Replace the last occurrence of a string in another string [duplicate]

Question

Let's say I have a string

string myWord="AAAAA";

I want to replace "AA" with "BB", but only the last occurrence, like so:

"AAABB"

Neither string.replace() nor string.replaceFirst() would do the job. Is there a string.replaceLast()? And, If not, will there ever be one or is there an alternative also working with regexes?

Answer 1

Find the index of the last occurrence of the substring.

String myWord = "AAAAAasdas";
String toReplace = "AA";
String replacement = "BBB";

int start = myWord.lastIndexOf(toReplace);

Create a StringBuilder (you can just concatenate Strings if you wanted to).

StringBuilder builder = new StringBuilder();

Append the part before the last occurrence.

builder.append(myWord.substring(0, start));

Append the String you want to use as a replacement.

builder.append(replacement);

Append the part after the last occurrence from the original `String.

builder.append(myWord.substring(start + toReplace.length()));

And you're done.

System.out.println(builder);

Answer 2

You can do this:

myWord = myWord.replaceAll("AA$","BB");

$ means at the last.

Answer 3

Just get the last index and do an in place replacement of the expression with what you want to replace.

myWord is the original word sayAABDCAADEF. sourceWord is what you want to replace, say AA targetWord is what you want to replace it with say BB.

StringBuilder strb=new StringBuilder(myWord);    
int index=strb.lastIndexOf(sourceWord);    
strb.replace(index,sourceWord.length()+index,targetWord);    
return strb.toString();

This is useful when you want to just replace strings with Strings.A better way to do it is to use Pattern matcher and find the last matching index. Take as substring from that index, use the replace function there and then add it back to the original String. This will help you to replace regular expressions as well