Question

which of the following is an efficient way to reverse words in a string ?

public String Reverse(StringTokenizer st){
    String[] words = new String[st.countTokens()];
    int i = 0;
    while(st.hasMoreTokens()){
       words[i] = st.nextToken();i++}

    for(int j = words.length-1;j--)
       output = words[j]+" ";}

OR

public String Reverse(StringTokenizer st, String output){        
    if(!st.hasMoreTokens()) return output;        
        output = st.nextToken()+" "+output;
        return Reverse(st, output);}       

public String ReverseMain(StringTokenizer st){       
    return Reverse(st, "");}

while the first way seems more readable and straight forward, there are two loops in it. In the 2nd method, I’ve tried doing it in tail-recursive way. But I am not sure whether java does optimize tail-recursive code.

Answer 1

you could do this in just one loop

public String Reverse(StringTokenizer st){
    int length = st.countTokens();
    String[] words = new String[length];
    int i = length - 1;
    while(i >= 0){
      words[i] = st.nextToken();i--}
}