Why a String substring (int, int) method declaration without throwsIndexOutOfBoundsException

The String substring (int, int) method throws IndexOutOfBoundsException exception ,
But why did not the declaration of the method throws IndexOutOfBoundsException it ?

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this is a runtime exception , which is able to avoid through the code with no throws
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because IndexOutOfBoundsException is a subclass of RuntimeException , belonging to a runtime exception , no declaration.
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because it is java.lang.RuntimeException exception.

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original, learn . . . Results posted .
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, the child is java.lang.RuntimeException exception thrown without declaring