Java.lang.string.replace() method in Java

Strings in Java are objects that are supported internally by a char array. Since arrays are immutable, and strings are also a type of exceptional array that holds characters, therefore, strings are immutable as well. 

The String class of Java comprises a lot of methods to execute various operations on strings such as compare(), concat(), equals(), split(), length(), replace(), compareTo(), substring() etc. Out of these methods, we will be focusing on the replace() method. 

String.replace() Method

This method returns a new string resulting from replacing all occurrences of old characters in the string with new characters. Here are 3 variants of replace() method. This article depicts all of them, as follows: 

1. String replace(): This method returns a new string resulting from replacing all occurrences of old characters in the string with new characters. 

Syntax:

public String replace(char oldch, char newch)

Parameters:

• oldch: the old character.
• newch: the new character.

Return Value: It returns a string derived from this string by replacing every occurrence of oldch with newch.

Example:

Java

// Java code to demonstrate the
// working of replace()

public class rep1 {
    public static void main(String args[])
    {

        // Initialising String
        String Str = new String("Welcome to geeksforgeeks");

        // Using replace to replace characters
        System.out.print("After replacing all o with T : ");
        System.out.println(Str.replace('o', 'T'));

        // Using replace to replace characters
        System.out.print("After replacing all e with D : ");
        System.out.println(Str.replace('e', 'D'));
    }
}

Output

After replacing all o with T : WelcTme tT geeksfTrgeeks
After replacing all e with D : WDlcomD to gDDksforgDDks

2. String replaceAll(): This method replaces each substring of the string that matches the given regular expression with the given replace_str. 

Syntax:

public String replaceAll(String regex, String replace_str)

Parameters:

• regex: the regular expression to which this string is to be matched.
• replace_str: the string which would replace found expression.

Return Value: This method returns the resulting String.

Example:

Java

// Java code to demonstrate the
// working of replaceAll()

public class rep2 {
    public static void main(String args[])
    {

        // Initialising String
        String Str = new String("Welcome to geeksforgeeks");

        // original string
        System.out.print("Original String : ");
        System.out.println(Str);

        // Using replaceAll to replace regex with
        // replace_str
        System.out.print(
            "After replacing regex with replace_str : ");
        System.out.println(
            Str.replaceAll("(.*)geeks(.*)", "ASTHA TYAGI"));
    }
}

Output

Original String : Welcome to geeksforgeeks
After replacing regex with replace_str : ASTHA TYAGI

3. String replaceFirst(): This method replaces the first substring of this string that matches the given regular expression with the given replace_str. 

Syntax:

public String replaceFirst(String regex, String replace_str)

Parameters:

• regex: the regular expression to which this string is to be matched.
• replace_str: the string which would replace found expression.

Return Value: This method returns a resulting String.

Example:

Java

// Java code to demonstrate the
// working of replaceFirst()

public class rep3 {
    public static void main(String args[])
    {

        // Initialising String
        String Str = new String("Welcome to geeksforgeeks");

        // original string
        System.out.print("Original String : ");
        System.out.println(Str);

        // Using replaceFirst to replace regex with
        // replace_str Replaces 1st occurrence of geeks with
        // ASTHA
        System.out.print(
            "After replacing 1st occurrence of regex with replace_str : ");
        System.out.println(
            Str.replaceFirst("geeks", "ASTHA"));
    }
}

Output

Original String : Welcome to geeksforgeeks
After replacing 1st occurrence of regex with replace_str : Welcome to ASTHAforgeeks

This article is contributed by Astha Tyagi. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.