In-place replace multiple occurrences of a pattern

// Java equivalent
// Java program to in-place replace multiple
// occurrences of a pattern by character ‘X’
public class ReplaceOccurrences 
{ 

  // returns true if pattern is prefix of str 
  public static boolean compare(String str, String pattern) 
  { 
    for (int i = 0; i<pattern.length(); i++) 
      if (str.charAt(i) != pattern.charAt(i)) 
        return false; 
    return true; 
  } 

  // Function to in-place replace multiple 
  // occurrences of a pattern by character ‘X’ 
  public static String replacePattern(String str, String pattern) 
  { 
    // If pattern is null or empty string, 
    // nothing needs to be done 
    if (pattern == "") 
      return str; 

    int len = pattern.length(); 
    if (len == 0) 
      return str; 

    int i = 0, j = 0; 
    int count; 

    // for each character 
    while (j<str.length()) 
    { 
      count = 0; 

      // compare str[j..j+len] with pattern 
      if (j + len <= str.length() && compare(str.substring(j,j+len), pattern)) 
      { 
        // increment j by length of pattern 
        j = j + len; 
        count++; 
      } 

      // If single or multiple occurrences of pattern 
      // is found, replace it by character 'X' 
      if (count > 0) 
      { 
        String firstPart = str.substring(0,i); 
        String lastPart = str.substring(i+1); 
        str = firstPart + 'X' + lastPart; 
        i++; 
      } 

      // copy character at current position j 
      // to position i and increment i and j 
      if (j<str.length()) 
      { 
        String firstPart = str.substring(0,i); 
        String lastPart = str.substring(i+1); 
        str = firstPart + str.charAt(j) + lastPart; 
        i++; j++; 
      } 
    } 

    // add a null character to terminate string 
    String firstPart = str.substring(0,i); 
    str = firstPart; 
    return str; 
  } 

  // Driver code 
  public static void main(String[] args) 
  { 
    String str = "GeeksforGeeks"; 
    String pattern = "Geeks"; 

    str = replacePattern(str, pattern); 
    System.out.println(str); 
  } 
}

/*package whatever //do not write package name here */

import java.io.*;

public class GFG {
    // Function to in-place replace multiple occurrences of a pattern by character ‘X’
    static void replacePattern(StringBuilder str, String pattern) {
        // run this loop until string str is empty
        while (str.length() > 0) {
            // searching the first index in string str where the first occurrence of string pattern occurs
            int index = str.indexOf(pattern);
            
            // checking if pattern is found in string str
            if (index >= 0) {
                // erasing the full pattern string from that index position in string str
                str.delete(index, index + pattern.length());
                
                // inserting 'X' at that index position
                str.insert(index, "X");
            } else {
                // if pattern is not found in string str, exit loop
                break;
            }
        }

        // this loop removes consecutive 'X' in string s
        // Example: GeeksGeeksforGeeks was changed to 'XXforX'
        // running this loop will change it to 'XforX'
        for (int i = 0; i < str.length() - 1; i++) {
            if (str.charAt(i) == 'X' && str.charAt(i + 1) == 'X') {
                // removing 'X' at position i in string str
                str.deleteCharAt(i);
                i--; // i-- because one character was deleted so repositioning i
            }
        }

        System.out.println(str);
    }

    public static void main(String[] args) {
        StringBuilder str = new StringBuilder("GeeksforGeeks");
        String pattern = "Geeks";

        replacePattern(str, pattern);
    }
}