java中封装类（二）

java中的数字类型包括 Byte,Short,Integer,Long,Float,Double.其中前四个是整数，后两个是浮点数。 在说java中数字类型之前先来看看它们统一的基类Number。

package java.lang;

public abstract class Number implements java.io.Serializable {

    public abstract int intValue();

    public abstract long longValue();

    public abstract float floatValue();

    public abstract double doubleValue();

    public byte byteValue() {
        return (byte)intValue();
    }

    public short shortValue() {
        return (short)intValue();
    }

    private static final long serialVersionUID = -8742448824652078965L;
}

代码并不复杂，从代码可以看出数字类型的封装类可以转化为任意数字类型，也就是说数字类型是可以相互转化的。

首先概括的说一下这六个类型都是数字类型，都包含了这四个静态字段，分别是

Size代表数据二进制位的长度，MAX_VALUE最大值,MIN_VALUE最小值，和TYPE对应的基元类型的Class

需要特别说明的是 TYPE虽然也是Class<Long>，但是它和 Long.class的Class不是同一个对象。因为java的泛型是伪泛型，<>中的类型，只是代表该类型的对象可以强转为<>中的类型。

package demo.nio;

public class NumberDemo {

    public static void main(String[] args) {

        System.out.println(Long.class.getName());//java.lang.Long
        System.out.println(Long.TYPE.getName());//long
    }

}

四个整型类型的数据中，Byte的Size是8，也就是一个字节，Short的SIZE是16，也就是两个字节，Integer是32也就是4个字节，Long的SIZE是64也就是8个字节,它们的最大，最小值随长度的大小而变化，长度越大，最大值越大，最小值越小。

package demo.nio;

public class NumberDemo {

    public static void main(String[] args) {
        System.out.println(Byte.MAX_VALUE);//
        System.out.println(Byte.MIN_VALUE);//-128

        System.out.println(Short.MAX_VALUE);//
        System.out.println(Short.MIN_VALUE);//-32768

        System.out.println(Integer.MAX_VALUE);//
        System.out.println(Integer.MIN_VALUE);//-2147483648

        System.out.println(Long.MAX_VALUE);//
        System.out.println(Long.MIN_VALUE);//-9223372036854775808
    }

}

先说Byte类型，Byte就是一个字节，代表8个二进制位。内部有一个value字段，用于存放装箱前的数据。而这个封装类的hashCode就是该value，数字类型都包含这样几个静态函数:

valueOf(XXX v)

valueOf(String s, int radix)

valueOf(String s)

parseXXX(String s)

parseXXX(String s, int radix)

decode(String nm)

其中Byte的parse和decode都是调用Integer的方法实现的。其中parse用于转化普通数字，decode用于转化 0xa之类的数字。

package java.lang;

public final class Byte extends Number implements Comparable<Byte> {

    public static final byte   MIN_VALUE = -128;

    public static final byte   MAX_VALUE = 127;

    public static final Class<Byte> TYPE = (Class<Byte>) Class.getPrimitiveClass("byte");

    public static String toString(byte b) {
        return Integer.toString((int)b, 10);
    }

    private static class ByteCache {
        private ByteCache(){}

        static final Byte cache[] = new Byte[-(-128) + 127 + 1];

        static {
            for(int i = 0; i < cache.length; i++)
                cache[i] = new Byte((byte)(i - 128));
        }
    }

    public static Byte valueOf(byte b) {
        final int offset = 128;
        return ByteCache.cache[(int)b + offset];
    }

    public static byte parseByte(String s, int radix)throws NumberFormatException {
        int i = Integer.parseInt(s, radix);
        if (i < MIN_VALUE || i > MAX_VALUE)
            throw new NumberFormatException(
                "Value out of range. Value:\"" + s + "\" Radix:" + radix);
        return (byte)i;
    }

    public static byte parseByte(String s) throws NumberFormatException {
        return parseByte(s, 10);
    }

    public static Byte valueOf(String s, int radix)
        throws NumberFormatException {
        return valueOf(parseByte(s, radix));
    }

    public static Byte valueOf(String s) throws NumberFormatException {
        return valueOf(s, 10);
    }

    public static Byte decode(String nm) throws NumberFormatException {
        int i = Integer.decode(nm);
        if (i < MIN_VALUE || i > MAX_VALUE)
            throw new NumberFormatException(
                    "Value " + i + " out of range from input " + nm);
        return valueOf((byte)i);
    }

    private final byte value;

    public Byte(byte value) {
        this.value = value;
    }

    public Byte(String s) throws NumberFormatException {
        this.value = parseByte(s, 10);
    }

    public byte byteValue() {
        return value;
    }

    public short shortValue() {
        return (short)value;
    }

    public int intValue() {
        return (int)value;
    }

    public long longValue() {
        return (long)value;
    }

    public float floatValue() {
        return (float)value;
    }

    public double doubleValue() {
        return (double)value;
    }

    public String toString() {
        return Integer.toString((int)value);
    }

    public int hashCode() {
        return (int)value;
    }

    public boolean equals(Object obj) {
        if (obj instanceof Byte) {
            return value == ((Byte)obj).byteValue();
        }
        return false;
    }

    public int compareTo(Byte anotherByte) {
        return compare(this.value, anotherByte.value);
    }

    public static int compare(byte x, byte y) {
        return x - y;
    }

    public static final int SIZE = 8;

    private static final long serialVersionUID = -7183698231559129828L;
}

因为数字类型都实现了Comparable接口，也就是说他是可比较的类型，对于Byte compare的实现就是简单的减去，除此之外还有个ByteCache，存放了-128~127的装箱类型的数组。

valueOf(byte b)返回的就是Cache中的数据。

package demo.nio;

public class NumberDemo {
    public static void main(String[] args) {
        System.out.println(Byte.valueOf((byte) 10));
        System.out.println(Byte.valueOf("10"));
        System.out.println(Byte.valueOf("10",10));
        System.out.println(Byte.parseByte("a",16));
        System.out.println(Byte.parseByte("10"));
        System.out.println(Byte.decode("10"));
        System.out.println(Byte.decode("0xa"));//
    }
}

Short和Byte类型基本相同，valueOf，parseXXX，decode也是调用的Integer实现的，不过这里多了一个，reverseBytes(short i)函数，该函数的功能是将short数据反转，就是后八位变成前8位，前八位变成后八位。

如：0x100，反转之后就是0x1,0xa00反转之后就是10

Integer类型相对于前边的两个数字类型就复杂的多

首先它实现了parseXXX函数，toString函数，其次它多了很多静态函数。

package java.lang;

import java.util.Properties;

public final class Integer extends Number implements Comparable<Integer> {

    public static final int   MIN_VALUE = 0x80000000;

    public static final int   MAX_VALUE = 0x7fffffff;

    public static final Class<Integer>  TYPE = (Class<Integer>) Class.getPrimitiveClass("int");

    final static char[] digits = {
        '0' , '1' , '2' , '3' , '4' , '5' ,
        '6' , '7' , '8' , '9' , 'a' , 'b' ,
        'c' , 'd' , 'e' , 'f' , 'g' , 'h' ,
        'i' , 'j' , 'k' , 'l' , 'm' , 'n' ,
        'o' , 'p' , 'q' , 'r' , 's' , 't' ,
        'u' , 'v' , 'w' , 'x' , 'y' , 'z'
    };

    public static String toString(int i, int radix) {

        if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
            radix = 10;

        /* Use the faster version */
        if (radix == 10) {
            return toString(i);
        }

        char buf[] = new char[33];
        boolean negative = (i < 0);
        int charPos = 32;

        if (!negative) {
            i = -i;
        }

        while (i <= -radix) {
            buf[charPos--] = digits[-(i % radix)];
            i = i / radix;
        }
        buf[charPos] = digits[-i];

        if (negative) {
            buf[--charPos] = '-';
        }

        return new String(buf, charPos, (33 - charPos));
    }

    public static String toHexString(int i) {
        return toUnsignedString(i, 4);
    }

    public static String toOctalString(int i) {
        return toUnsignedString(i, 3);
    }

    public static String toBinaryString(int i) {
        return toUnsignedString(i, 1);
    }

    /**
     * Convert the integer to an unsigned number.
     */
    private static String toUnsignedString(int i, int shift) {
        char[] buf = new char[32];
        int charPos = 32;
        int radix = 1 << shift;
        int mask = radix - 1;
        do {
            buf[--charPos] = digits[i & mask];
            i >>>= shift;
        } while (i != 0);

        return new String(buf, charPos, (32 - charPos));
    }

    final static char [] DigitTens = {
        '0', '0', '0', '0', '0', '0', '0', '0', '0', '0',
        '1', '1', '1', '1', '1', '1', '1', '1', '1', '1',
        '2', '2', '2', '2', '2', '2', '2', '2', '2', '2',
        '3', '3', '3', '3', '3', '3', '3', '3', '3', '3',
        '4', '4', '4', '4', '4', '4', '4', '4', '4', '4',
        '5', '5', '5', '5', '5', '5', '5', '5', '5', '5',
        '6', '6', '6', '6', '6', '6', '6', '6', '6', '6',
        '7', '7', '7', '7', '7', '7', '7', '7', '7', '7',
        '8', '8', '8', '8', '8', '8', '8', '8', '8', '8',
        '9', '9', '9', '9', '9', '9', '9', '9', '9', '9',
        } ;

    final static char [] DigitOnes = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        } ;

    public static String toString(int i) {
        if (i == Integer.MIN_VALUE)
            return "-2147483648";
        int size = (i < 0) ? stringSize(-i) + 1 : stringSize(i);
        char[] buf = new char[size];
        getChars(i, size, buf);
        return new String(buf, true);
    }

    static void getChars(int i, int index, char[] buf) {
        int q, r;
        int charPos = index;
        char sign = 0;

        if (i < 0) {
            sign = '-';
            i = -i;
        }

        // Generate two digits per iteration
        while (i >= 65536) {
            q = i / 100;
        // really: r = i - (q * 100);
            r = i - ((q << 6) + (q << 5) + (q << 2));
            i = q;
            buf [--charPos] = DigitOnes[r];
            buf [--charPos] = DigitTens[r];
        }

        // Fall thru to fast mode for smaller numbers
        // assert(i <= 65536, i);
        for (;;) {
            q = (i * 52429) >>> (16+3);
            r = i - ((q << 3) + (q << 1));  // r = i-(q*10) ...
            buf [--charPos] = digits [r];
            i = q;
            if (i == 0) break;
        }
        if (sign != 0) {
            buf [--charPos] = sign;
        }
    }

    final static int [] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999,
                                      99999999, 999999999, Integer.MAX_VALUE };

    // Requires positive x
    static int stringSize(int x) {
        for (int i=0; ; i++)
            if (x <= sizeTable[i])
                return i+1;
    }

    public static int parseInt(String s, int radix)throws NumberFormatException{
        /*
         * WARNING: This method may be invoked early during VM initialization
         * before IntegerCache is initialized. Care must be taken to not use
         * the valueOf method.
         */

        if (s == null) {
            throw new NumberFormatException("null");
        }

        if (radix < Character.MIN_RADIX) {
            throw new NumberFormatException("radix " + radix +
                                            " less than Character.MIN_RADIX");
        }

        if (radix > Character.MAX_RADIX) {
            throw new NumberFormatException("radix " + radix +
                                            " greater than Character.MAX_RADIX");
        }

        int result = 0;
        boolean negative = false;
        int i = 0, len = s.length();
        int limit = -Integer.MAX_VALUE;
        int multmin;
        int digit;

        if (len > 0) {
            char firstChar = s.charAt(0);
            if (firstChar < '0') { // Possible leading "+" or "-"
                if (firstChar == '-') {
                    negative = true;
                    limit = Integer.MIN_VALUE;
                } else if (firstChar != '+')
                    throw NumberFormatException.forInputString(s);

                if (len == 1) // Cannot have lone "+" or "-"
                    throw NumberFormatException.forInputString(s);
                i++;
            }
            multmin = limit / radix;
            while (i < len) {
                // Accumulating negatively avoids surprises near MAX_VALUE
                digit = Character.digit(s.charAt(i++),radix);
                if (digit < 0) {
                    throw NumberFormatException.forInputString(s);
                }
                if (result < multmin) {
                    throw NumberFormatException.forInputString(s);
                }
                result *= radix;
                if (result < limit + digit) {
                    throw NumberFormatException.forInputString(s);
                }
                result -= digit;
            }
        } else {
            throw NumberFormatException.forInputString(s);
        }
        return negative ? result : -result;
    }

    public static int parseInt(String s) throws NumberFormatException {
        return parseInt(s,10);
    }

    public static Integer valueOf(String s, int radix) throws NumberFormatException {
        return Integer.valueOf(parseInt(s,radix));
    }

    public static Integer valueOf(String s) throws NumberFormatException {
        return Integer.valueOf(parseInt(s, 10));
    }

    private static class IntegerCache {
        static final int low = -128;
        static final int high;
        static final Integer cache[];

        static {
            // high value may be configured by property
            int h = 127;
            String integerCacheHighPropValue =
                sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
            if (integerCacheHighPropValue != null) {
                int i = parseInt(integerCacheHighPropValue);
                i = Math.max(i, 127);
                // Maximum array size is Integer.MAX_VALUE
                h = Math.min(i, Integer.MAX_VALUE - (-low));
            }
            high = h;

            cache = new Integer[(high - low) + 1];
            int j = low;
            for(int k = 0; k < cache.length; k++)
                cache[k] = new Integer(j++);
        }

        private IntegerCache() {}
    }

    public static Integer valueOf(int i) {
        assert IntegerCache.high >= 127;
        if (i >= IntegerCache.low && i <= IntegerCache.high)
            return IntegerCache.cache[i + (-IntegerCache.low)];
        return new Integer(i);
    }

    private final int value;

    public Integer(int value) {
        this.value = value;
    }

    public Integer(String s) throws NumberFormatException {
        this.value = parseInt(s, 10);
    }

    public byte byteValue() {
        return (byte)value;
    }

    public short shortValue() {
        return (short)value;
    }

    public int intValue() {
        return value;
    }

    public long longValue() {
        return (long)value;
    }

    public float floatValue() {
        return (float)value;
    }

    public double doubleValue() {
        return (double)value;
    }

    public String toString() {
        return toString(value);
    }

    public int hashCode() {
        return value;
    }

    public boolean equals(Object obj) {
        if (obj instanceof Integer) {
            return value == ((Integer)obj).intValue();
        }
        return false;
    }

    public static Integer getInteger(String nm) {
        return getInteger(nm, null);
    }

    public static Integer getInteger(String nm, int val) {
        Integer result = getInteger(nm, null);
        return (result == null) ? Integer.valueOf(val) : result;
    }

    public static Integer getInteger(String nm, Integer val) {
        String v = null;
        try {
            v = System.getProperty(nm);
        } catch (IllegalArgumentException e) {
        } catch (NullPointerException e) {
        }
        if (v != null) {
            try {
                return Integer.decode(v);
            } catch (NumberFormatException e) {
            }
        }
        return val;
    }

    public static Integer decode(String nm) throws NumberFormatException {
        int radix = 10;
        int index = 0;
        boolean negative = false;
        Integer result;

        if (nm.length() == 0)
            throw new NumberFormatException("Zero length string");
        char firstChar = nm.charAt(0);
        // Handle sign, if present
        if (firstChar == '-') {
            negative = true;
            index++;
        } else if (firstChar == '+')
            index++;

        // Handle radix specifier, if present
        if (nm.startsWith("0x", index) || nm.startsWith("0X", index)) {
            index += 2;
            radix = 16;
        }
        else if (nm.startsWith("#", index)) {
            index ++;
            radix = 16;
        }
        else if (nm.startsWith("0", index) && nm.length() > 1 + index) {
            index ++;
            radix = 8;
        }

        if (nm.startsWith("-", index) || nm.startsWith("+", index))
            throw new NumberFormatException("Sign character in wrong position");

        try {
            result = Integer.valueOf(nm.substring(index), radix);
            result = negative ? Integer.valueOf(-result.intValue()) : result;
        } catch (NumberFormatException e) {
            // If number is Integer.MIN_VALUE, we'll end up here. The next line
            // handles this case, and causes any genuine format error to be
            // rethrown.
            String constant = negative ? ("-" + nm.substring(index))
                                       : nm.substring(index);
            result = Integer.valueOf(constant, radix);
        }
        return result;
    }

    public int compareTo(Integer anotherInteger) {
        return compare(this.value, anotherInteger.value);
    }

    public static int compare(int x, int y) {
        return (x < y) ? -1 : ((x == y) ? 0 : 1);
    }

    public static final int SIZE = 32;

    public static int highestOneBit(int i) {
        // HD, Figure 3-1
        i |= (i >>  1);
        i |= (i >>  2);
        i |= (i >>  4);
        i |= (i >>  8);
        i |= (i >> 16);
        return i - (i >>> 1);
    }

    public static int lowestOneBit(int i) {
        // HD, Section 2-1
        return i & -i;
    }

    public static int numberOfLeadingZeros(int i) {
        // HD, Figure 5-6
        if (i == 0)
            return 32;
        int n = 1;
        if (i >>> 16 == 0) { n += 16; i <<= 16; }
        if (i >>> 24 == 0) { n +=  8; i <<=  8; }
        if (i >>> 28 == 0) { n +=  4; i <<=  4; }
        if (i >>> 30 == 0) { n +=  2; i <<=  2; }
        n -= i >>> 31;
        return n;
    }

    public static int numberOfTrailingZeros(int i) {
        // HD, Figure 5-14
        int y;
        if (i == 0) return 32;
        int n = 31;
        y = i <<16; if (y != 0) { n = n -16; i = y; }
        y = i << 8; if (y != 0) { n = n - 8; i = y; }
        y = i << 4; if (y != 0) { n = n - 4; i = y; }
        y = i << 2; if (y != 0) { n = n - 2; i = y; }
        return n - ((i << 1) >>> 31);
    }

    public static int bitCount(int i) {
        // HD, Figure 5-2
        i = i - ((i >>> 1) & 0x55555555);
        i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
        i = (i + (i >>> 4)) & 0x0f0f0f0f;
        i = i + (i >>> 8);
        i = i + (i >>> 16);
        return i & 0x3f;
    }

    public static int rotateLeft(int i, int distance) {
        return (i << distance) | (i >>> -distance);
    }

    public static int rotateRight(int i, int distance) {
        return (i >>> distance) | (i << -distance);
    }

    public static int reverse(int i) {
        // HD, Figure 7-1
        i = (i & 0x55555555) << 1 | (i >>> 1) & 0x55555555;
        i = (i & 0x33333333) << 2 | (i >>> 2) & 0x33333333;
        i = (i & 0x0f0f0f0f) << 4 | (i >>> 4) & 0x0f0f0f0f;
        i = (i << 24) | ((i & 0xff00) << 8) |
            ((i >>> 8) & 0xff00) | (i >>> 24);
        return i;
    }

    public static int signum(int i) {
        // HD, Section 2-7
        return (i >> 31) | (-i >>> 31);
    }

    public static int reverseBytes(int i) {
        return ((i >>> 24)           ) |
               ((i >>   8) &   0xFF00) |
               ((i <<   8) & 0xFF0000) |
               ((i << 24));
    }

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 1360826667806852920L;
}

compare的实现是如果大于返回1，小于返回-1而不是简单的减。hashCode也是内部的value字段。而它的Cache就没有维护全部的数据而是-128-127，valueOf函数的操作是如果在这个范围内则返回cache中的值，否则new一个返回。

它的toString系列，比较复杂，toHexString 16进制 toOctalString 8进制 toBinaryString 2进制 toString转化为十进制，他还有一个重载版本toString(int i, int radix) 转化为指定进制。

parseXXX 系列 parseInt(String s)转化为10进制数据，parseInt(String s, int radix)转化为指定进制

highestOneBit,lowestOneBit 只保留最高位的1和最低位1的结果。

bitCount 二进制数据1的个数

numberOfLeadingZeros,numberOfTrailingZeros 开头和末尾0的个数

signum 如果大于0，返回1，小于返回-1，等于0返回0

reverseBytes反转数字，高位变低位，4到1位，3到二位，2到三位，1到四位

package demo.nio;

public class NumberDemo {
    public static void main(String[] args) {

        System.out.println(Integer.toBinaryString(255));
        System.out.println(Integer.toHexString(255));
        System.out.println(Integer.toOctalString(255));

        System.out.println(Integer.highestOneBit(-8));//-2147483648

        System.out.println(Integer.bitCount(255));//

        System.out.println(Integer.lowestOneBit(-8));//
        System.out.println(Integer.numberOfLeadingZeros(-8));//
        System.out.println(Integer.numberOfTrailingZeros(-8));//

        System.out.println(Integer.signum(100));//
        System.out.println(Integer.signum(-100));//-1
        System.out.println(Integer.signum(0));//

        System.out.println(Integer.toBinaryString(128));
        System.out.println(Integer.toBinaryString(Integer.reverseBytes(128)));
        System.out.println(Integer.reverseBytes(128));//
    }

}

Long和Integer功能就比较类似，只是因为Long是64位，所以所有的函数都要重新实现。

package java.lang;

public final class Long extends Number implements Comparable<Long> {

    public static final long MIN_VALUE = 0x8000000000000000L;

    public static final long MAX_VALUE = 0x7fffffffffffffffL;

    public static final Class<Long> TYPE = (Class<Long>) Class.getPrimitiveClass("long");

    public static String toString(long i, int radix) {
        if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
            radix = 10;
        if (radix == 10)
            return toString(i);
        char[] buf = new char[65];
        int charPos = 64;
        boolean negative = (i < 0);

        if (!negative) {
            i = -i;
        }

        while (i <= -radix) {
            buf[charPos--] = Integer.digits[(int)(-(i % radix))];
            i = i / radix;
        }
        buf[charPos] = Integer.digits[(int)(-i)];

        if (negative) {
            buf[--charPos] = '-';
        }

        return new String(buf, charPos, (65 - charPos));
    }

    public static String toHexString(long i) {
        return toUnsignedString(i, 4);
    }

    public static String toOctalString(long i) {
        return toUnsignedString(i, 3);
    }

    public static String toBinaryString(long i) {
        return toUnsignedString(i, 1);
    }

    private static String toUnsignedString(long i, int shift) {
        char[] buf = new char[64];
        int charPos = 64;
        int radix = 1 << shift;
        long mask = radix - 1;
        do {
            buf[--charPos] = Integer.digits[(int)(i & mask)];
            i >>>= shift;
        } while (i != 0);
        return new String(buf, charPos, (64 - charPos));
    }

    public static String toString(long i) {
        if (i == Long.MIN_VALUE)
            return "-9223372036854775808";
        int size = (i < 0) ? stringSize(-i) + 1 : stringSize(i);
        char[] buf = new char[size];
        getChars(i, size, buf);
        return new String(buf, true);
    }

    static void getChars(long i, int index, char[] buf) {
        long q;
        int r;
        int charPos = index;
        char sign = 0;

        if (i < 0) {
            sign = '-';
            i = -i;
        }

        // Get 2 digits/iteration using longs until quotient fits into an int
        while (i > Integer.MAX_VALUE) {
            q = i / 100;
            // really: r = i - (q * 100);
            r = (int)(i - ((q << 6) + (q << 5) + (q << 2)));
            i = q;
            buf[--charPos] = Integer.DigitOnes[r];
            buf[--charPos] = Integer.DigitTens[r];
        }

        // Get 2 digits/iteration using ints
        int q2;
        int i2 = (int)i;
        while (i2 >= 65536) {
            q2 = i2 / 100;
            // really: r = i2 - (q * 100);
            r = i2 - ((q2 << 6) + (q2 << 5) + (q2 << 2));
            i2 = q2;
            buf[--charPos] = Integer.DigitOnes[r];
            buf[--charPos] = Integer.DigitTens[r];
        }

        // Fall thru to fast mode for smaller numbers
        // assert(i2 <= 65536, i2);
        for (;;) {
            q2 = (i2 * 52429) >>> (16+3);
            r = i2 - ((q2 << 3) + (q2 << 1));  // r = i2-(q2*10) ...
            buf[--charPos] = Integer.digits[r];
            i2 = q2;
            if (i2 == 0) break;
        }
        if (sign != 0) {
            buf[--charPos] = sign;
        }
    }

    // Requires positive x
    static int stringSize(long x) {
        long p = 10;
        for (int i=1; i<19; i++) {
            if (x < p)
                return i;
            p = 10*p;
        }
        return 19;
    }

    public static long parseLong(String s, int radix)throws NumberFormatException{
        if (s == null) {
            throw new NumberFormatException("null");
        }

        if (radix < Character.MIN_RADIX) {
            throw new NumberFormatException("radix " + radix +
                                            " less than Character.MIN_RADIX");
        }
        if (radix > Character.MAX_RADIX) {
            throw new NumberFormatException("radix " + radix +
                                            " greater than Character.MAX_RADIX");
        }

        long result = 0;
        boolean negative = false;
        int i = 0, len = s.length();
        long limit = -Long.MAX_VALUE;
        long multmin;
        int digit;

        if (len > 0) {
            char firstChar = s.charAt(0);
            if (firstChar < '0') { // Possible leading "+" or "-"
                if (firstChar == '-') {
                    negative = true;
                    limit = Long.MIN_VALUE;
                } else if (firstChar != '+')
                    throw NumberFormatException.forInputString(s);

                if (len == 1) // Cannot have lone "+" or "-"
                    throw NumberFormatException.forInputString(s);
                i++;
            }
            multmin = limit / radix;
            while (i < len) {
                // Accumulating negatively avoids surprises near MAX_VALUE
                digit = Character.digit(s.charAt(i++),radix);
                if (digit < 0) {
                    throw NumberFormatException.forInputString(s);
                }
                if (result < multmin) {
                    throw NumberFormatException.forInputString(s);
                }
                result *= radix;
                if (result < limit + digit) {
                    throw NumberFormatException.forInputString(s);
                }
                result -= digit;
            }
        } else {
            throw NumberFormatException.forInputString(s);
        }
        return negative ? result : -result;
    }

    public static long parseLong(String s) throws NumberFormatException {
        return parseLong(s, 10);
    }

    public static Long valueOf(String s, int radix) throws NumberFormatException {
        return Long.valueOf(parseLong(s, radix));
    }

    public static Long valueOf(String s) throws NumberFormatException
    {
        return Long.valueOf(parseLong(s, 10));
    }

    private static class LongCache {
        private LongCache(){}

        static final Long cache[] = new Long[-(-128) + 127 + 1];

        static {
            for(int i = 0; i < cache.length; i++)
                cache[i] = new Long(i - 128);
        }
    }

    public static Long valueOf(long l) {
        final int offset = 128;
        if (l >= -128 && l <= 127) { // will cache
            return LongCache.cache[(int)l + offset];
        }
        return new Long(l);
    }

    public static Long decode(String nm) throws NumberFormatException {
        int radix = 10;
        int index = 0;
        boolean negative = false;
        Long result;

        if (nm.length() == 0)
            throw new NumberFormatException("Zero length string");
        char firstChar = nm.charAt(0);
        // Handle sign, if present
        if (firstChar == '-') {
            negative = true;
            index++;
        } else if (firstChar == '+')
            index++;

        // Handle radix specifier, if present
        if (nm.startsWith("0x", index) || nm.startsWith("0X", index)) {
            index += 2;
            radix = 16;
        }
        else if (nm.startsWith("#", index)) {
            index ++;
            radix = 16;
        }
        else if (nm.startsWith("0", index) && nm.length() > 1 + index) {
            index ++;
            radix = 8;
        }

        if (nm.startsWith("-", index) || nm.startsWith("+", index))
            throw new NumberFormatException("Sign character in wrong position");

        try {
            result = Long.valueOf(nm.substring(index), radix);
            result = negative ? Long.valueOf(-result.longValue()) : result;
        } catch (NumberFormatException e) {
            // If number is Long.MIN_VALUE, we'll end up here. The next line
            // handles this case, and causes any genuine format error to be
            // rethrown.
            String constant = negative ? ("-" + nm.substring(index))
                                       : nm.substring(index);
            result = Long.valueOf(constant, radix);
        }
        return result;
    }

    private final long value;

    public Long(long value) {
        this.value = value;
    }

    public Long(String s) throws NumberFormatException {
        this.value = parseLong(s, 10);
    }

    public byte byteValue() {
        return (byte)value;
    }

    public short shortValue() {
        return (short)value;
    }

    public int intValue() {
        return (int)value;
    }

    public long longValue() {
        return (long)value;
    }

    public float floatValue() {
        return (float)value;
    }

    public double doubleValue() {
        return (double)value;
    }

    public String toString() {
        return toString(value);
    }

    public int hashCode() {
        return (int)(value ^ (value >>> 32));
    }

    public boolean equals(Object obj) {
        if (obj instanceof Long) {
            return value == ((Long)obj).longValue();
        }
        return false;
    }

    public static Long getLong(String nm) {
        return getLong(nm, null);
    }

    public static Long getLong(String nm, long val) {
        Long result = Long.getLong(nm, null);
        return (result == null) ? Long.valueOf(val) : result;
    }

    public static Long getLong(String nm, Long val) {
        String v = null;
        try {
            v = System.getProperty(nm);
        } catch (IllegalArgumentException e) {
        } catch (NullPointerException e) {
        }
        if (v != null) {
            try {
                return Long.decode(v);
            } catch (NumberFormatException e) {
            }
        }
        return val;
    }

    public int compareTo(Long anotherLong) {
        return compare(this.value, anotherLong.value);
    }

    public static int compare(long x, long y) {
        return (x < y) ? -1 : ((x == y) ? 0 : 1);
    }

    public static final int SIZE = 64;

    public static long highestOneBit(long i) {
        // HD, Figure 3-1
        i |= (i >>  1);
        i |= (i >>  2);
        i |= (i >>  4);
        i |= (i >>  8);
        i |= (i >> 16);
        i |= (i >> 32);
        return i - (i >>> 1);
    }

    public static long lowestOneBit(long i) {
        // HD, Section 2-1
        return i & -i;
    }

    public static int numberOfLeadingZeros(long i) {
        // HD, Figure 5-6
         if (i == 0)
            return 64;
        int n = 1;
        int x = (int)(i >>> 32);
        if (x == 0) { n += 32; x = (int)i; }
        if (x >>> 16 == 0) { n += 16; x <<= 16; }
        if (x >>> 24 == 0) { n +=  8; x <<=  8; }
        if (x >>> 28 == 0) { n +=  4; x <<=  4; }
        if (x >>> 30 == 0) { n +=  2; x <<=  2; }
        n -= x >>> 31;
        return n;
    }

    public static int numberOfTrailingZeros(long i) {
        // HD, Figure 5-14
        int x, y;
        if (i == 0) return 64;
        int n = 63;
        y = (int)i; if (y != 0) { n = n -32; x = y; } else x = (int)(i>>>32);
        y = x <<16; if (y != 0) { n = n -16; x = y; }
        y = x << 8; if (y != 0) { n = n - 8; x = y; }
        y = x << 4; if (y != 0) { n = n - 4; x = y; }
        y = x << 2; if (y != 0) { n = n - 2; x = y; }
        return n - ((x << 1) >>> 31);
    }

     public static int bitCount(long i) {
        // HD, Figure 5-14
        i = i - ((i >>> 1) & 0x5555555555555555L);
        i = (i & 0x3333333333333333L) + ((i >>> 2) & 0x3333333333333333L);
        i = (i + (i >>> 4)) & 0x0f0f0f0f0f0f0f0fL;
        i = i + (i >>> 8);
        i = i + (i >>> 16);
        i = i + (i >>> 32);
        return (int)i & 0x7f;
     }

    public static long rotateLeft(long i, int distance) {
        return (i << distance) | (i >>> -distance);
    }

    public static long rotateRight(long i, int distance) {
        return (i >>> distance) | (i << -distance);
    }

    public static long reverse(long i) {
        // HD, Figure 7-1
        i = (i & 0x5555555555555555L) << 1 | (i >>> 1) & 0x5555555555555555L;
        i = (i & 0x3333333333333333L) << 2 | (i >>> 2) & 0x3333333333333333L;
        i = (i & 0x0f0f0f0f0f0f0f0fL) << 4 | (i >>> 4) & 0x0f0f0f0f0f0f0f0fL;
        i = (i & 0x00ff00ff00ff00ffL) << 8 | (i >>> 8) & 0x00ff00ff00ff00ffL;
        i = (i << 48) | ((i & 0xffff0000L) << 16) |
            ((i >>> 16) & 0xffff0000L) | (i >>> 48);
        return i;
    }

    public static int signum(long i) {
        // HD, Section 2-7
        return (int) ((i >> 63) | (-i >>> 63));
    }

    public static long reverseBytes(long i) {
        i = (i & 0x00ff00ff00ff00ffL) << 8 | (i >>> 8) & 0x00ff00ff00ff00ffL;
        return (i << 48) | ((i & 0xffff0000L) << 16) |
            ((i >>> 16) & 0xffff0000L) | (i >>> 48);
    }

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 4290774380558885855L;
}

Float,Double是浮点数，相较于整数就复杂的多，除了整数中几个静态字段外，它又多了很多静态字段

POSITIVE_INFINITY 正无穷 NEGATIVE_INFINITY 负无穷 NaN 非数字 MAX_EXPONENT 最大指数 MIN_EXPONENT 最小指数 NAN 非数字

所以浮点数都有两个函数，判断是否无穷大，是否非数字

Float的Size是32，Double是64

它的compare值得一提，public static native int floatToRawIntBits(float value); 是通过这个本地函数，转化为int来比较大小的。parseFloat和valueOf系列调用的是另一个包里的函数，

toString系列是调用Double小的toString

package java.lang;

import sun.misc.FloatingDecimal;
import sun.misc.FpUtils;
import sun.misc.FloatConsts;
import sun.misc.DoubleConsts;

public final class Float extends Number implements Comparable<Float> {

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

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

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

    public static final float MAX_VALUE = 0x1.fffffeP+127f; // 3.4028235e+38f

    public static final float MIN_NORMAL = 0x1.0p-126f; // 1.17549435E-38f

    public static final float MIN_VALUE = 0x0.000002P-126f; // 1.4e-45f

    public static final int MAX_EXPONENT = 127;

    public static final int MIN_EXPONENT = -126;

    public static final int SIZE = 32;

    public static final Class<Float> TYPE = Class.getPrimitiveClass("float");

    public static String toString(float f) {
        return new FloatingDecimal(f).toJavaFormatString();
    }

    public static String toHexString(float f) {
        if (Math.abs(f) < FloatConsts.MIN_NORMAL
            &&  f != 0.0f ) {// float subnormal
            String s = Double.toHexString(FpUtils.scalb((double)f,
                                                        /* -1022+126 */
                                                        DoubleConsts.MIN_EXPONENT-
                                                        FloatConsts.MIN_EXPONENT));
            return s.replaceFirst("p-1022$", "p-126");
        }
        else // double string will be the same as float string
            return Double.toHexString(f);
    }

    public static Float valueOf(String s) throws NumberFormatException {
        return new Float(FloatingDecimal.readJavaFormatString(s).floatValue());
    }

    public static Float valueOf(float f) {
        return new Float(f);
    }

    public static float parseFloat(String s) throws NumberFormatException {
        return FloatingDecimal.readJavaFormatString(s).floatValue();
    }

    static public boolean isNaN(float v) {
        return (v != v);
    }

    static public boolean isInfinite(float v) {
        return (v == POSITIVE_INFINITY) || (v == NEGATIVE_INFINITY);
    }

    private final float value;

    public Float(float value) {
        this.value = value;
    }

    public Float(double value) {
        this.value = (float)value;
    }

    public Float(String s) throws NumberFormatException {
        // REMIND: this is inefficient
        this(valueOf(s).floatValue());
    }

    public boolean isNaN() {
        return isNaN(value);
    }

    public boolean isInfinite() {
        return isInfinite(value);
    }

    public String toString() {
        return Float.toString(value);
    }

    public byte byteValue() {
        return (byte)value;
    }

    public short shortValue() {
        return (short)value;
    }

    public int intValue() {
        return (int)value;
    }

    public long longValue() {
        return (long)value;
    }

    public float floatValue() {
        return value;
    }

    public double doubleValue() {
        return (double)value;
    }

    public int hashCode() {
        return floatToIntBits(value);
    }

    public boolean equals(Object obj) {
        return (obj instanceof Float)
               && (floatToIntBits(((Float)obj).value) == floatToIntBits(value));
    }

    public static int floatToIntBits(float value) {
        int result = floatToRawIntBits(value);
        if ( ((result & FloatConsts.EXP_BIT_MASK) ==
              FloatConsts.EXP_BIT_MASK) &&
             (result & FloatConsts.SIGNIF_BIT_MASK) != 0)
            result = 0x7fc00000;
        return result;
    }

    public static native int floatToRawIntBits(float value);

    public static native float intBitsToFloat(int bits);

    public int compareTo(Float anotherFloat) {
        return Float.compare(value, anotherFloat.value);
    }

    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)
    }

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = -2671257302660747028L;
}

Double跟Float相比，就是实现了toString的一个函数，其余基本相似

package java.lang;

import sun.misc.FloatingDecimal;
import sun.misc.FpUtils;
import sun.misc.DoubleConsts;

public final class Double extends Number implements Comparable<Double> {

    public static final double POSITIVE_INFINITY = 1.0 / 0.0;

    public static final double NEGATIVE_INFINITY = -1.0 / 0.0;

    public static final double NaN = 0.0d / 0.0;

    public static final double MAX_VALUE = 0x1.fffffffffffffP+1023; // 1.7976931348623157e+308

    public static final double MIN_NORMAL = 0x1.0p-1022; // 2.2250738585072014E-308

    public static final double MIN_VALUE = 0x0.0000000000001P-1022; // 4.9e-324

    public static final int MAX_EXPONENT = 1023;

    public static final int MIN_EXPONENT = -1022;

    public static final int SIZE = 64;

    public static final Class<Double>   TYPE = (Class<Double>) Class.getPrimitiveClass("double");

    public static String toString(double d) {
        return new FloatingDecimal(d).toJavaFormatString();
    }

    public static String toHexString(double d) {
        /*
         * Modeled after the "a" conversion specifier in C99, section
         * 7.19.6.1; however, the output of this method is more
         * tightly specified.
         */
        if (!FpUtils.isFinite(d) )
            // For infinity and NaN, use the decimal output.
            return Double.toString(d);
        else {
            // Initialized to maximum size of output.
            StringBuffer answer = new StringBuffer(24);

            if (FpUtils.rawCopySign(1.0, d) == -1.0) // value is negative,
                answer.append("-");                  // so append sign info

            answer.append("0x");

            d = Math.abs(d);

            if(d == 0.0) {
                answer.append("0.0p0");
            }
            else {
                boolean subnormal = (d < DoubleConsts.MIN_NORMAL);

                // Isolate significand bits and OR in a high-order bit
                // so that the string representation has a known
                // length.
                long signifBits = (Double.doubleToLongBits(d)
                                   & DoubleConsts.SIGNIF_BIT_MASK) |
                    0x1000000000000000L;

                // Subnormal values have a 0 implicit bit; normal
                // values have a 1 implicit bit.
                answer.append(subnormal ? "0." : "1.");

                // Isolate the low-order 13 digits of the hex
                // representation.  If all the digits are zero,
                // replace with a single 0; otherwise, remove all
                // trailing zeros.
                String signif = Long.toHexString(signifBits).substring(3,16);
                answer.append(signif.equals("0000000000000") ? // 13 zeros
                              "0":
                              signif.replaceFirst("0{1,12}$", ""));

                // If the value is subnormal, use the E_min exponent
                // value for double; otherwise, extract and report d's
                // exponent (the representation of a subnormal uses
                // E_min -1).
                answer.append("p" + (subnormal ?
                               DoubleConsts.MIN_EXPONENT:
                               FpUtils.getExponent(d) ));
            }
            return answer.toString();
        }
    }

    public static Double valueOf(String s) throws NumberFormatException {
        return new Double(FloatingDecimal.readJavaFormatString(s).doubleValue());
    }

    public static Double valueOf(double d) {
        return new Double(d);
    }

    public static double parseDouble(String s) throws NumberFormatException {
        return FloatingDecimal.readJavaFormatString(s).doubleValue();
    }

    static public boolean isNaN(double v) {
        return (v != v);
    }

    static public boolean isInfinite(double v) {
        return (v == POSITIVE_INFINITY) || (v == NEGATIVE_INFINITY);
    }

    private final double value;

    public Double(double value) {
        this.value = value;
    }

    public Double(String s) throws NumberFormatException {
        // REMIND: this is inefficient
        this(valueOf(s).doubleValue());
    }

    public boolean isNaN() {
        return isNaN(value);
    }

    public boolean isInfinite() {
        return isInfinite(value);
    }

    public String toString() {
        return toString(value);
    }

    public byte byteValue() {
        return (byte)value;
    }

    public short shortValue() {
        return (short)value;
    }

    public int intValue() {
        return (int)value;
    }

    public long longValue() {
        return (long)value;
    }

    public float floatValue() {
        return (float)value;
    }

    public double doubleValue() {
        return (double)value;
    }

    public int hashCode() {
        long bits = doubleToLongBits(value);
        return (int)(bits ^ (bits >>> 32));
    }

    public boolean equals(Object obj) {
        return (obj instanceof Double)
               && (doubleToLongBits(((Double)obj).value) ==
                      doubleToLongBits(value));
    }

    public static long doubleToLongBits(double value) {
        long result = doubleToRawLongBits(value);
        // Check for NaN based on values of bit fields, maximum
        // exponent and nonzero significand.
        if ( ((result & DoubleConsts.EXP_BIT_MASK) ==
              DoubleConsts.EXP_BIT_MASK) &&
             (result & DoubleConsts.SIGNIF_BIT_MASK) != 0L)
            result = 0x7ff8000000000000L;
        return result;
    }

    public static native long doubleToRawLongBits(double value);

    public static native double longBitsToDouble(long bits);

    public int compareTo(Double anotherDouble) {
        return Double.compare(value, anotherDouble.value);
    }

    public static int compare(double d1, double d2) {
        if (d1 < d2)
            return -1;           // Neither val is NaN, thisVal is smaller
        if (d1 > d2)
            return 1;            // Neither val is NaN, thisVal is larger

        // Cannot use doubleToRawLongBits because of possibility of NaNs.
        long thisBits    = Double.doubleToLongBits(d1);
        long anotherBits = Double.doubleToLongBits(d2);

        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)
    }

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = -9172774392245257468L;
}