How to check String contains only white space characters in Apex ?

<div aria-level="3" role="heading">Apex String Methods to Determine Character Types
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1. isAlpha() : This string method will return true, if the string contain only characters.
2. isAlphaSpace() : This string method will return true, if the string contain alphabet and white spaces.
3. isAlphanumeric() : This string method will return true, if the string contain alphabet, numbers.

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