Java String replaceAll() Method

The String replaceAll method in Java searches for a specified string or a specified value, or a regex expression by virtue of which has the same suggests returns a new string with related characters. Let us learn about Java replaceAll string method in this article. 

Java String replaceAll()

This method replaces each substring of the string that matches the given regular expression with the given replace_str. 

Syntax of Java replaceAll String

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 of String.replaceAll Method in Java

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

Exceptions with String.replaceAll Java

Although the String replaceAll method is very effective in Java but even it comes up with certain exceptions as mentioned below:

1. Invalid regex 

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

Example:

Java

// Java Program to demonstrate
// replaceAll() method
import java.io.*;

// Driver class
class GFG {
    // main function
    public static void main(String[] args)
    {
        // input string
        String str = "GFG";
        System.out.println(str);

        // NULL 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)

2. Null regular expression

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

Example:

Java

// Java Program to demonstrate
// replaceAll() method
import java.io.*;

// Driver class
class GFG {
    // main function
    public static void main(String[] args)
    {
        // input string
        String str = "GFG";
        System.out.println(str);

        // 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)