The replace() method has two forms. The first replaces all occurrences of one character in the invoking string with another character. It has the following general form:

String replace(char original, char replacement)

Here, original specifies the character to be replaced by the character specified by replacement. The resulting string is returned. For example,

String s = "Hello".replace('l', 'w');

puts the string "Hewwo" into s.

The second form of replace() replaces one character sequence with another. It has this general form:

String replace(CharSequence original, CharSequence replacement)

Java String replace() Method Example

This is a complete example to demonstrate the usage of replace() methods.

public class ReplaceExample {
    public static void main(String[] args) {
        String str = "javaguides";
        String subStr = str.replace('a', 'b');
        System.out.println("replace char 'a' with char 'b' from given string : " + subStr);
        subStr = str.replace("guides", "tutorials");
        System.out.println("replace guides with tutorials from given string : " + subStr);
        subStr = str.replaceAll("[a-z]", "java");
        System.out.println(subStr);
        subStr = str.replaceFirst("[a-z]", "java");
        System.out.println(subStr);
    }
}

Output:

replace char 'a' with char 'b' from given string: jbvbguides replace guides with tutorials from given string: javatutorials javajavajavajavajavajavajavajavajavajava javaavaguides 

Reference

https://www.javaguides.net/2018/08/java-string-class-api-guide.html