1. 简介
Long类封装了一个值long原始类型的一个对象。一个Long类型的对象包含一个字段的类型是long。此外，该类提供了一些方法处理long、String的相关的操作。
2. 源码
Long类中属性有：
- 实例变量
- 实例方法
- 类变量
- 类方法
- 静态内部类
- 构造器
(1) 实例变量：
- value：表示数值大小（final不可变）
private final long value;
(2) 实例方法：
- byteValue：返回截断的byte类型值
public byte byteValue() {
return (byte)value;
}
- shortValue：返回截断的short类型值
public short shortValue() {
return (short)value;
}
- intValue：返回int类型值
public int intValue() {
return value;
}
- longValue：返回long类型值
public long longValue() {
return (long)value;
}
- floatValue：返回float类型值
public float floatValue() {
return (float)value;
}
- doubleValue：返回double类型值
public double doubleValue() {
return (double)value;
}
- toString: 重写Object类的toString方法，这里调用了类方法toString，后面解释
public String toString() {
return toString(value);
}
- hashCode：返回hash值，调用静态方法hashCode，详解见类方法hashCode
@Override
public int hashCode() {
return Long.hashCode(value);
}
- equals：与其他对象比较大小（可以跟任何对象比较）
public boolean equals(Object obj) {
if (obj instanceof Long) {
return value == ((Long)obj).longValue();
}
return false;
}
- compareTo：与另一Long比较大小，返回-1,0,1
public int compareTo(Long anotherLong) {
return compare(this.value, anotherLong.value);
}
(3) 类变量：
- MIN_VALUE：Long最小值，为0x8000000000000000L
public static final int MIN_VALUE = 0x8000000000000000L;
- MAX_VALUE：Long最大值，为0x7fffffffffffffffL
public static final long MAX_VALUE = 0x7fffffffffffffffL;
- TYPE：对应的原始类的类型"long"
public static final Class<Long> TYPE = (Class<Long>) Class.getPrimitiveClass("long");
- SIZE：Long数值二进制占用bit数目，为64
public static final int SIZE = 64;
4.Bytes：Long数值二进制占用byte数目，为8
public static final int BYTES = SIZE / Byte.SIZE;
- serialVersionUID：序列版本号
private static final long serialVersionUID = 1360826667806852920L;
(4) 类方法：
- toString(long i)：返回数值为i的字符串，基数为10
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;
}
}
3.String toString(long i, int radix)：转换为String，基数为radix
Integer中有toUnsignedString0(int val, int shift)方法，思路类似
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));
}
- toUnsignedString0(long val, int shift)：将integer转换为无符号数的字符串形式
与Integer.toUnsignedString0(int val, int shift)类似
static String toUnsignedString0(long val, int shift) {
// assert shift > 0 && shift <=5 : "Illegal shift value";
int mag = Long.SIZE - Long.numberOfLeadingZeros(val);
int chars = Math.max(((mag + (shift - 1)) / shift), 1);
char[] buf = new char[chars];
formatUnsignedLong(val, shift, buf, 0, chars);
return new String(buf, true);
}
- toBinaryString(long i)：转换为二进制形式（补码）
看懂3中的toUnsignedString0方法，这个应该就比较简单
// 直接调用toUnsingedString0方法，radix为2，所以shift为1
public static String toBinaryString(long i) {
return toUnsignedString0(i, 1);
}
- toOctalString(longi)：转换为八进制形式（补码）
看懂3中的toUnsignedString0方法，这个应该就比较简单
// 直接调用toUnsignedString0方法，radix为8， 所以shift为3
public static String toOctalString(long i) {
return toUnsignedString0(i, 3);
}
- toHexString(long i)：转换为十六进制形式（补码）
看懂3中的toUnsignedString0方法，这个应该就比较简单
// 直接调用toUnsignedString0方法，radix为16， 所以shift为4
public static String toHexString(long i) {
return toUnsignedString0(i, 4);
}
- toUnsignedBigInteger(long i)：将i作为无符号long类型转换为BigInteger
private static BigInteger toUnsignedBigInteger(long i) {
if (i >= 0L)
return BigInteger.valueOf(i);
else {
int upper = (int) (i >>> 32);
int lower = (int) i;
// return (upper << 32) + lower
return (BigInteger.valueOf(Integer.toUnsignedLong(upper))).shiftLeft(32).
add(BigInteger.valueOf(Integer.toUnsignedLong(lower)));
}
}
- toUnsignedString(long i)：转换为long无符号字符串
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 toUnsignedString(long i, int radix) {
if (i >= 0)
return toString(i, radix);
else {
switch (radix) {
case 2:
return toBinaryString(i);
case 4:
return toUnsignedString0(i, 2);
case 8:
return toOctalString(i);
case 10:
/*
* We can get the effect of an unsigned division by 10
* on a long value by first shifting right, yielding a
* positive value, and then dividing by 5. This
* allows the last digit and preceding digits to be
* isolated more quickly than by an initial conversion
* to BigInteger.
*/
long quot = (i >>> 1) / 5;
long rem = i - quot * 10;
return toString(quot) + rem;
case 16:
return toHexString(i);
case 32:
return toUnsignedString0(i, 5);
default:
return toUnsignedBigInteger(i).toString(radix);
}
}
}
- parseLong(String s, int radix)：将String解析成long，基数为radix
思路同Integer.parseInt(String s, int radix)
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;
}
- parseLong(String s)：将String解析成long，基数为10
// 直接调用9中的方法parseLong(s, 10)
public static long parseLong(String s) throws NumberFormatException {
return parseLong(s, 10);
}
- parseUnsignedLong(String s, int radix)：将无符号类型数值的String转换为long，基数为radix
思路同Integer.parseUnsignedInt(String s, int radix)
public static long parseUnsignedLong(String s, int radix)
throws NumberFormatException {
if (s == null) {
throw new NumberFormatException("null");
}
int len = s.length();
if (len > 0) {
char firstChar = s.charAt(0);
if (firstChar == '-') {
throw new
NumberFormatException(String.format("Illegal leading minus sign " +
"on unsigned string %s.", s));
} else {
if (len <= 12 || // Long.MAX_VALUE in Character.MAX_RADIX is 13 digits
(radix == 10 && len <= 18) ) { // Long.MAX_VALUE in base 10 is 19 digits
return parseLong(s, radix);
}
// No need for range checks on len due to testing above.
long first = parseLong(s.substring(0, len - 1), radix);
int second = Character.digit(s.charAt(len - 1), radix);
if (second < 0) {
throw new NumberFormatException("Bad digit at end of " + s);
}
long result = first * radix + second;
if (compareUnsigned(result, first) < 0) {
/*
* The maximum unsigned value, (2^64)-1, takes at
* most one more digit to represent than the
* maximum signed value, (2^63)-1. Therefore,
* parsing (len - 1) digits will be appropriately
* in-range of the signed parsing. In other
* words, if parsing (len -1) digits overflows
* signed parsing, parsing len digits will
* certainly overflow unsigned parsing.
*
* The compareUnsigned check above catches
* situations where an unsigned overflow occurs
* incorporating the contribution of the final
* digit.
*/
throw new NumberFormatException(String.format("String value %s exceeds " +
"range of unsigned long.", s));
}
return result;
}
} else {
throw NumberFormatException.forInputString(s);
}
}
- parseUnsignedLong(String s)： 将无符号类型数值的String转换为long，基数为10
// 直接调用11中的parseUnsignedLong(String s, int radix)
public static long parseUnsignedLong(String s) throws NumberFormatException {
return parseUnsignedLong(s, 10);
}
- valueOf(String s, int radix)：同11中 parseInt(char ch, int radix)
public static Long valueOf(String s, int radix) throws NumberFormatException {
return Long.valueOf(parseLong(s, radix));
}
- valueOf(String s)：同12中 parseLong(char ch)
public static Long valueOf(String s) throws NumberFormatException
{
return Long.valueOf(parseLong(s, 10));
}
- valueOf(int i)：根据int值返回Integer对象，如果在缓存池中，会返回缓存池中的对象，否则new对象，返回对象。缓存池默认是缓存 -128 ~ 127 的Interger对象，具体见静态内部类IntegerCache。
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);
}
- hashCode()：重写hashCode，hash值，利用异或运算返回新的hashCode
public static int hashCode(long value) {
return (int)(value ^ (value >>> 32));
}
- decode(String nm)：解析字符串为Long，基数自动从字符串解析， 用于解析系统属性参数
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;
}
- getLong(String nm, Integer val)：从系统属性解析读取指定key的属性值v，失败返回默认val对象
public static Long getLong(String nm, Long val) {
String v = null;
try {
v = System.getProperty(nm);
} catch (IllegalArgumentException | NullPointerException e) {
}
if (v != null) {
try {
return Long.decode(v);
} catch (NumberFormatException e) {
}
}
return val;
}
- 从系统属性解析读取指定key的属性值v，失败返回默认值为val的Integer
public static Long getLong(String nm, long val) {
Long result = Long.getLong(nm, null);
return (result == null) ? Long.valueOf(val) : result;
}
- compare(long x, long y)：比较大小，返回值-1,0,1
public static int compare(long x, long y) {
return (x < y) ? -1 : ((x == y) ? 0 : 1);
}
- compareUnsigned(long x, long y)：比较无符号int的值大小
// 如果x，y 均为正数，谁值大，对应的无符号值也大
// 如果x，y 均为负数，谁值更小，加上MIN_VALUE越界更多，所以值越大
// 如果x，y 一正一负，负数+MIN_VALUE越界为正数，所以肯定负数大
public static int compareUnsigned(long x, long y) {
return compare(x + MIN_VALUE, y + MIN_VALUE);
}
- divideUnsigned(int dividend, int divisor) ：无符号int数值相除
public static long divideUnsigned(long dividend, long divisor) {
if (divisor < 0L) { // signed comparison
// Answer must be 0 or 1 depending on relative magnitude
// of dividend and divisor.
return (compareUnsigned(dividend, divisor)) < 0 ? 0L :1L;
}
if (dividend > 0) // Both inputs non-negative
return dividend/divisor;
else {
/*
* For simple code, leveraging BigInteger. Longer and faster
* code written directly in terms of operations on longs is
* possible; see "Hacker's Delight" for divide and remainder
* algorithms.
*/
return toUnsignedBigInteger(dividend).
divide(toUnsignedBigInteger(divisor)).longValue();
}
}
- divideUnsigned(long dividend, long divisor)：无符号除法
public static long divideUnsigned(long dividend, long divisor) {
if (divisor < 0L) { // signed comparison
// Answer must be 0 or 1 depending on relative magnitude
// of dividend and divisor.
return (compareUnsigned(dividend, divisor)) < 0 ? 0L :1L;
}
if (dividend > 0) // Both inputs non-negative
return dividend/divisor;
else {
/*
* For simple code, leveraging BigInteger. Longer and faster
* code written directly in terms of operations on longs is
* possible; see "Hacker's Delight" for divide and remainder
* algorithms.
*/
return toUnsignedBigInteger(dividend).
divide(toUnsignedBigInteger(divisor)).longValue();
}
}
- remainderUnsigned(long dividend, long divisor)：无符号long数值取余
public static long remainderUnsigned(long dividend, long divisor) {
if (dividend > 0 && divisor > 0) { // signed comparisons
return dividend % divisor;
} else {
if (compareUnsigned(dividend, divisor) < 0) // Avoid explicit check for 0 divisor
return dividend;
else
return toUnsignedBigInteger(dividend).
remainder(toUnsignedBigInteger(divisor)).longValue();
}
}
- highestOneBit(long i)：取数值对应二进制的最高位第一个1，然后其他位全设为0，返回这个值
同Integer.highestOneBit(int i)
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);
}
- lowestOneBit(long i)：取数值对应二进制的最低位第一个1，然后其他全设为0，返回这个值
同Integer.lowestOneBit(int i)
public static long lowestOneBit(long i) {
// HD, Section 2-1
return i & -i;
}
- numberOfLeadingZeros(long i)：补码对应前缀连续0的个数
同Integer.numberOfLeadingZeros(int i)
// 前缀0的个数，也就是找到最高位1的位置
// 通常我们获取最高位1用 去一位一位的找 的方法去做，这样遍历32次才可以
// 这里运用了二分的方式去搜索，log(N)内完成
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;
}
- numberOfTrailingZeros(long i)：补码对应后缀连续0的个
同25中 numberOfLeadingZeros(long i)的前缀连续0的个数求法
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);
}
- bitCount(long i)：计算二进制中1的个数
(同Integer.bitCount(int i))
这是比较巧妙一种方式，详解见https://www.jianshu.com/p/0d0439dc7c6d
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;
}
- rotateLeft(long i, int distance)：二进制按位左旋转
public static long rotateLeft(long i, int distance) {
return (i << distance) | (i >>> -distance);
}
- rotateRight(long i, int distance)：二进制按位右旋转
public static long rotateRight(long i, int distance) {
return (i >>> distance) | (i << -distance);
}
- reverse(long i)：二进制按位反转
（同Integer.reverse(int)）
非常巧妙一种方式，详解见https://www.jianshu.com/u/0e206eac3b5c
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;
}
- signum(int i)：正负号函数
public static int signum(int i) {
// HD, Section 2-7
return (i >> 31) | (-i >>> 31);
}
- reverseBytes(long i)：按字节反转
public static int signum(long i) {
// HD, Section 2-7
return (int) ((i >> 63) | (-i >>> 63));
}
(5) 构造器：
- Long(long value)：按long 构造
public Long(long value) {
this.value = value;
}
- Long(String s)：按String构造
public Long(String s) throws NumberFormatException {
this.value = parseLong(s, 10);
}
(6) 静态内部类：
- LongCache：Long缓存池
缓存-128到127的数值的Long对象，初始化类就new好了缓存对象
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);
}
}
其他
本人也是在慢慢学习中，如有错误还请原谅、敬请指出，谢谢！
