How to replace a character at a specific index in a String in Java

February 04, 2023

In this section, we will show you how replace a character at a specific index in a String in Java.

Note: String is an immutable class in java. That means we cannot make any change in the String object. Any method which seems to modify it always returns a new string object with modification.

Following ways can be used to replace a character at a specific index in a String in Java:

By using substring () method
By using StringBuilder setCharAt() method
By using StringBuffer setCharAt() method
By using toCharArray() method

Example 1: Using substring () method

Create a new string with the character replaced.

public class Main {

    // Driver code
    public static void main(String[] args)
    {
        // Get the String
        String string = "How ate you?";

        // Get the index
        int index = 5;

        // Get the character
        char ch = 'r';

        // Print the original string
        System.out.println("Original String = " + string);

        string = string.substring(0, index) + ch
                + string.substring(index + 1);

        // Print the modified string
        System.out.println("Modified String = " + string);
    }
}

Console Output:

Original String = How ate you?
Modified String = How are you?

Example 2: Using StringBuilder setCharAt() method

The StringBuilder setCharAt() method sets a specified character at the given index. This method changes the character sequence represented by StringBuilder object as it replaces the existing char with new char.

public class Main {

    // Driver code
    public static void main(String[] args)
    {
        // Get the String
        String string = "How ate you?";

        // Get the index
        int index = 5;

        // Get the character
        char ch = 'r';

        // Print the original string
        System.out.println("Original String = " + string);

        StringBuilder result = new StringBuilder(string);
        result.setCharAt(index, ch);

        // Print the modified string
        System.out.println("Modified String = " + result);
    }
}

Console Output:

Original String = How ate you?
Modified String = How are you?

Example 3: Using StringBuffer setCharAt() method

The StringBuffer setCharAt() method sets a specified character at the given index. This method changes the character sequence represented by StringBuilder object as it replaces the existing char with new char.

public class Main {

    // Driver code
    public static void main(String[] args)
    {
        // Get the String
        String string = "How ate you?";

        // Get the index
        int index = 5;

        // Get the character
        char ch = 'r';

        // Print the original string
        System.out.println("Original String = " + string);

        StringBuffer result = new StringBuffer(string);
        result.setCharAt(index, ch);

        // Print the modified string
        System.out.println("Modified String = " + result);
    }
}

Console Output:

Original String = How ate you?
Modified String = How are you?

Example 4: Using toCharArray() method

The given string is converted to a character array using toCharArray() method and then replace the character at the given index in the character array. Finally, convert the character array back into a string using String.valueOf(char[]) method.

public class Main {

    // Driver code
    public static void main(String[] args)
    {
        // Get the String
        String string = "How ate you?";

        // Get the index
        int index = 5;

        // Get the character
        char ch = 'r';

        // Print the original string
        System.out.println("Original String = " + string);

        // convert the given string to a character array
        char[] chars = string.toCharArray();

        // replace character at the specified position in a char array
        chars[index] = ch;

        // convert the character array back into a string
        string = String.valueOf(chars);

        // Print the modified string
        System.out.println("Modified String = " + string);
    }
}

Console Output:

Original String = How ate you?
Modified String = How are you?

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