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Java Language Reference

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Float

Name

Float

Synopsis

Class Name:

java.lang.Float

Superclass:

java.lang.Number

Immediate Subclasses:

None

Interfaces Implemented:

None

Availability:

JDK 1.0 or later

Description

The Float class provides an object wrapper for a float value. This is useful when you need to treat a float value as an object. For example, there are a number of utility methods that take a reference to an Object as one of their arguments. You cannot specify a float value for one of these arguments, but you can provide a reference to a Float object that encapsulates the float value. Furthermore, as of JDK 1.1, the Float class is necessary to support the Reflection API and class literals.

In Java, float values are represented using the IEEE 754 format. The Float class provides constants for the three special values that are mandated by this format: POSITIVE_INFINITY, NEGATIVE_INFINITY, and NaN (not-a-number).

The Float class also provides some utility methods, such as methods for determining whether a floatx value is an infinity value or NaN, for converting float values to other primitive types, and for converting a float to a String and vice versa.

Class Summary

public final class java.lang.Float extends java.lang.Number {
    // Constants
    public static final float MIN_VALUE;
    public static final float MAX_VALUE;
    public static final float NaN;
    public static final float NEGATIVE_INFINITY;
    public static final float POSITIVE_INFINITY;
    public final static Class TYPE;                    // New in 1.1
    // Constructors
    public Float(double value);
    public Float(float value);
    public Float(String s);
    // Class Methods
    public static native int floatToIntBits(float value);
    public static native float intBitsToFloat(int bits);
    public static boolean isInfinite(float v);
    public static boolean isNaN(float v);
    public static String toString(float f);
    public static Float valueOf(String s);
    // Instance Methods
    public byte byteValue();                           // New in 1.1
    public double doubleValue();
    public boolean equals(Object obj);
    public float floatValue();
    public int hashCode();
    public int intValue();
    public boolean isInfinite();
    public boolean isNaN();
    public long longValue();
    public short shortValue();                         // New in 1.1
    public String toString();
}

Constants

MAX_VALUE

public static final float MAX_VALUE = 3.40282346638528860e+38f

Description

The largest value that can be represented by a float.

MIN_VALUE

public static final float MIN_VALUE = 1.40129846432481707e-45f

Description

The smallest value that can be represented by a float.

NaN

public static final float NaN = 0.0f / 0.0f

Description

This variable represents the value NaN, a special value produced by float operations such as division of zero by zero. When NaN is one of the operands, most arithmetic operations return NaN as the result. Most comparison operators (<, <=, ==, >=, >) return false when one of their arguments is NaN. The exception is !=, which returns true when one of its arguments is NaN.

NEGATIVE_INFINITY

public static final float NEGATIVE_INFINITY = -1.0f / 0.0f

Description

This variable represents the value negative infinity, which is produced when a float operation underflows or a negative float value is divided by zero. Negative infinity is by definition less than any other float value.

POSITIVE_INFINITY

public static final float POSITIVE_INFINITY = 1.0f / 0.0f

Description

This variable represents the value positive infinity, which is produced when a float operation overflows or a positive float value is divided by zero. Positive infinity is by definition greater than any other float value.

TYPE

public static final Class TYPE

Availability

New as of JDK 1.1

Description

The Class object that represents the type float. It is always true that Float.TYPE == float.class.

Constructors

Float

public Float(double value)

Parameters

value

The double value to be encapsulated by this object.

Description

Creates a Float object with the specified double value. The value is rounded to float precision.

public Float(float value)

Parameters

value

The float value to be encapsulated by this object.

Description

Creates a Float object with the specified float value.

public Float(String s) throws NumberFormatException

Parameters

s

The string to be made into a Float object.

Throws

NumberFormatException

If the sequence of characters in the given String does not form a valid float literal.

Description

Constructs a Float object with the value specified by the given string. The string must contain a sequence of characters that forms a legal float literal.

Class Methods

floatToIntBits

public static native int floatToIntBits(float value)

Parameters

value

The float value to be converted.

Returns

The int value that contains the same sequence of bits as the representation of the given float value.

Description

This method returns the int value that contains the same sequence of bits as the representation of the given float value. The meaning of the bits in the result is defined by the IEEE 754 floating-point format: bit 31 is the sign bit, bits 30-23 are the exponent, and bits 22-0 are the mantissa. An argument of POSITIVE_INFINITY produces the result 0x7f800000, an argument of NEGATIVE_INFINITY produces the result 0xff800000, and an argument of NaN produces the result 0x7fc00000.

The value returned by this method can be converted back to the original float value by the intBitsToFloat() method.

intBitsToFloat

public static native float intBitsToFloat(int bits)

Parameters

bits

The int value to be converted.

Returns

The float value whose representation is the same as the bits in the given int value.

Description

This method returns the float value whose representation is the same as the bits in the given int value. The meaning of the bits in the int value is defined by the IEEE 754 floating-point format: bit 31 is the sign bit, bits 30-23 are the exponent, and bits 22-0 are the mantissa. The argument 0x7f800000 produces the result POSITIVE_INFINITY, and the argument 0xff800000 produces the result NEGATIVE_INFINITY. Arguments in the ranges 0x7f800001 through 0x7f8fffff and 0xff800001 through 0xff8fffffL all produce the result NaN.

Except for NaN values not normally used by Java, this method is the inverse of the floatToIntBits() method.

isInfinite

public static boolean isInfinite(float v)

Parameters

v

The float value to be tested.

Returns

true if the specified value is equal to POSITIVE_INFINITY or NEGATIVE_INFINITY; otherwise false.

Description

This method determines whether or not the specified value is an infinity value.

isNaN

public static boolean isNaN(float v)

Parameters

v

The float value to be tested.

Returns

true if the specified value is equal to NaN; otherwise false.

Description

This method determines whether or not the specified value is NaN.

toString

public static String toString(float f)

Parameters

f

The float value to be converted.

Returns

A string representation of the given value.

Description

This method returns a String object that contains a representation of the given float value.

The values NaN, NEGATIVE_INFINITY, POSITIVE_INFINITY, -0.0, and +0.0 are represented by the strings "NaN", "--Infinity", "Infinity", "--0.0", and "0.0", respectively.

For other values, the exact string representation depends on the value being converted. If the absolute value of f is greater than or equal to 10^-3 or less than or equal to 10^7, it is converted to a string with an optional minus sign (if the value is negative) followed by up to eight digits before the decimal point, a decimal point, and the necessary number of digits after the decimal point (but no trailing zero if there is more than one significant digit). There is always a minimum of one digit after the decimal point.

Otherwise, the value is converted to a string with an optional minus sign (if the value is negative), followed by a single digit, a decimal point, the necessary number of digits after the decimal point (but no trailing zero if there is more than one significant digit), and the letter E followed by a plus or a minus sign and a base 10 exponent of at least one digit. Again, there is always a minimum of one digit after the decimal point.

Note that the definition of this method has changed as of JDK 1.1. Prior to that release, the method provided a string representation that was equivalent to the %g format of the printf function in C.

valueOf

 public static Float valueOf(String s) throws NumberFormatException 

Parameters

s

The string to be made into a Float object.

Returns

The Float object constructed from the string.

Throws

NumberFormatException

If the sequence of characters in the given String does not form a valid float literal.

Description

Constructs a Float object with the value specified by the given string. The string must contain a sequence of characters that forms a legal float literal. This method ignores leading and trailing whitespace in the string.

Instance Methods

byteValue

public byte byteValue()

Availability

New as of JDK 1.1

Returns

The value of this object as a byte.

Overrides

Number.byteValue()

Description

This method returns the truncated value of this object as a byte. More specifically, if the value of the object is NaN, the method returns 0. If the value is POSITIVE_INFINITY, or any other value that is too large to be represented by an byte, the method returns Byte.MAX_VALUE. If the value is NEGATIVE_INFINITY, or any other value that is too small to be represented by an byte, the method returns Byte.MIN_VALUE. Otherwise, the value is rounded toward zero and returned.

doubleValue

public double doubleValue()

Returns

The value of this object as a double.

Overrides

Number.doubleValue()

Description

This method returns the value of this object as a double.

equals

public boolean equals(Object obj)

Parameters

obj

The object to be compared with this object.

Returns

true if the objects are equal; false if they are not.

Overrides

Object.equals()

Description

This method returns true if obj is an instance of Float and it contains the same value as the object this method is associated with. More specifically, the method returns true if the floatToIntBits() method returns the same result for the values of both objects.

This method produces a different result than the == operator when both values are NaN. In this case, the == operator produces false, while this method returns true. By the same token, the method also produces a different result when the two values are +0.0 and -0.0. In this case, the == operator produces true, while this method returns false.

floatValue

public float floatValue()

Returns

The value of this object as a float.

Overrides

Number.floatValue()

Description

This method returns the value of this object as a float.

hashCode

public int hashCode()

Returns

A hashcode based on the float value of the object.

Overrides

Object.hashCode()

Description

This method returns a hashcode computed from the value of this object. More specifically, if f is the value of the object, this method returns Float.floatToIntBits(f).

intValue

public int intValue()

Returns

The value of this object as an int.

Overrides

Number.intValue()

Description

This method returns the truncated value of this object as an int. More specifically, if the value of the object is NaN, the method returns 0. If the value is POSITIVE_INFINITY, or any other value that is too large to be represented by an int, the method returns Integer.MAX_VALUE. If the value is NEGATIVE_INFINITY, or any other value that is too small to be represented by an int, the method returns Integer.MIN_VALUE. Otherwise, the value is rounded toward zero and returned.

isInfinite

public boolean isInfinite(float v)

Returns

true if the value of this object is equal to POSITIVE_INFINITY or NEGATIVE_INFINITY; otherwise false.

Description

This method determines whether or not the value of this object is an infinity value.

isNaN

public boolean isNaN()

Returns

true if the value of this object is equal to NaN; otherwise false.

Description

This method determines whether or not the value of this object is NaN.

longValue

public long longValue()

Returns

The value of this object as a long.

Overrides

Number.longValue()

Description

This method returns the truncated value of this object as a long. More specifically, if the value of the object is NaN, the method returns 0. If the value is POSITIVE_INFINITY, or any other value that is too large to be represented by a long, the method returns Long.MAX_VALUE. If the value is NEGATIVE_INFINITY, or any other value that is too small to be represented by a long, the method returns Long.MIN_VALUE. Otherwise, the value is rounded toward zero and returned.

shortValue

public short shortValue()

Availability

New as of JDK 1.1

Returns

The value of this object as a short.

Overrides

Number.shortValue()

Description

This method returns the truncated value of this object as a short. More specifically, if the value of the object is NaN, the method returns 0. If the value is POSITIVE_INFINITY, or any other value that is too large to be represented by an short, the method returns Short.MAX_VALUE. If the value is NEGATIVE_INFINITY, or any other value that is too small to be represented by an short, the method returns Short.MIN_VALUE. Otherwise, the value is rounded toward zero and returned.

toString

public String toString()

Returns

A string representation of the value of this object.

Overrides

Object.toString()

Description

This method returns a String object that contains a representation of the value of this object.

The values NaN, NEGATIVE_INFINITY, POSITIVE_INFINITY, -0.0, and +0.0 are represented by the strings "NaN", "--Infinity", "Infinity", "--0.0", and "0.0", respectively.

For other values, the exact string representation depends on the value being converted. If the absolute value of this object is greater than or equal to 10^-3 or less than or equal to 10^7, it is converted to a string with an optional minus sign (if the value is negative) followed by up to eight digits before the decimal point, a decimal point, and the necessary number of digits after the decimal point (but no trailing zero if there is more than one significant digit). There is always a minimum of one digit after the decimal point.

Otherwise, the value is converted to a string with an optional minus sign (if the value is negative), followed by a single digit, a decimal point, the necessary number of digits after the decimal point (but no trailing zero if there is more than one significant digit), and the letter E followed by a plus or a minus sign and a base 10 exponent of at least one digit. Again, there is always a minimum of one digit after the decimal point.

Note that the definition of this method has changed as of JDK 1.1. Prior to that release, the method provided a string representation that was equivalent to the %g format of the printf function in C.

Inherited Methods

Method

Inherited From

Method

Inherited From

clone()

Object

finalize()

Object

getClass()

Object

notify()

Object

notifyAll()

Object

wait()

Object

wait(long)

Object

wait(long, int)

Object

See Also

Class; Double; Exceptions; Floating-point literals; Floating-point types; Number; String


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