Java String replace(), replaceAll() and replaceFirst() method

The String Class Java has three types of Replace methods:

1. replace()
2. replaceAll()
3. replaceFirst()

With the help of replace() function in Java, you can replace characters in your string. Lets study each Java string API functions in details:

Syntax:

public Str replace(char oldC, char newC)

Parameters:

oldCh − old character

newCh − new character

Return Value

The Java replace() function returns a string by replacing oldCh with newCh.

Example of replace() in Java:

Let’s understand replace() in Java function with an example:

public class Guru99Ex1 {
    public static void main(String args[]) {
        String S1 = new String("the quick fox jumped");
        System.out.println("Original String is ': " + S1);
        System.out.println("String after replacing 'fox' with 'dog': " + S1.replace("fox", "dog"));
        System.out.println("String after replacing all 't' with 'a': " + S1.replace('t', 'a'));

    }
}

Expected Output:

Original String is ': the quick fox jumped
String after replacing 'fox' with 'dog': the quick dog jumped
String after replacing all 't' with 'a': ahe quick fox jumped

Signature:

public Str replaceAll(String regex, String replacement)

Parameters:

regx: regular expression

replacement: replacement sequence of characters

Example:

public class Guru99Ex2 {
    public static void main(String args[]) {
        String str = "Guru99 is a site providing free tutorials";
        //remove white spaces
        String str2 = str.replaceAll("\\s", "");
        System.out.println(str2);
    }
}

Expected Output:

Guru99isasiteprovidingfreetutorials

Syntax

public Str replaceFirst(String rgex, String replacement)

Parameters

rgex − the regular expression to which given string need to matched.

replacement − the string that replaces regular expression.

Return Value

This method returns resulting String as an output.

Example of replaceFirst() in Java:

public class Guru99Ex2 {
    public static void main(String args[]) {
        String str = "This website providing free tutorials";
        //Only Replace first 's' with '9' 
        String str1 = str.replaceFirst("s", "9");
        System.out.println(str1);
    }
}

Expected Output:

Thi9 website providing free tutorials

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