文章目录
1.概述
Integer是int的包装类,最大值为2^31-1 ,最小值为-2^31。Integer类主要的作用就是对基本类型int进行封装,提供了一些处理int类型的方法。
2.类图
和其他包装类一样,
继承了Number,实现了数值类型转换的方法
实现了Comparabel接口对Float对象进行比较
实现了Serializable序列化接口
3.属性
静态常量
@Native public static final int MIN_VALUE = 0x80000000;//最小值 因为是补码表示的,转换成原码就是 首位不变其他位取反+1,得到最小值。
@Native public static final int MAX_VALUE = 0x7fffffff;//最大值
public static final Class<Integer> TYPE = (Class<Integer>) Class.getPrimitiveClass("int"); // Integer.class
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'
};//对应着各个进制数字的符号表示
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',
} ;
final static int [] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999,99999999, 999999999, Integer.MAX_VALUE };//用于求Integer数的长度
@Native public static final int SIZE = 32;//占32位
public static final int BYTES = SIZE / Byte.SIZE; // 4个字节
@Native private static final long serialVersionUID = 1360826667806852920L;//序列化版本id
私有常量
private final int value;//final修饰不可变
4.构造方法
将int包装成Integer
public Integer(int value) {
this.value = value;
}
String 解析成10进制的int 然后包装成Integer
public Integer(String s) throws NumberFormatException {
this.value = parseInt(s, 10);
}
5.缓存
将数值-128到127都封装成对象 保存在一个cache数组中
最小值不能改变 最大值可以根据调整虚拟机参数来修改
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) {
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;
cache = new Integer[(high - low) + 1];
int j = low;
for(int k = 0; k < cache.length; k++)
cache[k] = new Integer(j++);
// range [-128, 127] must be interned (JLS7 5.1.7)
assert IntegerCache.high >= 127;
}
private IntegerCache() {}
}
6.toXXXString
- toString(int i, int radix) 根据进制数转换成String表达
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 toString(int i) {//将数字的每一位都存在buf数组中,将char数组转成String返回
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 String toString() {
return toString(value);
}
- toUnsignedString(int i)
public static String toUnsignedString(int i) {//将转换后的无符号数转成String返回
return Long.toString(toUnsignedLong(i));
}
public static long toUnsignedLong(int x) {//转成无符号的long型 高32位全0,低32位就是原来x的二进制表达。
return ((long) x) & 0xffffffffL;
}
- toHexString(int i) 将int转换成16进制的数 并返回String类型的表达
public static String toHexString(int i) {
return toUnsignedString0(i, 4);
}
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);
}
- toOctalString(int i) 将int转换成8进制的数 并返回String类型的表达
public static String toOctalString(int i) {
return toUnsignedString0(i, 3);
}
- toBinaryString(int i) 将int转换成2进制的数 并返回String类型的表达.负数其实就是得到补码的表达
public static String toBinaryString(int i) {
return toUnsignedString0(i, 1);
}
7. 求Integer数值的长度
前面提到的静态常量中的sizeTable就是用来帮助求出Integer数值的长度的。
static int stringSize(int x) {
for (int i=0; ; i++)
if (x <= sizeTable[i])
return i+1;
}
8.parseXXX
- parseInt(String s, int radix) 将字符串按照给定的进制数转换成int
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;
}
- parseInt(String s) 默认将其转换成10进制的int返回
public static int parseInt(String s) throws NumberFormatException {
return parseInt(s,10);
}
- parseUnsignedInt(String s, int radix) 将字符串按照给定的进制数转换成无符号int ,不能传入“-xxx”会报错
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);
}
}
- parseUnsignedInt(String s) 默认转换成10进制
public static int parseUnsignedInt(String s) throws NumberFormatException {
return parseUnsignedInt(s, 10);
}
9.valueOf
将int封装成Integer -128~127的值直接从缓存中返回对象,否则就是新构建一个Integer。自动封装的实现就是调用valueOf方法
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));
}
public static Integer valueOf(int i) {
if (i >= IntegerCache.low && i <= IntegerCache.high)
return IntegerCache.cache[i + (-IntegerCache.low)];
return new Integer(i);
}
10.XXXValue 转换成其他类型的数值返回
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;
}
11.hashCode
Integer的hashCode就等于其封装的int值
@Override
public int hashCode() {
return Integer.hashCode(value);
}
public static int hashCode(int value) {
return value;
}
12.其他方法
i的2进制表示中 末尾有多少个0
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);
}
i的2进制表示中 前面有多少个0
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;
}
2进制中 1的个数
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;
}
旋转
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);
}
翻转
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;
}
返回符号. 1表示正数 -1表示负数 i=0 返回0
public static int signum(int i) {
// HD, Section 2-7
return (i >> 31) | (-i >>> 31);
}