private static ArrayIndexOutOfBoundsException error(final int index) {
		return new ArrayIndexOutOfBoundsException(format(
			"Child index is out of bounds: %s", index
		));
	}
Sets the user object for this node.

@param value the node {@code value}
jenetics.incubator/src/main/java/io/jenetics/incubator/util/BinaryTree.java