Java - replace first character in string

In this article, we would like to show you how to replace the first character in string in Java.

Quick solution:

String text = "ABC";
String replacement = "x";
String result = replacement + text.substring(1);

System.out.println(result);  // xBC

or:

String text = "ABC";
String replacement = "x";
String result = replacement.concat(text.substring(1));

System.out.println(result);  // xBC

or:

String text = "ABC";
String replacement = "x";
String result = text.replaceAll("^.", replacement);

System.out.println(result);  // xBC

1. Practical example using String substring()

1.1 With + operator

In this example, we remove last character from the original string and add the replacement at the beginning.

public class Example {

    public static void main(String[] args) {
        String text = "ABC";
        String replacement = "x";
        String result = replacement + text.substring(1);

        System.out.println(result);  // xBC
    }
}

1.2 With concat() method

This approach is equivalent to the above one. Instead of + operator we concatenate the strings using concat() method.

public class Example {

    public static void main(String[] args) {
        String text = "ABC";
        String replacement = "x";
        String result = replacement.concat(text.substring(1));

        System.out.println(result);  // xBC
    }
}

2. Practical example using String replaceAll() with regex pattern

In this example, we use string replaceAll() with "^." regex to replace the first character in the text string.

Regex explanation:

• ^ - matches the beginning of the string,
• . - matches any character except linebreaks.

public class Example {

    public static void main(String[] args) {
        String text = "ABC";
        String replacement = "x";
        String result = text.replaceAll("^.", replacement);

        System.out.println(result);  // xBC
    }
}

Note:

Regular expressions are slower than substring() method.