The Integer method is Java’s encapsulation of int. It caches the Integer values from -128 to 127, including the conversion of different cardinality numbers, the method of converting each data type to the changed data type, and provides methods for comparison, summarization, and minimization.
// 非java属性，由c实现，最小值-2^31（-2147483648）
@Native public static final int MIN_VALUE = 0x80000000;
// 非java属性，由c实现，最大值2^31-1（2147483647）
@Native public static final int MAX_VALUE = 0x7fffffff;
// 是int的class实例，静态常量，代表Integer的基本数据类型
@SuppressWarnings("unchecked")
public static final Class<Integer> TYPE = (Class<Integer>) Class.getPrimitiveClass("int");
// 静态常量数组，存储9个数字和26个小写字母，所有进制有可能用到表达数字的字符
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'
};
// 参数（int整数，字符串中使用的基数）
public static String toString(int i, int radix) {
// 基数范围，2和36之间，不在区间的默认10进制
if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
radix = 10;
// 10进制直接转换
if (radix == 10) {
return toString(i);
}
// 存放转换进制后的字符数组
char buf[] = new char[33];
//判断是否为负数
boolean negative = (i < 0);
// 将指针指向buf数组最后一位，以便存放字符
int charPos = 32;
// 先转成负数处理，因为负数范围比整数大一
if (!negative) {
i = -i;
}
// 用短除法转换进制
while (i <= -radix) {
// 赋值每次的余数
buf[charPos--] = digits[-(i % radix)];
i = i / radix;
}
// 除的最终余数赋值在最前面
buf[charPos] = digits[-i];
// 存储负数位
if (negative) {
buf[--charPos] = '-';
}
// 返回字符串
return new String(buf, charPos, (33 - charPos));
}
public static String toUnsignedString(int i, int radix) {
return Long.toUnsignedString(toUnsignedLong(i), radix);
}
public static String toHexString(int i) {
return toUnsignedString0(i, 4);
}
public static String toOctalString(int i) {
return toUnsignedString0(i, 3);
}
public static String toBinaryString(int i) {
return toUnsignedString0(i, 1);
}
private static String toUnsignedString0(int val, int shift) {
// assert shift > 0 && shift <=5 : "Illegal shift value";
int mag = Integer.SIZE - Integer.numberOfLeadingZeros(val);
int chars = Math.max(((mag + (shift - 1)) / shift), 1);
char[] buf = new char[chars];
formatUnsignedInt(val, shift, buf, 0, chars);
// Use special constructor which takes over "buf".
return new String(buf, true);
}
static int formatUnsignedInt(int val, int shift, char[] buf, int offset, int len) {
int charPos = len;
int radix = 1 << shift;
int mask = radix - 1;
do {
buf[offset + --charPos] = Integer.digits[val & mask];
val >>>= shift;
} while (val != 0 && charPos > 0);
return 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);
}
public static String toUnsignedString(int i) {
return Long.toString(toUnsignedLong(i));
}
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;
}
}
// 用于判断多少位的数组列表
final static int [] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999,
99999999, 999999999, Integer.MAX_VALUE };
// 将数字进行判断，最后得出多少位进行加1
static int stringSize(int x) {
for (int i=0; ; i++)
if (x <= sizeTable[i])
return i+1;
}
// 传参字符串数字，基数，将字符串转换为Integer
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.
*/
// 抛出异常
if (s == null) {
throw new NumberFormatException("null");
}
// 最小二进制
if (radix < Character.MIN_RADIX) {
throw new NumberFormatException("radix " + radix +
" less than Character.MIN_RADIX");
}
// 最大36进制
if (radix > Character.MAX_RADIX) {
throw new NumberFormatException("radix " + radix +
" greater than Character.MAX_RADIX");
}
// 返回结果
int result = 0;
// 正负数标识
boolean negative = false;
// 字符串数字长度
int i = 0, len = s.length();
// 定义比较的初始化值，用作判断
int limit = -Integer.MAX_VALUE;
int multmin;
int digit;
// 字符串数字长度大于0
if (len > 0) {
// 获取字符串第一个为符号
char firstChar = s.charAt(0);
// 判断是否是是非法字符
if (firstChar < '0') { // Possible leading "+" or "-"
// 为"-"号，标记符号，重新定义比较值
if (firstChar == '-') {
negative = true;
limit = Integer.MIN_VALUE;
} else if (firstChar != '+')
// 不等于“+-”的非法字符直接抛出异常
throw NumberFormatException.forInputString(s);
// 只有非法字符也抛出异常
if (len == 1) // Cannot have lone "+" or "-"
throw NumberFormatException.forInputString(s);
i++;
}
// 将最小值往右一位
multmin = limit / radix;
// 循环索引
while (i < len) {
// Accumulating negatively avoids surprises near MAX_VALUE
// 把字符转换成对应基数的数值
digit = Character.digit(s.charAt(i++),radix);
// 字符如果小于0，代表是非法字符
if (digit < 0) {
throw NumberFormatException.forInputString(s);
}
// 不能小于multmin，因为下面*进制就会超出范围了
if (result < multmin) {
throw NumberFormatException.forInputString(s);
}
// 左移一位，0的话直接为0
result *= radix;
// 如果值小于最小值加字符，防止下面减去超出范围
if (result < limit + digit) {
// 抛出非法字符异常
throw NumberFormatException.forInputString(s);
}
// 将上面的字符放进来
result -= digit;
}
} else {
throw NumberFormatException.forInputString(s);
}
// 授予数字的符号，计算的时候正数变成负数，负数变成正数
return negative ? result : -result;
}
// 默认采用10进制处理
public static int parseInt(String s) throws NumberFormatException {
return parseInt(s,10);
}
public static int parseUnsignedInt(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 <= 5 || // Integer.MAX_VALUE in Character.MAX_RADIX is 6 digits
(radix == 10 && len <= 9) ) { // Integer.MAX_VALUE in base 10 is 10 digits
return parseInt(s, radix);
} else {
long ell = Long.parseLong(s, radix);
if ((ell & 0xffff_ffff_0000_0000L) == 0) {
return (int) ell;
} else {
throw new
NumberFormatException(String.format("String value %s exceeds " +
"range of unsigned int.", s));
}
}
}
} else {
throw NumberFormatException.forInputString(s);
}
}
public static int parseUnsignedInt(String s) throws NumberFormatException {
return parseUnsignedInt(s, 10);
}
// 有问题抛出数字格式异常，传参字符串类型数字和基数
public static Integer valueOf(String s, int radix) throws NumberFormatException {
return Integer.valueOf(parseInt(s,radix));
}
// 有问题抛出数字格式异常，传参字符串类型数字，默认按10进制
public static Integer valueOf(String s) throws NumberFormatException {
return Integer.valueOf(parseInt(s, 10));
}
// Integer缓存类，缓存了-128到127的Integer值，遇到范围内的直接取值
private static class IntegerCache {
static final int low = -128;
static final int high;
static final Integer cache[];
// 静态代码块
static {
// hige默认是127，但可以通过jvm的一个参数扩展高值 java -Djava.lang.Integer.IntegerCache.high = xxxx Aclass.class
int h = 127;
String integerCacheHighPropValue =
sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
if (integerCacheHighPropValue != null) {
try {
int i = parseInt(integerCacheHighPropValue);
i = Math.max(i, 127);
// Maximum array size is Integer.MAX_VALUE
h = Math.min(i, Integer.MAX_VALUE - (-low) -1);
} catch( NumberFormatException nfe) {
// If the property cannot be parsed into an int, ignore it.
}
}
high = h;
// 定义cache数组
cache = new Integer[(high - low) + 1];
int j = low;
for(int k = 0; k < cache.length; k++)
// 直接给该范围内的数字对象化，所以该范围取的是一个对象，地址相同
cache[k] = new Integer(j++);
// 断言，如果high<127会出错终止程序运行并打印出来
// range [-128, 127] must be interned (JLS7 5.1.7)
assert IntegerCache.high >= 127;
}
private IntegerCache() {}
}
// 首先判断在不在缓存范围，在的话从缓存中取，不在的话创建一个新对象。
public static Integer valueOf(int i) {
if (i >= IntegerCache.low && i <= IntegerCache.high)
return IntegerCache.cache[i + (-IntegerCache.low)];
return new Integer(i);
}
private final int value;
// int构造函数
public Integer(int value) {
this.value = value;
}
// String构造函数
public Integer(String s) throws NumberFormatException {
this.value = parseInt(s, 10);
}
// 强制转换
public byte byteValue() {
return (byte)value;
}
// 强制转换
public short shortValue() {
return (short)value;
}
// 返回int值
public int intValue() {
return value;
}
// 强制转换
public long longValue() {
return (long)value;
}
// 强制转换
public float floatValue() {
return (float)value;
}
// 强制转换
public double doubleValue() {
return (double)value;
}
// 转String
public String toString() {
return toString(value);
}
@Override
public int hashCode() {
return Integer.hashCode(value);
}
// 重写hashcode
public static int hashCode(int value) {
return value;
}
// 比较相等方法
public boolean equals(Object obj) {
if (obj instanceof Integer) {
return value == ((Integer)obj).intValue();
}
return false;
}
// 传参nm返回指定名称的系统属性值
public static Integer getInteger(String nm) {
return getInteger(nm, null);
}
// 传参nm返回指定名称的系统属性值，如果为空，要初始化val为对象返回
public static Integer getInteger(String nm, int val) {
Integer result = getInteger(nm, null);
return (result == null) ? Integer.valueOf(val) : result;
}
// 根据nm返回指定名称的系统属性值，本方法是用来获取系统参数值
// java.version Java 运行时环境版本
// java.vendor Java 运行时环境供应商
// java.vendor.url Java 供应商的 URL
// java.home Java 安装目录
public static Integer getInteger(String nm, Integer val) {
String v = null;
try {
v = System.getProperty(nm);
} catch (IllegalArgumentException | NullPointerException e) {
}
if (v != null) {
try {
return Integer.decode(v);
} catch (NumberFormatException e) {
}
}
return val;
}
// 对数字进行解码（2、8、16进制）
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;
}
// 比较方法
public int compareTo(Integer anotherInteger) {
return compare(this.value, anotherInteger.value);
}
// 比较方法
public static int compare(int x, int y) {
return (x < y) ? -1 : ((x == y) ? 0 : 1);
}
public static int compareUnsigned(int x, int y) {
return compare(x + MIN_VALUE, y + MIN_VALUE);
}
public static long toUnsignedLong(int x) {
return ((long) x) & 0xffffffffL;
}
public static int divideUnsigned(int dividend, int divisor) {
// In lieu of tricky code, for now just use long arithmetic.
return (int)(toUnsignedLong(dividend) / toUnsignedLong(divisor));
}
public static int remainderUnsigned(int dividend, int divisor) {
// In lieu of tricky code, for now just use long arithmetic.
return (int)(toUnsignedLong(dividend) % toUnsignedLong(divisor));
}
@Native public static final int SIZE = 32;
public static final int BYTES = SIZE / Byte.SIZE;
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));
}
// 汇总
public static int sum(int a, int b) {
return a + b;
}
// 取最大值
public static int max(int a, int b) {
return Math.max(a, b);
}
// 取最小值
public static int min(int a, int b) {
return Math.min(a, b);
}
// 序列号id
@Native private static final long serialVersionUID = 1360826667806852920L;
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