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小百科  ›  Integer (Java Platform SE 7 )
string
爱听歌的草稿本
1 年前
extends Number implements Comparable < Integer >
The Integer class wraps a value of the primitive type int in an object. An object of type Integer contains a single field whose type is int .

In addition, this class provides several methods for converting an int to a String and a String to an int , as well as other constants and methods useful when dealing with an int .

Implementation note: The implementations of the "bit twiddling" methods (such as highestOneBit and numberOfTrailingZeros ) are based on material from Henry S. Warren, Jr.'s Hacker's Delight , (Addison Wesley, 2002).

Since:
JDK1.0
See Also:
Serialized Form
Integer ( String s)
Constructs a newly allocated Integer object that represents the int value indicated by the String parameter.
static Integer getInteger ( String nm)
Determines the integer value of the system property with the specified name.
static Integer getInteger ( String nm, int val)
Determines the integer value of the system property with the specified name.
static Integer getInteger ( String nm, Integer val)
Returns the integer value of the system property with the specified name.
hashCode ()
Returns a hash code for this Integer .
static int highestOneBit (int i)
Returns an int value with at most a single one-bit, in the position of the highest-order ("leftmost") one-bit in the specified int value.
intValue ()
Returns the value of this Integer as an int .
longValue ()
Returns the value of this Integer as a long .
static int lowestOneBit (int i)
Returns an int value with at most a single one-bit, in the position of the lowest-order ("rightmost") one-bit in the specified int value.
static int numberOfLeadingZeros (int i)
Returns the number of zero bits preceding the highest-order ("leftmost") one-bit in the two's complement binary representation of the specified int value.
static int numberOfTrailingZeros (int i)
Returns the number of zero bits following the lowest-order ("rightmost") one-bit in the two's complement binary representation of the specified int value.
static int parseInt ( String s)
Parses the string argument as a signed decimal integer.
static int parseInt ( String s, int radix)
Parses the string argument as a signed integer in the radix specified by the second argument.
static int reverse (int i)
Returns the value obtained by reversing the order of the bits in the two's complement binary representation of the specified int value.
static int reverseBytes (int i)
Returns the value obtained by reversing the order of the bytes in the two's complement representation of the specified int value.
static int rotateLeft (int i, int distance)
Returns the value obtained by rotating the two's complement binary representation of the specified int value left by the specified number of bits.
static int rotateRight (int i, int distance)
Returns the value obtained by rotating the two's complement binary representation of the specified int value right by the specified number of bits.
short shortValue ()
Returns the value of this Integer as a short .
static int signum (int i)
Returns the signum function of the specified int value.
static String toBinaryString (int i)
Returns a string representation of the integer argument as an unsigned integer in base 2.
static String toHexString (int i)
Returns a string representation of the integer argument as an unsigned integer in base 16.
static String toOctalString (int i)
Returns a string representation of the integer argument as an unsigned integer in base 8.
String toString ()
Returns a String object representing this Integer 's value.
static String toString (int i)
Returns a String object representing the specified integer.
static String toString (int i, int radix)
Returns a string representation of the first argument in the radix specified by the second argument.
static Integer valueOf (int i)
Returns an Integer instance representing the specified int value.
static Integer valueOf ( String s)
Returns an Integer object holding the value of the specified String .
static Integer valueOf ( String s, int radix)
Returns an Integer object holding the value extracted from the specified String when parsed with the radix given by the second argument.

MIN_VALUE 

public static final int MIN_VALUE
A constant holding the minimum value an int can have, -2 31 .
See Also:
Constant Field Values

MAX_VALUE 

public static final int MAX_VALUE
A constant holding the maximum value an int can have, 2 31 -1.
See Also:
Constant Field Values 
public static final Class<Integer> TYPE
The Class instance representing the primitive type int .
Since:
JDK1.1 
public static final int SIZE
The number of bits used to represent an int value in two's complement binary form.
Since:
See Also:
Constant Field Values 
public Integer(int value)
Constructs a newly allocated Integer object that represents the specified int value.
Parameters:
value - the value to be represented by the Integer object. 
public Integer(String s)
        throws NumberFormatException
Constructs a newly allocated Integer object that represents the int value indicated by the String parameter. The string is converted to an int value in exactly the manner used by the parseInt method for radix 10.
Parameters:
s - the String to be converted to an Integer .
Throws:
NumberFormatException - if the String does not contain a parsable integer.
See Also:
parseInt(java.lang.String, int) 
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' . If radix 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) are 0123456789abcdef . If uppercase letters are desired, the String.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 2 32 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 0 s. 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, the String.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 2 32 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 leading 0 s.

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 2 32 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 leading 0 s. 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 
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 the toString(int, int) method.
Parameters:
i - an integer to be converted.
Returns:
a string representation of the argument in base 10.
int radix) throws NumberFormatException
Parses the string argument as a signed integer in the radix specified by the second argument. The characters in the string must all be digits of the specified radix (as determined by whether Character.digit(char, int) returns a nonnegative value), 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.

An exception of type NumberFormatException is thrown if any of the following situations occurs:

  • The first argument is null or is a string of length zero.
  • The radix is either smaller than Character.MIN_RADIX or larger than Character.MAX_RADIX .
  • Any character of the string is not a digit of the specified radix, except that the first character may be a minus sign '-' ( '\u002D' ) or plus sign '+' ( '\u002B' ) provided that the string is longer than length 1.
  • The value represented by the string is not a value of type int .

    Examples: parseInt("0", 10) returns 0 parseInt("473", 10) returns 473 parseInt("+42", 10) returns 42 parseInt("-0", 10) returns 0 parseInt("-FF", 16) returns -255 parseInt("1100110", 2) returns 102 parseInt("2147483647", 10) returns 2147483647 parseInt("-2147483648", 10) returns -2147483648 parseInt("2147483648", 10) throws a NumberFormatException parseInt("99", 8) throws a NumberFormatException parseInt("Kona", 10) throws a NumberFormatException parseInt("Kona", 27) returns 411787

    Parameters:
    s - the String containing the integer representation to be parsed
    radix - the radix to be used while parsing s .
    Returns:
    the integer represented by the string argument in the specified radix.
    Throws:
    NumberFormatException - if the String does not contain a parsable int . 
    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 the parseInt(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.
    throws NumberFormatException
    Returns an Integer object holding the value extracted from the specified String when parsed with the radix given by the second argument. The first argument is interpreted as representing a signed integer in the radix specified by the second argument, exactly as if the arguments were given to the parseInt(java.lang.String, int) method. The result is an Integer object that represents the integer value specified by the string.

    In other words, this method returns an Integer object equal to the value of: new Integer(Integer.parseInt(s, radix))

    Parameters:
    s - the string to be parsed.
    radix - the radix to be used in interpreting s
    Returns:
    an Integer object holding the value represented by the string argument in the specified radix.
    Throws:
    NumberFormatException - if the String does not contain a parsable int . 
    public static Integer valueOf(String s)
                       throws NumberFormatException
    Returns an Integer object holding the value of the specified String . The argument is interpreted as representing a signed decimal integer, exactly as if the argument were given to the parseInt(java.lang.String) method. The result is an Integer object that represents the integer value specified by the string.

    In other words, this method returns an Integer object equal to the value of: new Integer(Integer.parseInt(s))

    Parameters:
    s - the string to be parsed.
    Returns:
    an Integer object holding the value represented by the string argument.
    Throws:
    NumberFormatException - if the string cannot be parsed as an integer.

    valueOf 

    public static Integer valueOf(int i)
    Returns an Integer instance representing the specified int value. If a new Integer instance is not required, this method should generally be used in preference to the constructor Integer(int) , as this method is likely to yield significantly better space and time performance by caching frequently requested values. This method will always cache values in the range -128 to 127, inclusive, and may cache other values outside of this range.
    Parameters:
    i - an int value.
    Returns:
    an Integer instance representing i .
    Since:
    Overrides:
    byteValue in class Number
    Returns:
    the numeric value represented by this object after conversion to type byte .
    Overrides:
    shortValue in class Number
    Returns:
    the numeric value represented by this object after conversion to type short .
    Specified by:
    intValue in class Number
    Returns:
    the numeric value represented by this object after conversion to type int .
    Specified by:
    longValue in class Number
    Returns:
    the numeric value represented by this object after conversion to type long .
    Specified by:
    floatValue in class Number
    Returns:
    the numeric value represented by this object after conversion to type float .
    Specified by:
    doubleValue in class Number
    Returns:
    the numeric value represented by this object after conversion to type double . 
    public String toString()
    Returns a String object representing this Integer 's value. The value is converted to signed decimal representation and returned as a string, exactly as if the integer value were given as an argument to the toString(int) method.
    Overrides:
    toString in class Object
    Returns:
    a string representation of the value of this object in base 10.
    Overrides:
    hashCode in class Object
    Returns:
    a hash code value for this object, equal to the primitive int value represented by this Integer object.
    See Also:
    Object.equals(java.lang.Object) , System.identityHashCode(java.lang.Object)

    equals 

    public boolean equals(Object obj)
    Compares this object to the specified object. The result is true if and only if the argument is not null and is an Integer object that contains the same int value as this object.
    Overrides:
    equals in class Object
    Parameters:
    obj - the object to compare with.
    Returns:
    true if the objects are the same; false otherwise.
    See Also:
    Object.hashCode() , HashMap

    getInteger 

    public static Integer getInteger(String nm)
    Determines the integer value of the system property with the specified name.

    The first argument is treated as the name of a system property. System properties are accessible through the System.getProperty(java.lang.String) method. The string value of this property is then interpreted as an integer value and an Integer object representing this value is returned. Details of possible numeric formats can be found with the definition of getProperty .

    If there is no property with the specified name, if the specified name is empty or null , or if the property does not have the correct numeric format, then null is returned.

    In other words, this method returns an Integer object equal to the value of: getInteger(nm, null)

    Parameters:
    nm - property name.
    Returns:
    the Integer value of the property.
    See Also:
    System.getProperty(java.lang.String) , System.getProperty(java.lang.String, java.lang.String) 
    public static Integer getInteger(String nm,
                 int val)
    Determines the integer value of the system property with the specified name.

    The first argument is treated as the name of a system property. System properties are accessible through the System.getProperty(java.lang.String) method. The string value of this property is then interpreted as an integer value and an Integer object representing this value is returned. Details of possible numeric formats can be found with the definition of getProperty .

    The second argument is the default value. An Integer object that represents the value of the second argument is returned if there is no property of the specified name, if the property does not have the correct numeric format, or if the specified name is empty or null .

    In other words, this method returns an Integer object equal to the value of: getInteger(nm, new Integer(val)) but in practice it may be implemented in a manner such as: Integer result = getInteger(nm, null); return (result == null) ? new Integer(val) : result; to avoid the unnecessary allocation of an Integer object when the default value is not needed.

    Parameters:
    nm - property name.
    val - default value.
    Returns:
    the Integer value of the property.
    See Also:
    System.getProperty(java.lang.String) , System.getProperty(java.lang.String, java.lang.String) 
    public static Integer getInteger(String nm,
                 Integer val)
    Returns the integer value of the system property with the specified name. The first argument is treated as the name of a system property. System properties are accessible through the System.getProperty(java.lang.String) method. The string value of this property is then interpreted as an integer value, as per the Integer.decode method, and an Integer object representing this value is returned.
    • If the property value begins with the two ASCII characters 0x or the ASCII character # , not followed by a minus sign, then the rest of it is parsed as a hexadecimal integer exactly as by the method valueOf(java.lang.String, int) with radix 16.
    • If the property value begins with the ASCII character 0 followed by another character, it is parsed as an octal integer exactly as by the method valueOf(java.lang.String, int) with radix 8.
    • Otherwise, the property value is parsed as a decimal integer exactly as by the method valueOf(java.lang.String, int) with radix 10.

      The second argument is the default value. The default value is returned if there is no property of the specified name, if the property does not have the correct numeric format, or if the specified name is empty or null .

    Parameters:
    nm - property name.
    val - default value.
    Returns:
    the Integer value of the property.
    See Also:
    System.getProperty(java.lang.String) , System.getProperty(java.lang.String, java.lang.String) , decode(java.lang.String) 
    public static Integer decode(String nm)
                      throws NumberFormatException
    Decodes a String into an Integer . Accepts decimal, hexadecimal, and octal numbers given by the following grammar:
    DecodableString:
    Sign opt DecimalNumeral
    Sign opt 0x HexDigits
    Sign opt 0X HexDigits
    Sign opt # HexDigits
    Sign opt 0 OctalDigits

    Sign: DecimalNumeral , HexDigits , and OctalDigits are as defined in section 3.10.1 of The Java™ Language Specification , except that underscores are not accepted between digits.

    The sequence of characters following an optional sign and/or radix specifier (" 0x ", " 0X ", " # ", or leading zero) is parsed as by the Integer.parseInt method with the indicated radix (10, 16, or 8). This sequence of characters must represent a positive value or a NumberFormatException will be thrown. The result is negated if first character of the specified String is the minus sign. No whitespace characters are permitted in the String .

    Parameters:
    nm - the String to decode.
    Returns:
    an Integer object holding the int value represented by nm
    Throws:
    NumberFormatException - if the String does not contain a parsable integer.
    See Also:
    parseInt(java.lang.String, int)

    compareTo 

    public int compareTo(Integer anotherInteger)
    Compares two Integer objects numerically.
    Specified by:
    compareTo in interface Comparable < Integer >
    Parameters:
    anotherInteger - the Integer to be compared.
    Returns:
    the value 0 if this Integer is equal to the argument Integer ; a value less than 0 if this Integer is numerically less than the argument Integer ; and a value greater than 0 if this Integer is numerically greater than the argument Integer (signed comparison).
    Since:
    int y)
    Compares two int values numerically. The value returned is identical to what would be returned by: Integer.valueOf(x).compareTo(Integer.valueOf(y))
    Parameters:
    x - the first int to compare
    y - the second int to compare
    Returns:
    the value 0 if x == y ; a value less than 0 if x < y ; and a value greater than 0 if x > y
    Since:

    highestOneBit 

    public static int highestOneBit(int i)
    Returns an int value with at most a single one-bit, in the position of the highest-order ("leftmost") one-bit in the specified int value. Returns zero if the specified value has no one-bits in its two's complement binary representation, that is, if it is equal to zero.
    Returns:
    an int value with a single one-bit, in the position of the highest-order one-bit in the specified value, or zero if the specified value is itself equal to zero.
    Since:

    lowestOneBit 

    public static int lowestOneBit(int i)
    Returns an int value with at most a single one-bit, in the position of the lowest-order ("rightmost") one-bit in the specified int value. Returns zero if the specified value has no one-bits in its two's complement binary representation, that is, if it is equal to zero.
    Returns:
    an int value with a single one-bit, in the position of the lowest-order one-bit in the specified value, or zero if the specified value is itself equal to zero.
    Since:

    numberOfLeadingZeros 

    public static int numberOfLeadingZeros(int i)
    Returns the number of zero bits preceding the highest-order ("leftmost") one-bit in the two's complement binary representation of the specified int value. Returns 32 if the specified value has no one-bits in its two's complement representation, in other words if it is equal to zero.

    Note that this method is closely related to the logarithm base 2. For all positive int values x:

  • floor(log 2 (x)) = 31 - numberOfLeadingZeros(x)
  • ceil(log 2 (x)) = 32 - numberOfLeadingZeros(x - 1)
    Returns:
    the number of zero bits preceding the highest-order ("leftmost") one-bit in the two's complement binary representation of the specified int value, or 32 if the value is equal to zero.
    Since:

    numberOfTrailingZeros 

    public static int numberOfTrailingZeros(int i)
    Returns the number of zero bits following the lowest-order ("rightmost") one-bit in the two's complement binary representation of the specified int value. Returns 32 if the specified value has no one-bits in its two's complement representation, in other words if it is equal to zero.
    Returns:
    the number of zero bits following the lowest-order ("rightmost") one-bit in the two's complement binary representation of the specified int value, or 32 if the value is equal to zero.
    Since:

    bitCount 

    public static int bitCount(int i)
    Returns the number of one-bits in the two's complement binary representation of the specified int value. This function is sometimes referred to as the population count .
    Returns:
    the number of one-bits in the two's complement binary representation of the specified int value.
    Since: 
    public static int rotateLeft(int i,
             int distance)
    Returns the value obtained by rotating the two's complement binary representation of the specified int value left by the specified number of bits. (Bits shifted out of the left hand, or high-order, side reenter on the right, or low-order.)

    Note that left rotation with a negative distance is equivalent to right rotation: rotateLeft(val, -distance) == rotateRight(val, distance) . Note also that rotation by any multiple of 32 is a no-op, so all but the last five bits of the rotation distance can be ignored, even if the distance is negative: rotateLeft(val, distance) == rotateLeft(val, distance & 0x1F) .

    Returns:
    the value obtained by rotating the two's complement binary representation of the specified int value left by the specified number of bits.
    Since: 
    public static int rotateRight(int i,
              int distance)
    Returns the value obtained by rotating the two's complement binary representation of the specified int value right by the specified number of bits. (Bits shifted out of the right hand, or low-order, side reenter on the left, or high-order.)

    Note that right rotation with a negative distance is equivalent to left rotation: rotateRight(val, -distance) == rotateLeft(val, distance) . Note also that rotation by any multiple of 32 is a no-op, so all but the last five bits of the rotation distance can be ignored, even if the distance is negative: rotateRight(val, distance) == rotateRight(val, distance & 0x1F) .

    Returns:
    the value obtained by rotating the two's complement binary representation of the specified int value right by the specified number of bits.
    Since:

    reverse 

    public static int reverse(int i)
    Returns the value obtained by reversing the order of the bits in the two's complement binary representation of the specified int value.
    Returns:
    the value obtained by reversing order of the bits in the specified int value.
    Since:

    signum 

    public static int signum(int i)
    Returns the signum function of the specified int value. (The return value is -1 if the specified value is negative; 0 if the specified value is zero; and 1 if the specified value is positive.)
    Returns:
    the signum function of the specified int value.
    Since:

    reverseBytes 

    public static int reverseBytes(int i)
    Returns the value obtained by reversing the order of the bytes in the two's complement representation of the specified int value.
    Returns:
    the value obtained by reversing the bytes in the specified int value.
    Since:
    •  
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