Search and Replace a Substring in Java Example

Welcome back to Java Code Online. Very often in programming we need to search and replace particular instances of substring in a String. There are multiple ways of doing it, and the Java String class provides many methods and ways to doing the same. I am presenting some of the most common ways to achieve the same.

Using substring() method

The substring() method could be used to search and replace a substring in the main String. The below example searches and replaces the first instance of a substring in the original String.

    package JavaTest1;

    //This class search and replace the first
    //instance of a String in the main String.
    public class SearchReplaceSubString {

        /**
         * @param args
         */
        public static void main(String[] args) {

            String str = "This is a search and replace of substring example";

            System.out.println("The original String is: " + str);

            // We want to look for the String "search" and replace it with "find"
            String searchQuery = "search";
            String replaceWord = "find";
            int startIndexVal = 0;
            int endIndexVal = 0;

            // look for the starting index of searchQuery
            startIndexVal = str.indexOf(searchQuery);

            // evaluate the ending Index of searchQuery
            endIndexVal = startIndexVal + searchQuery.length();

            // Form the string again using the substring() method
            str = str.substring(0, startIndexVal) + replaceWord
                    + str.substring(endIndexVal);

            System.out.println("The modified String is: " + str);

        }

    }

When the above code is executed the output is:-

    The original String is: This is a search and replace of substring example
    The modified String is: This is a find and replace of substring example

Using replace() method

The String Class provides a very effective way to replace all the occurrences of a substring in the main string
It uses the replace() method of the String class. The example below looks for a substring and replaces all the occurrences of that substring with a new substring.

    package JavaTest1;

    //This class search and replace all the
    //instances of a substring in the main String.
    public class SearchReplaceSubString {

        /**
         * @param args
         */
        public static void main(String[] args) {

            String str = "Using Replace method for the searching and searching and replacing of a substring in a String";

            System.out.println("The original String is: " + str);

            // We want to look for the String "search" and replace it with "find"
            String searchWord = "search";
            String replaceWord = "find";

            // Replace all the occurrences of the searchWord with the replaceWord
            str = str.replace(searchWord, replaceWord);

            System.out.println("The modified String is: " + str);
        }
    }

When the example code is run, then the output is:-

     The original String is: Using Replace method for the searching and searching and replacing of a substring in a String
    The modified String is: Using Replace method for the finding and finding and replacing of a substring in a String

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