Replacing unknown substring? - string

Question

public static String updatedStr(){
String [] ar= {"green","red","purple","black"};
String str="The colors are (blue), (blue), and (yellow). I prefer (orange)";
I would like a final output string of "The colors are green, red, and purple. I prefer black."

Answer 1

You can do it without using replace. Just iterate over the input String and add to a StringBuilder parts of the original String (that are not contained in parentheses) and the replacement words instead of the parts contained in parentheses.
public static String updatedStr()
{
String [] ar= {"green","red","purple","black"};
String str="The colors are (blue), (blue), and (yellow). I prefer (orange)";
StringBuilder out = new StringBuilder ();
int x = 0;
int pos = 0;
for(int i = str.indexOf('(', 0); i != -1; i = str.indexOf('(', i + 1)) {
out.append (str.substring(pos,i)); // add the part between the last ) and the next (
out.append (ar[x++]); // add replacement word
pos = str.indexOf(')', i) + 1;
}
out.append (str.substring(pos)); // add the part after the final )
return out.toString ();
}
This method returns :
The colors are green, red, and purple. I prefer black
This code makes some simplifying assumptions. For example, the number of elements in the replacements array should be at least as high as the number of words to be replaced. A more complete implementation should contain additional checks.

Answer 2

You can do this by calculating the position of where you are replacing and saving them in an array as follows:
public static String updatedStr(){
String [] ar= {"green","red","purple","black"};
String str="The colors are (blue), (blue), and (yellow). I prefer (orange)";
ArrayList<String> arr = new ArrayList<String>();
int pos [] = new int[ar.length]; // save locations here
for(int i = str.indexOf('(', 0); i != -1; i = str.indexOf('(', i + 1)) {
arr.add(str.substring(i + 1, str.indexOf(')', i)));
pos[arr.size()-1] = i; // save it!
}
// replace from right to left
for (int j=pos.length-1;j>=0;j--){
String newStr = str.substring(0, pos[j]+1) + ar[j] + str.substring(str.indexOf(')',pos[j]+1), str.length());
str = newStr;
}
return str;
}
The trick here is that I'm replacing from right to left so that the positions of where I need to replace do not move when I am replacing them.