     * @return the {@code float} value represented by this object
     * converted to type {@code long}
     *
     * @jls 5.1.3 Narrowing Primitive Conversions
     */
    // 以long形式返回当前对象的值
    public long longValue() {
        return (long) value;
    }
    
    /**
     * Returns the {@code float} value of this {@code Float} object.
     *
     * @return the {@code float} value represented by this object
     */
    // Float-->float 默认的拆箱行为
    @HotSpotIntrinsicCandidate
    public float floatValue() {
        return value;
    }
    
    /**
     * Returns the value of this {@code Float} as a {@code double}
     * after a widening primitive conversion.
     *
     * @return the {@code float} value represented by this
     * object converted to type {@code double}
     *
     * @jls 5.1.2 Widening Primitive Conversions
     */
    // 以double形式返回当前对象的值
    public double doubleValue() {
        return (double) value;
    }
    
    /*▲ [拆箱] ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 逆字符串化 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns a new {@code float} initialized to the value
     * represented by the specified {@code String}, as performed
     * by the {@code valueOf} method of class {@code Float}.
     *
     * @param s the string to be parsed.
     *
     * @return the {@code float} value represented by the string
     * argument.
     *
     * @throws NullPointerException  if the string is null
     * @throws NumberFormatException if the string does not contain a
     *                               parsable {@code float}.
     * @see java.lang.Float#valueOf(String)
     * @since 1.2
     */
    // 将字符串s解析为float值
    public static float parseFloat(String s) throws NumberFormatException {
        return FloatingDecimal.parseFloat(s);
    }
    
    /*▲ 逆字符串化 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 字符串化 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns a string representation of this {@code Float} object.
     * The primitive {@code float} value represented by this object
     * is converted to a {@code String} exactly as if by the method
     * {@code toString} of one argument.
     *
     * @return a {@code String} representation of this object.
     *
     * @see java.lang.Float#toString(float)
     */
    public String toString() {
        return Float.toString(value);
    }
    
    /**
     * Returns a string representation of the {@code float}
     * argument. All characters mentioned below are ASCII characters.
     * <ul>
     * <li>If the argument is NaN, the result is the string
     * "{@code NaN}".
     * <li>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
     * '{@code -}' ({@code '\u005Cu002D'}); if the sign is
     * positive, no sign character appears in the result. As for
     * the magnitude <i>m</i>:
     * <ul>
     * <li>If <i>m</i> is infinity, it is represented by the characters
     * {@code "Infinity"}; thus, positive infinity produces
     * the result {@code "Infinity"} and negative infinity
     * produces the result {@code "-Infinity"}.
     * <li>If <i>m</i> is zero, it is represented by the characters
     * {@code "0.0"}; thus, negative zero produces the result
     * {@code "-0.0"} and positive zero produces the result
     * {@code "0.0"}.
     * <li> If <i>m</i> is greater than or equal to 10<sup>-3</sup> but
     * less than 10<sup>7</sup>, then it is represented as the
     * integer part of <i>m</i>, in decimal form with no leading
     * zeroes, followed by '{@code .}'
     * ({@code '\u005Cu002E'}), followed by one or more
     * decimal digits representing the fractional part of
     * <i>m</i>.
     * <li> If <i>m</i> is less than 10<sup>-3</sup> or greater than or
     * equal to 10<sup>7</sup>, then it is represented in
     * so-called "computerized scientific notation." Let <i>n</i>
     * be the unique integer such that 10<sup><i>n</i> </sup>&le;
     * <i>m</i> {@literal <} 10<sup><i>n</i>+1</sup>; then let <i>a</i>
     * be the mathematically exact quotient of <i>m</i> and
     * 10<sup><i>n</i></sup> so that 1 &le; <i>a</i> {@literal <} 10.
     * The magnitude is then represented as the integer part of
     * <i>a</i>, as a single decimal digit, followed by
     * '{@code .}' ({@code '\u005Cu002E'}), followed by
     * decimal digits representing the fractional part of
     * <i>a</i>, followed by the letter '{@code E}'
     * ({@code '\u005Cu0045'}), followed by a representation
     * of <i>n</i> as a decimal integer, as produced by the
     * method {@link java.lang.Integer#toString(int)}.
     *
     * </ul>
     * </ul>
     * How many digits must be printed for the fractional part of
     * <i>m</i> or <i>a</i>? 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
     * {@code float}. That is, suppose that <i>x</i> is the
     * exact mathematical value represented by the decimal
     * representation produced by this method for a finite nonzero
     * argument <i>f</i>. Then <i>f</i> must be the {@code float}
     * value nearest to <i>x</i>; or, if two {@code float} values are
     * equally close to <i>x</i>, then <i>f</i> must be one of
     * them and the least significant bit of the significand of
     * <i>f</i> must be {@code 0}.
     *
     * <p>To create localized string representations of a floating-point
     * value, use subclasses of {@link java.text.NumberFormat}.
     *
     * @param f the float to be converted.
     *
     * @return a string representation of the argument.
     */
    public static String toString(float f) {
        return FloatingDecimal.toJavaFormatString(f);
    }
    
    /**
     * Returns a hexadecimal string representation of the
     * {@code float} argument. All characters mentioned below are
     * ASCII characters.
     *
     * <ul>
     * <li>If the argument is NaN, the result is the string
     * "{@code NaN}".
     * <li>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 '{@code -}'
     * ({@code '\u005Cu002D'}); if the sign is positive, no sign character
     * appears in the result. As for the magnitude <i>m</i>:
     *
     * <ul>
     * <li>If <i>m</i> is infinity, it is represented by the string
     * {@code "Infinity"}; thus, positive infinity produces the
     * result {@code "Infinity"} and negative infinity produces
     * the result {@code "-Infinity"}.
     *
     * <li>If <i>m</i> is zero, it is represented by the string
     * {@code "0x0.0p0"}; thus, negative zero produces the result
     * {@code "-0x0.0p0"} and positive zero produces the result
     * {@code "0x0.0p0"}.
     *
     * <li>If <i>m</i> is a {@code float} value with a
     * normalized representation, substrings are used to represent the
     * significand and exponent fields.  The significand is
     * represented by the characters {@code "0x1."}
     * followed by a lowercase hexadecimal representation of the rest
     * of the significand as a fraction.  Trailing zeros in the
     * hexadecimal representation are removed unless all the digits
     * are zero, in which case a single zero is used. Next, the
     * exponent is represented by {@code "p"} followed
     * by a decimal string of the unbiased exponent as if produced by
     * a call to {@link Integer#toString(int) Integer.toString} on the
     * exponent value.
     *
     * <li>If <i>m</i> is a {@code float} value with a subnormal
     * representation, the significand is represented by the
     * characters {@code "0x0."} followed by a
     * hexadecimal representation of the rest of the significand as a
     * fraction.  Trailing zeros in the hexadecimal representation are
     * removed. Next, the exponent is represented by
     * {@code "p-126"}.  Note that there must be at
     * least one nonzero digit in a subnormal significand.
     *
     * </ul>
     *
     * </ul>
     *
     * <table class="striped">
     * <caption>Examples</caption>
     * <thead>
     * <tr><th scope="col">Floating-point Value</th><th scope="col">Hexadecimal String</th>
     * </thead>
     * <tbody>
     * <tr><th scope="row">{@code 1.0}</th> <td>{@code 0x1.0p0}</td>
     * <tr><th scope="row">{@code -1.0}</th>        <td>{@code -0x1.0p0}</td>
     * <tr><th scope="row">{@code 2.0}</th> <td>{@code 0x1.0p1}</td>
     * <tr><th scope="row">{@code 3.0}</th> <td>{@code 0x1.8p1}</td>
     * <tr><th scope="row">{@code 0.5}</th> <td>{@code 0x1.0p-1}</td>
     * <tr><th scope="row">{@code 0.25}</th>        <td>{@code 0x1.0p-2}</td>
     * <tr><th scope="row">{@code Float.MAX_VALUE}</th>
     * <td>{@code 0x1.fffffep127}</td>
     * <tr><th scope="row">{@code Minimum Normal Value}</th>
     * <td>{@code 0x1.0p-126}</td>
     * <tr><th scope="row">{@code Maximum Subnormal Value}</th>
     * <td>{@code 0x0.fffffep-126}</td>
     * <tr><th scope="row">{@code Float.MIN_VALUE}</th>
     * <td>{@code 0x0.000002p-126}</td>
     * </tbody>
     * </table>
     *
     * @param f the {@code float} to be converted.
     *
     * @return a hex string representation of the argument.
     *
     * @author Joseph D. Darcy
     * @since 1.5
     */
    // 返回浮点值f的十六进制形式
    public static String toHexString(float f) {
        if(Math.abs(f)<Float.MIN_NORMAL && f != 0.0f) {// float subnormal
            // Adjust exponent to create subnormal double,
            // then replace subnormal double exponent with subnormal float exponent
            String s = Double.toHexString(
                Math.scalb((double) f,
                    /* -1022+126 */
                    Double.MIN_EXPONENT - Float.MIN_EXPONENT)
            );
            return s.replaceFirst("p-1022$", "p-126");
        } else { // double string will be the same as float string
            return Double.toHexString(f);
        }
    }
    
    /*▲ 字符串化 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 比较 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Compares the two specified {@code float} values. The sign
     * of the integer value returned is the same as that of the
     * integer that would be returned by the call:
     * <pre>
     *    new Float(f1).compareTo(new Float(f2))
     * </pre>
     *
     * @param f1 the first {@code float} to compare.
     * @param f2 the second {@code float} to compare.
     *
     * @return the value {@code 0} if {@code f1} is
     * numerically equal to {@code f2}; a value less than
     * {@code 0} if {@code f1} is numerically less than
     * {@code f2}; and a value greater than {@code 0}
     * if {@code f1} is numerically greater than
     * {@code f2}.
     *
     * @since 1.4
     */
    // 比较两个float
    public static int compare(float f1, float f2) {
        if(f1<f2)
            return -1;           // Neither val is NaN, thisVal is smaller
        if(f1>f2)
            return 1;            // Neither val is NaN, thisVal is larger
        
        // Cannot use floatToRawIntBits because of possibility of NaNs.
        int thisBits = Float.floatToIntBits(f1);
        int anotherBits = Float.floatToIntBits(f2);
        
        return (thisBits == anotherBits
            ? 0 // Values are equal
            : (thisBits<anotherBits
            ? -1  // (-0.0, 0.0) or (!NaN, NaN)
            : 1)  // (0.0, -0.0) or (NaN, !NaN)
        );
    }
    
    /**
     * Compares two {@code 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 ({@code <, <=, ==, >=, >}) when
     * applied to primitive {@code float} values:
     *
     * <ul><li>
     * {@code Float.NaN} is considered by this method to
     * be equal to itself and greater than all other
     * {@code float} values
     * (including {@code Float.POSITIVE_INFINITY}).
     * <li>
     * {@code 0.0f} is considered by this method to be greater
     * than {@code -0.0f}.
     * </ul>
     *
     * This ensures that the <i>natural ordering</i> of {@code Float}
     * objects imposed by this method is <i>consistent with equals</i>.
     *
     * @param anotherFloat the {@code Float} to be compared.
     *
     * @return the value {@code 0} if {@code anotherFloat} is
     * numerically equal to this {@code Float}; a value
     * less than {@code 0} if this {@code Float}
     * is numerically less than {@code anotherFloat};
     * and a value greater than {@code 0} if this
     * {@code Float} is numerically greater than
     * {@code anotherFloat}.
     *
     * @see Comparable#compareTo(Object)
     * @since 1.2
     */
    // 比较两个Float
    public int compareTo(Float anotherFloat) {
        return Float.compare(value, anotherFloat.value);
    }
    
    /*▲ 比较 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 位操作 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * 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.
     */
    // 先计算value的二进制格式，然后返回该二进制格式表示的int
    @HotSpotIntrinsicCandidate
    public static int floatToIntBits(float value) {
        if(!isNaN(value)) {
            return floatToRawIntBits(value);
        }
        
        return 0x7fc00000;
    }
    
    /**
     * 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.
     *
     * <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 the integer representing
     * the actual NaN value.  Unlike the {@code floatToIntBits}
     * method, {@code floatToRawIntBits} does not collapse all the
     * bit patterns encoding a NaN to a single "canonical"
     * NaN value.
     *
     * <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 floatToRawIntBits}.
     *
     * @param value a floating-point number.
     *
     * @return the bits that represent the floating-point number.
     *
     * @since 1.3
     */
    // 先计算value的二进制格式，然后返回该二进制格式表示的int
    @HotSpotIntrinsicCandidate
    public static native int floatToRawIntBits(float value);
    
    /**
     * Returns the {@code float} value corresponding to a given
     * bit representation.
     * The argument is considered to be a representation of a
     * floating-point value according to the IEEE 754 floating-point
     * "single format" bit layout.
     *
     * <p>If the argument is {@code 0x7f800000}, the result is positive
     * infinity.
     *
     * <p>If the argument is {@code 0xff800000}, the result is negative
     * infinity.
     *
     * <p>If the argument is any value in the range
     * {@code 0x7f800001} through {@code 0x7fffffff} or in
     * the range {@code 0xff800001} through
     * {@code 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 {@code Float.floatToRawIntBits} method.
     *
     * <p>In all other cases, let <i>s</i>, <i>e</i>, and <i>m</i> be three
     * values that can be computed from the argument:
     *
     * <blockquote><pre>{@code
     * int s = ((bits >> 31) == 0) ? 1 : -1;
     * int e = ((bits >> 23) & 0xff);
     * int m = (e == 0) ?
     *                 (bits & 0x7fffff) << 1 :
     *                 (bits & 0x7fffff) | 0x800000;
     * }</pre></blockquote>
     *
     * Then the floating-point result equals the value of the mathematical
     * expression <i>s</i>&middot;<i>m</i>&middot;2<sup><i>e</i>-150</sup>.
     *
     * <p>Note that this method may not be able to return a
     * {@code float} NaN with exactly same bit pattern as the
     * {@code int} argument.  IEEE 754 distinguishes between two
     * kinds of NaNs, quiet NaNs and <i>signaling NaNs</i>.  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 {@code intBitsToFloat} may
     * not be able to return a {@code float} with a signaling NaN
     * bit pattern.  Consequently, for some {@code int} values,
     * {@code floatToRawIntBits(intBitsToFloat(start))} may
     * <i>not</i> equal {@code 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.
     *
     * @param bits an integer.
     *
     * @return the {@code float} floating-point value with the same bit
     * pattern.
     */
    // 先计算bits的二进制格式，然后返回该二进制格式表示的float
    @HotSpotIntrinsicCandidate
    public static native float intBitsToFloat(int bits);
    
    /*▲ 位操作 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 简单运算 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Adds two {@code float} values together as per the + operator.
     *
     * @param a the first operand
     * @param b the second operand
     *
     * @return the sum of {@code a} and {@code b}
     *
     * @jls 4.2.4 Floating-Point Operations
     * @see java.util.function.BinaryOperator
     * @since 1.8
     */
    // 求和
    public static float sum(float a, float b) {
        return a + b;
    }
    
    /**
     * Returns the greater of two {@code float} values
     * as if by calling {@link Math#max(float, float) Math.max}.
     *
     * @param a the first operand
     * @param b the second operand
     *
     * @return the greater of {@code a} and {@code b}
     *
     * @see java.util.function.BinaryOperator
     * @since 1.8
     */
    // 最大值
    public static float max(float a, float b) {
        return Math.max(a, b);
    }
    
    /**
     * Returns the smaller of two {@code float} values
     * as if by calling {@link Math#min(float, float) Math.min}.
     *
     * @param a the first operand
     * @param b the second operand
     *
     * @return the smaller of {@code a} and {@code b}
     *
     * @see java.util.function.BinaryOperator
     * @since 1.8
     */
    // 最小值
    public static float min(float a, float b) {
        return Math.min(a, b);
    }
    
    /*▲ 简单运算 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 非常规数值 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns {@code true} if this {@code Float} value is a
     * Not-a-Number (NaN), {@code false} otherwise.
     *
     * @return {@code true} if the value represented by this object is
     * NaN; {@code false} otherwise.
     */
    // 判断当前float值是否为NaN
    public boolean isNaN() {
        return isNaN(value);
    }
    
    /**
     * Returns {@code true} if the specified number is a
     * Not-a-Number (NaN) value, {@code false} otherwise.
     *
     * @param v the value to be tested.
     *
     * @return {@code true} if the argument is NaN;
     * {@code false} otherwise.
     */
    // 判断f是否为NaN
    public static boolean isNaN(float v) {
        return (v != v);
    }
    
    /**
     * Returns {@code true} if this {@code Float} value is
     * infinitely large in magnitude, {@code false} otherwise.
     *
     * @return {@code true} if the value represented by this object is
     * positive infinity or negative infinity;
     * {@code false} otherwise.
     */
    // 判断当前float值是否为正无穷大/负无穷大
    public boolean isInfinite() {
        return isInfinite(value);
    }
    
    /**
     * Returns {@code true} if the specified number is infinitely
     * large in magnitude, {@code false} otherwise.
     *
     * @param v the value to be tested.
     *
     * @return {@code true} if the argument is positive infinity or
     * negative infinity; {@code false} otherwise.
     */
    // 判断v是否为正无穷大/负无穷大
    public static boolean isInfinite(float v) {
        return (v == POSITIVE_INFINITY) || (v == NEGATIVE_INFINITY);
    }
    
    /**
     * Returns {@code true} if the argument is a finite floating-point
     * value; returns {@code false} otherwise (for NaN and infinity
     * arguments).
     *
     * @param f the {@code float} value to be tested
     *
     * @return {@code true} if the argument is a finite
     * floating-point value, {@code false} otherwise.
     *
     * @since 1.8
     */
    // 判断f是否为有限值
    public static boolean isFinite(float f) {
        return Math.abs(f)<=Float.MAX_VALUE;
    }
    
    /*▲ 非常规数值 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /**
     * Returns a hash code for this {@code Float} object. The
     * result is the integer bit representation, exactly as produced
     * by the method {@link #floatToIntBits(float)}, of the primitive
     * {@code float} value represented by this {@code Float}
     * object.
     *
     * @return a hash code value for this object.
     */
    @Override
    public int hashCode() {
        return Float.hashCode(value);
    }
    
    /**
     * Returns a hash code for a {@code float} value; compatible with
     * {@code Float.hashCode()}.
     *
     * @param value the value to hash
     *
     * @return a hash code value for a {@code float} value.
     *
     * @since 1.8
     */
    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));
    }
    
}