Java学习——Integer



1、parseInt()  

String[] str = {"12","23","45"};
  int sum = 0;
  for(int i=0;i<str.length;i++){
   int myint = Integer.parseInt(str[i]);
   sum = sum+myint;
  }
  System.out.print("数组各元素之和是"+sum);

public static int parseInt(String s)                    throws NumberFormatException

Parses the string argument as a signed decimal integer. The characters in the string must all be decimal digits, except that the first character may be an ASCII minus sign'-' ('\u002D') to indicate a negative value or an ASCII plus sign'+' ('\u002B') to indicate a positive value. The resulting integer value is returned, exactly as if the argument and the radix 10 were given as arguments to theparseInt(java.lang.String, int) method.

Parameters:

s - a String containing the int representation to be parsed

Returns:

the integer value represented by the argument in decimal.

Throws:

NumberFormatException - if the string does not contain a parsable integer.

2、

  String str1 = Integer.toString(255);
  String str2 = Integer.toBinaryString(255);
  String str3 = Integer.toHexString(255);
  String str4 = Integer.toOctalString(255);
  System.out.print("256十进制、二进制、十六进制、八进制分别表示为："+str1+"、"+str2+"、"+str3+"、"+str4);

运行结果：

256十进制、二进制、十六进制、八进制分别表示为：255、11111111、ff、377

toString

public static String toString(int i,              int radix)

Returns a string representation of the first argument in the radix specified by the second argument.

If the radix is smaller than Character.MIN_RADIX or larger than Character.MAX_RADIX, then the radix 10 is used instead.

If the first argument is negative, the first element of the result is the ASCII minus character'-' ('\u002D'). If the first argument is not negative, no sign character appears in the result.

The remaining characters of the result represent the magnitude of the first argument. If the magnitude is zero, it is represented by a single zero character'0' ('\u0030'); otherwise, the first character of the representation of the magnitude will not be the zero character. The following ASCII characters are used as digits:

0123456789abcdefghijklmnopqrstuvwxyz

These are '\u0030' through '\u0039' and '\u0061' through'\u007A'. Ifradix is N, then the first N of these characters are used as radix-N digits in the order shown. Thus, the digits for hexadecimal (radix 16) are0123456789abcdef. If uppercase letters are desired, theString.toUpperCase() method may be called on the result:

Integer.toString(n, 16).toUpperCase()

Parameters:

i - an integer to be converted to a string.

radix - the radix to use in the string representation.

Returns:

a string representation of the argument in the specified radix.

See Also:

Character.MAX_RADIX,Character.MIN_RADIX

• toHexString

  public static String toHexString(int i)

  Returns a string representation of the integer argument as an unsigned integer in base 16.

  The unsigned integer value is the argument plus 2³² if the argument is negative; otherwise, it is equal to the argument. This value is converted to a string of ASCII digits in hexadecimal (base 16) with no extra leading 0s. If the unsigned magnitude is zero, it is represented by a single zero character'0' ('\u0030'); otherwise, the first character of the representation of the unsigned magnitude will not be the zero character. The following characters are used as hexadecimal digits:

  0123456789abcdef

  These are the characters '\u0030' through '\u0039' and '\u0061' through '\u0066'. If uppercase letters are desired, theString.toUpperCase() method may be called on the result:

  Integer.toHexString(n).toUpperCase()

  Parameters:

  i - an integer to be converted to a string.

  Returns:

  the string representation of the unsigned integer value represented by the argument in hexadecimal (base 16).

  Since:

  JDK1.0.2

• toOctalString

  public static String toOctalString(int i)

  Returns a string representation of the integer argument as an unsigned integer in base 8.

  The unsigned integer value is the argument plus 2³² if the argument is negative; otherwise, it is equal to the argument. This value is converted to a string of ASCII digits in octal (base 8) with no extra leading0s.

  If the unsigned magnitude is zero, it is represented by a single zero character'0' ('\u0030'); otherwise, the first character of the representation of the unsigned magnitude will not be the zero character. The following characters are used as octal digits:

  01234567

  These are the characters '\u0030' through '\u0037'.

  Parameters:

  i - an integer to be converted to a string.

  Returns:

  the string representation of the unsigned integer value represented by the argument in octal (base 8).

  Since:

  JDK1.0.2

• toBinaryString

  public static String toBinaryString(int i)

  Returns a string representation of the integer argument as an unsigned integer in base 2.

  The unsigned integer value is the argument plus 2³² if the argument is negative; otherwise it is equal to the argument. This value is converted to a string of ASCII digits in binary (base 2) with no extra leading0s. If the unsigned magnitude is zero, it is represented by a single zero character'0' ('\u0030'); otherwise, the first character of the representation of the unsigned magnitude will not be the zero character. The characters'0' ('\u0030') and '1' ('\u0031') are used as binary digits.

  Parameters:

  i - an integer to be converted to a string.

  Returns:

  the string representation of the unsigned integer value represented by the argument in binary (base 2).

  Since:

  JDK1.0.2

• toString

  public static String toString(int i)

  Returns a String object representing the specified integer. The argument is converted to signed decimal representation and returned as a string, exactly as if the argument and radix 10 were given as arguments to thetoString(int, int) method.

  Parameters:

  i - an integer to be converted.

  Returns:

  a string representation of the argument in base 10.