public String reverseWordsInASentence(String sentence){

String reversedSentence;

if(sentence != null){

List<String> sentenceList = sentence.split(' ');

System.debug('Convert sentence to a list: ' + sentenceList);

//reverse list order

List<String> reverseList = new List<String>();

for(Integer i = sentenceList.size()-1; i >= 0; i--){

reverseList.add(sentenceList.get(i));

System.debug('i = ' + i + ' reverseList: ' + reverseList );

}

reversedSentence = String.join(reverseList,' ');

System.debug('reversed sentence: ' + reversedSentence);

}

return reversedSentence;

}