question: public static Element firstChildElement ( Element element , Set < String > childElementNames ) { if ( element == null ) return null ; Node node = element . getFirstChild ( ) ; if ( node != null ) { do { if ( node . getNodeType ( ) == Node . ELEMENT_NODE && childElementNames . contains ( node . getNodeName ( ) ) ) { Element childElement = ( Element ) node ; return childElement ; } } while ( ( node = node . getNextSibling ( ) ) != null ) ; } return null ; }
target:  Return the first child Element returns the first element. 