java怎么表示正无穷大_java中怎样表示一个无穷大? 无穷小?
Java中提供了三个特殊的浮点数值：正无穷大、负无穷大、非数，用于表示溢出和出错。
正无穷大：用一个正数除以0将得到一个正无穷大，通过Double或Float的POSITIVE_INFINITY表示。
负无穷大：用一个负数除以0将得到一个负无穷大，通过Double或Float的NEGATIVE_INFINITY表示。
非数：0.0除以0.0或对一个负数开放将得到一个非数，通过Double或Float的NaN表示。
可以点开jdk源码，看看java都是如何表示的：
/**
* The {@code Double} class wraps a value of the primitive type
* {@code double} in an object. An object of type
* {@code Double} contains a single field whose type is
* {@code double}.
*
*
In addition, this class provides several methods for converting a
* {@code double} to a {@code String} and a
* {@code String} to a {@code double}, as well as other
* constants and methods useful when dealing with a
* {@code double}.
*
* @author Lee Boynton
* @author Arthur van Hoff
* @author Joseph D. Darcy
* @since JDK1.0
*/
public final class Double extends Number implements Comparable {
/**
* A constant holding the positive infinity of type
* {@code double}. It is equal to the value returned by
* {@code Double.longBitsToDouble(0x7ff0000000000000L)}.
*/
public static final double POSITIVE_INFINITY = 1.0 / 0.0;
/**
* A constant holding the negative infinity of type
* {@code double}. It is equal to the value returned by
* {@code Double.longBitsToDouble(0xfff0000000000000L)}.
*/
public static final double NEGATIVE_INFINITY = -1.0 / 0.0;
/**
* A constant holding a Not-a-Number (NaN) value of type
* {@code double}. It is equivalent to the value returned by
* {@code Double.longBitsToDouble(0x7ff8000000000000L)}.
*/
public static final double NaN = 0.0d / 0.0;
...
}
(实际上在字节码里正无穷和负无穷还有NaN都有一个特定的值用来表示
0x7f800000表示正无穷
0xff800000表示负无穷
在0x7f800001~0x7fffffff 和 0xff80001~0xffffffff两个的范围内的值表示NaN.
)
所有的正无穷大的数值都是相等的，所有的负无穷大的数值都是相等；而NaN不与任何数值相等，甚至和NaN都不等。
举例
public class javaLesson5
{
public static void main(String[] args)
{
float af = 5.2325556f;
//下面将看到af的值已经发生改变,显示结果为5.2325554.
System.out.println(af);
double a = 0.0;
double c = Double.NEGATIVE_INFINITY;
float d = Float.NEGATIVE_INFINITY;
//将看到float和double的负无穷大是相等的。显示结果为：true。
System.out.println(c == d);
//0.0除以0.0将出现非数。显示结果为：NaN。
System.out.println(a / a);
//两个非数之间是不相等的。显示结果为：false。
System.out.println(a == Float.NaN);
//所有正无穷大都是相等的。显示结果为：true。
System.out.println(6.0 / 0 == 555.0/0);
//负数除以0.0将得到负无穷大。显示结果为：-Infinity
System.out.println(-8 / a);
//下面代码将抛出除以0的异常。
//System.out.pintln(0 / 0);
}
}
部分内容转自(http://blog.csdn.net/ml863606/article/details/50853555)