How to represent infinity in Java?

Introduction

"Infinity (symbolically represented with ∞) comes from the Latin infinitas or "unboundedness." It refers to several distinct concepts – usually linked to the idea of "without end" – which arise in philosophy, mathematics, and theology.

In mathematics, "infinity" is often used in contexts where it is treated as if it were a number (i.e., it counts or measures things: "an infinite number of terms")" http://en.wikipedia.org/wiki/Infinity

How is infinity represented in Java?

In Java, the wrapper classes (Double and Float) that wrap the value of the primary types double and float each in an object contain static constants holding the value of infinity of its respective type.

There are two of types infinities:

• Negative Infinity (In mathematics, symbolically represented by -∞)
• Positive Infinity (In mathematics, symbolically represented by ∞)

Number Classes

Class Double and Float extend the class Number- "The abstract class Number is the superclass of classes BigDecimal, BigInteger, Byte, Double, Float, Integer, Long, and Short." see Java Docs

Double - Negative and Positive Infinities 

• Double.NEGATIVE_INFINITY

A constant holding the negative infinity of type double.

• Double.POSITIVE_INFINITY

A constant holding the positive infinity of type double.

Float - Negative and Positive Infinities

• Float.NEGATIVE_INFINITY

A constant holding the negative infinity of type float .

• Float.POSITIVE_INFINITY

A constant holding the positive infinity of type float.

Examples

Consider some simple examples below

Using Negative Infinity:

In this example, the input is a number and and the number's validity should be checked by the given condition: 

Condition for Validity: (-∞ <= x <= 20)

public boolean checkNumber(double number)
{
    if( number >= Double.NEGATIVE_INFINITY && number <= 20 )
    {
       return true;
    }
}

Using Positive Infinity:

In this example, the length of a String should only belong to only the specified range. The given range/restriction for the String is (1 <= x <= ∞)

public boolean checkLength(String value)
{
    int length = value.length();
    if( length >= 1 && length <= Double.POSITIVE_INFINITY )
    {
        return true;
    }
}