java二进制、八进制、十六进制间转换详细

转载自：http://blog.csdn.net/u010137760/article/details/52610442

1.各进制表示

java里不能使用前置表示2进制，只能是 8，10，16进制
8：前置 0
10：不需前置
16：前置 0x 或者 0X

public class test {public static void main(String[] args) {int octalB = 012;int hexB = 0x12;System.out.println(octalB);System.out.println(hexB);}
}

输出结果

8进制012->10进制10
16进制0x12->10进制18

2.转换-Integer.toBinaryString

测试代码

public class test {public static void main(String[] args) {//8进制、10进制、16进制转为2进制System.out.println("Integer.toBinaryString(01)="+Integer.toBinaryString(01));System.out.println("Integer.toBinaryString(012)="+Integer.toBinaryString(012));System.out.println("Integer.toBinaryString(10)="+Integer.toBinaryString(10));System.out.println("Integer.toBinaryString(0xa)="+Integer.toBinaryString(0xa));System.out.println("Integer.toOctalString(0x12)="+Integer.toOctalString(0x12));System.out.println("Integer.toOctalString(18)="+Integer.toOctalString(18));System.out.println("Integer.toHexString(012)="+Integer.toHexString(012));System.out.println("Integer.toHexString(10)="+Integer.toHexString(10));}
}

测试结果

Integer.toBinaryString(01)=1
Integer.toBinaryString(012)=1010
Integer.toBinaryString(10)=1010
Integer.toBinaryString(0xa)=1010
Integer.toOctalString(0x12)=22
Integer.toOctalString(18)=22
Integer.toHexString(012)=a
Integer.toHexString(10)=a

源码

toBinaryString、toOctalString、toHexString都类似，则以toBinaryString为例讲解
Integer.java

/*** Converts the specified integer into its binary string representation. * 将指定的整型转换为二进制表示* The returned string is a concatenation of '0' and '1' characters.* 返回的字符串是以'0'、'1'连接的* @param i  the integer to convert.要转换的整型值* @return the binary string representation of {@code i}.* 返回的二进制字符串*/
public static String toBinaryString(int i) {return IntegralToString.intToBinaryString(i);
}

IntegralToString.java

/*** The digits for every supported radix.*/
private static final 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 intToBinaryString(int i) {int bufLen = 32;  // 整型是4个字节32位char[] buf = new char[bufLen];int cursor = bufLen;do {buf[--cursor] = DIGITS[i & 1];}  while ((i >>>= 1) != 0);return new String(cursor, bufLen - cursor, buf);
}

运行过程

    当i=1时i = 1, cursor = 32doi&1=1,buf[31] = DIGITS[1] = 1whilei = 1>>>1 = 0,i == 0终止00000000 00000000 00000000 00000001----------------------------------------- 当i=2时i = 2(10), cursor = 32doi&1=0,buf[31] = DIGITS[0] = 0whilei = 2>>>1 = 1,i != 0成立doi&1=1,buf[30] = DIGITS[1] = 1whilei = 1>>>1 = 0,i == 0终止00000000 00000000 00000000 00000010

3.转换-Integer.valueOf

测试代码

public class test {public static void main(String[] args) {//十六进制转成十进制System.out.println(Integer.valueOf("FFFF",16));System.out.println(Integer.valueOf("-FFFF",16));//八进制转成十进制System.out.println(Integer.valueOf("776",8));System.out.println(Integer.valueOf("-776",8));//二进制转十进制System.out.println(Integer.valueOf("0101",2));System.out.println(Integer.valueOf("-0101",2));}
}

测试结果

源码

Integer.java

方法:valueOf

/*** Parses the specified string as a signed integer value using the specified radix.* 将制定的字符串转换为有符号的整数，参考指定的基数* @param string  the string representation of an integer value.* 字符串表示的整型值* @param radix   the radix to use when parsing.* 转换时指定基数，比如2代表2进制,8代表8进制,16代表16进制* @return an {@code Integer} instance containing the integer value*         represented by {@code string} using {@code radix}.* 整形值被转换为指定的基数的字符串* @throws NumberFormatException*             if {@code string} cannot be parsed as an integer value, or*             {@code radix < Character.MIN_RADIX ||*             radix > Character.MAX_RADIX}.* string不是整形值；radix< Character.MIN_RADIX或radix > Character.MAX_RADIX都会报转换异常* @see #parseInt(String, int)*/public static Integer valueOf(String string, int radix) throws NumberFormatException {return valueOf(parseInt(string, radix));}

方法：parseInt

/*** The minimum radix used for conversions between characters and integers.*/
public static final int MIN_RADIX = 2;/*** The maximum radix used for conversions between characters(字符) and integers.(整型)*/
public static final int MAX_RADIX = 36;/*** Parses the specified string as a signed integer value using the specified radix. * The ASCII characters \u002d ('-') and \u002b ('+') are recognized as the minus and plus signs.* ASCII字符"-"和"+"被作为正负号*/public static int parseInt(String string, int radix) throws NumberFormatException {if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) {throw new NumberFormatException("Invalid radix: " + radix);}if (string == null || string.isEmpty()) {throw invalidInt(string);//返回的是一个NumberFormatException异常}char firstChar = string.charAt(0);//如果字符串以'-'或'+'开头，则firstDigitIndex = 1作为后续操作的标识int firstDigitIndex = (firstChar == '-' || firstChar == '+') ? 1 : 0;//字符串只有'-'或'+'抛异常if (firstDigitIndex == string.length()) {throw invalidInt(string);}return parse(string, firstDigitIndex, radix, firstChar == '-');}

方法：parse

/*** Constant for the minimum {@code int} value, -2<sup>31</sup>.*/
public static final int MIN_VALUE = 0x80000000;
private static int parse(String string, int offset, int radix, boolean negative) throws NumberFormatException {int max = Integer.MIN_VALUE / radix;int result = 0;int length = string.length();while (offset < length) {int digit = Character.digit(string.charAt(offset++), radix);if (digit == -1) {throw invalidInt(string);}if (max > result) {throw invalidInt(string);}int next = result * radix - digit;if (next > result) {throw invalidInt(string);}result = next;}//negative以'-'开头则为trueif (!negative) {//以'+'开头result = -result;if (result < 0) {throw invalidInt(string);}}return result;
}

Character.java
方法：digit

public static int digit(char c, int radix) {return digit((int) c, radix);
}/*** Convenience method to determine the value of the character* {@code codePoint} in the supplied radix. The value of {@code radix} must* be between MIN_RADIX and MAX_RADIX.* 基于radix来确定codePoint指定的字符，radix必须在MIN_RADIX与MAX_RADIX之间* @param codePoint  the character, including supplementary characters.* @return if {@code radix} lies between {@link #MIN_RADIX} and*         {@link #MAX_RADIX} then the value of the character in the radix;*         -1 otherwise.*/
public static int digit(int codePoint, int radix) {//1,2//在最大与最小之间，否则返回-1if (radix < MIN_RADIX || radix > MAX_RADIX) {return -1;}if (codePoint < 128) {// Optimized for ASCIIint result = -1;if ('0' <= codePoint && codePoint <= '9') {result = codePoint - '0';} else if ('a' <= codePoint && codePoint <= 'z') {result = 10 + (codePoint - 'a');} else if ('A' <= codePoint && codePoint <= 'Z') {result = 10 + (codePoint - 'A');}return result < radix ? result : -1;}//当前类的native方法return digitImpl(codePoint, radix);
}private static native int digitImpl(int codePoint, int radix);