Java String has three types of Replace method

  1. replace
  2. replaceAll
  3. replaceFirst.

With the help of these you can replace characters in your string. Lets study each in details:

Java String replace() Method

Java String replace() method replaces every occurrence of a given character with a new character and returns a new string. This method allows the replacement of a sequence of character values.

Syntax:

public Str replace(char oldC, char newC)

Parameters:

oldCh − old character.

newCh − new character.

Return Value

This function returns a string by replacing oldCh with newCh.

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'));

    }
}

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

Java String Replaceall()

Java String replaceAll() method finds all occurrences of sequence of characters matching a regular expression and replaces them with the replacement string. At the end of call, a new string is returned by the function.

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);
    }
}

Output:

Guru99isasiteprovidingfreetutorials

Java String Replaceall()

Java String replaceFirst() method replaces ONLY the first substring which matches a given regular expression. Matching of the string starts from the beginning of a string (left to right). At the end of call, a new string is returned by the function.

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:

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);
    }
}

Output:

Thi9 website providing free tutorials

 

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