Replacing all occurrences of a substring in a string without using regex

Question

Problem Statement:

Given two strings, base and remove, return a version of the base string where all instances of the remove string have been removed (not case sensitive). You may assume that the remove string is length 1 or more. Remove only non-overlapping instances, so with "xxx" removing "xx" leaves "x".

---

withoutString("Hello there", "llo") → "He there"

withoutString("Hello there", "e") → "Hllo thr"

withoutString("Hello there", "x") → "Hello there"

Please feel free to review the code below:

public String withoutString(String base, String remove) {
 final int rLen = remove.length();
 final int bLen = base.length();
 String op = "";
 for(int i = 0; i < bLen;)
 {
 if( !(i + rLen > bLen) && base.substring(i, i + rLen).equalsIgnoreCase(remove) )
 {
 i += rLen;
 continue;
 }
 op += base.substring(i, i + 1);
 i++;
 }
 return op; 
}

Answer 1

Using a StringBuilder should always be your preferred choice when doing String manipulation. It does not always make sense, but almost always.

Additionally, indexOf takes a 'from' location, and it makes the whole thing easier.... Convert both inputs to lower-case, then do the matching using the lower-case versions, but the substrings using the unknown-case.

The complicated assign-in-where-condition logic makes the loop conditions easier, but you do need to understand what this does:

while ((find = lcbase.indexOf(lcremove, previous)) >= 0) {

it searches for thelower-case remove from the previous position, saves the value to find, and checks that the result is 'positive'.... all in the condition of a while loop.

The full code is:

public static String withoutString(String base, String remove) {
 final String lcbase = base.toLowerCase();
 final String lcremove = remove.toLowerCase();
 int find = 0;
 int previous = 0;
 StringBuilder result = new StringBuilder(base.length());
 while ((find = lcbase.indexOf(lcremove, previous)) >= 0) {
 result.append(base.substring(previous, find));
 previous = find + remove.length();
 }
 result.append(base.substring(previous));
 return result.toString();
}

See this running inideone