- public final class Long extends Number implements Comparable<Long> {
- public static final long MIN_VALUE = 0x8000000000000000L;//最大值为-2^63
- public static final long MAX_VALUE = 0x7fffffffffffffffL;//最小值为2^63-1
- 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;//Long中进制数出错时,不跑异常,而是默认为10进制
- if (radix == 10)
- return toString(i);
- char[] buf = new char[65];
- int charPos = 64;
- boolean negative = (i < 0);
- if (!negative) {//统一转换为负数进行操作
- 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) {//将Long转为16进制
- return toUnsignedString(i, 4);
- }
- public static String toOctalString(long i) {//将Long转为8进制
- return toUnsignedString(i, 3);
- }
- public static String toBinaryString(long i) {//将Long转为2进制
- 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)];//确定最后一位在进制中对应的值
- i >>>= shift;//右移赋值
- } while (i != 0);
- return new String(buf, charPos, (64 - charPos));
- }
- public static String toString(long i) {//与Integer的toString方法相同
- if (i == Long.MIN_VALUE)
- return "-9223372036854775808";//最小值特殊处理
- int size = (i < 0) ? stringSize(-i) + 1 : stringSize(i);//负数需要多一位用来放负号
- char[] buf = new char[size];
- getChars(i, size, buf);
- return new String(buf, true);
- }
- static void getChars(long i, int index, char[] buf) {//使用了与Integer相同的getChars方法,不再分析
- 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;
- }
- }
- static int stringSize(long x) {//展示Long的字符串长度
- long p = 10;
- for (int i=1; i<19; i++) {每次乘十进行比较
- 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);//转化为了负数进行计算,所以要用<号
- }
- 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 {//默认转成10进制
- 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 {//Long的默认缓存,-128~127,缓存模块与Integer相同
- 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) { //在缓存范围内则自动使用缓存中的值
- return LongCache.cache[(int)l + offset];
- }
- return new Long(l);
- }
- public static Long decode(String nm) throws NumberFormatException {//用于对未知进制的long型字符串进行解码,根据开头的进制符判断进制,再转换为Long
- 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() {//重写hashcode()方法,无符号右移32位后乘value本身
- return (int)(value ^ (value >>> 32));
- }
- public boolean equals(Object obj) {
- if (obj instanceof Long) {
- return value == ((Long)obj).longValue();//比较的是value的地址值,所以在缓存范围内的相等,缓存范围外的不等(两个对象指向同一个Long除外)
- }
- return false;
- }
- public static Long getLong(String nm) {//用于获取系统变量
- 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) {//由于实现了Comparable<Long>接口,所以需要实现compareTo方法
- 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) {//返回二进制最高位的1的值
- // HD, Figure 3-1
- i |= (i >> 1);//Long为64位,所以要右移1,2,4,8,16,32,得到一个连续0和连续1组成的二进制数
- i |= (i >> 2);
- i |= (i >> 4);
- i |= (i >> 8);
- i |= (i >> 16);
- i |= (i >> 32);
- return i - (i >>> 1);//i减去i>>>1,即只剩下i的最高位的1(i由两部分组成,前面全为0,后面全为1)
- }
- public static long lowestOneBit(long i) {//将i转为2进制返回最右边的1所对应的10进制数,如1100返回4,1000返回8
- // HD, Section 2-1
- return i & -i;
- }
- public static int numberOfLeadingZeros(long i) {//返回i的开头的0的个数
- // 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) {//最右边开始数,有几个连续的0
- // 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) {//将i转化为二进制,返回二进制数中1的个数
- // 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) {//左旋转i值,比如i=110011,distance=1,返回100111
- return (i << distance) | (i >>> -distance);
- }
- public static long rotateRight(long i, int distance) {//右旋转i值,原理同上
- return (i >>> distance) | (i << -distance);
- }
- public static long reverse(long i) {//全部反转
- // 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) {用于判断正负值
- // HD, Section 2-7
- return (int) ((i >> 63) | (-i >>> 63));
- }
- public static long reverseBytes(long i) {//将一个字节作为单位(8位)反转i,
- i = (i & 0x00ff00ff00ff00ffL) << 8 | (i >>> 8) & 0x00ff00ff00ff00ffL;
- return (i << 48) | ((i & 0xffff0000L) << 16) |
- ((i >>> 16) & 0xffff0000L) | (i >>> 48);
- }
- private static final long serialVersionUID = 4290774380558885855L;
- }
2.1Long源码分析
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