Java String replaceAll() Method

String replaceAll method in Java searches for a specified string or regex pattern and returns a new string with the matched characters replaced.

Example 1:

class Geeks 
{
    public static void main(String args[]) 
    {  
        String str = new String("Welcome to geeksforgeeks");

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

After replacing regex with replace_str : GFG

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 2: Invalid regex when passed in raplaceAll() method, raises PatternSyntaxException.

import java.io.*;

class Geeks {
    public static void main(String[] args) {
      
        String str = "GFG";
     
        // Incorrect Regular expression
        String regex = "\\";

        // Passing null expression in
        // replaceAll method
        str = str.replaceAll(regex, " ");

        System.out.println(str);
    }
}

Output

Exception in thread "main" java.util.regex.PatternSyntaxException: Unexpected internal error near index 1
    at java.base/java.util.regex.Pattern.error(Pattern.java:2027)
    at java.base/java.util.regex.Pattern.compile(Pattern.java:1788)
    at java.base/java.util.regex.Pattern.<init>(Pattern.java:1428)
    at java.base/java.util.regex.Pattern.compile(Pattern.java:1068)
    at java.base/java.lang.String.replaceAll(String.java:2126)
    at GFG.main(GFG.java:11)

Example 3: The null regular expression is not accepted by the replaceAll() method, it raises the NullPointerException.

import java.io.*;

class Geeks {
    public static void main(String[] args) {
      
        // input string
        String str = "GFG";

        // NULL Regular expression
        String regex = null;

        // Passing null expression in
        // replaceAll method
        str = str.replaceAll(regex, " ");

        System.out.println(str);
    }
}

Output

Exception in thread "main" java.lang.NullPointerException
    at java.base/java.util.regex.Pattern.<init>(Pattern.java:1426)
    at java.base/java.util.regex.Pattern.compile(Pattern.java:1068)
    at java.base/java.lang.String.replaceAll(String.java:2126)
    at GFG.main(GFG.java:11)