Java String replaceAll()

The Java String class replaceAll() method returns a string replacing all the sequence of characters matching regex and replacement string.

Signature

Parameters

regex : regular expression

replacement : replacement sequence of characters

Returns

replaced string

Exception Throws

PatternSyntaxException: if the syntax of the regular expression is not valid.

Internal implementation

public String replaceAll(String regex, String replacement) {
        return Pattern.compile(regex).matcher(this).replaceAll(replacement);
}

Java String replaceAll() example: replace character

Let's see an example to replace all the occurrences of a single character.

FileName: ReplaceAllExample1.java

public class ReplaceAllExample1{
public static void main(String args[]){
String s1="javatpoint is a very good website";
String replaceString=s1.replaceAll("a","e");//replaces all occurrences of "a" to "e"
System.out.println(replaceString);
}}

Test it Now

Output:

jevetpoint is e very good website

Java String replaceAll() example: replace word

Let's see an example to replace all the occurrences of a single word or set of words.

FileName: ReplaceAllExample2.java

public class ReplaceAllExample2{
public static void main(String args[]){
String s1="My name is Khan. My name is Bob. My name is Sonoo.";
String replaceString=s1.replaceAll("is","was");//replaces all occurrences of "is" to "was"
System.out.println(replaceString);
}}

Test it Now

Output:

My name was Khan. My name was Bob. My name was Sonoo.

Java String replaceAll() example: remove white spaces

Let's see an example to remove all the occurrences of white spaces.

FileName: ReplaceAllExample3.java

public class ReplaceAllExample3{
public static void main(String args[]){
String s1="My name is Khan. My name is Bob. My name is Sonoo.";
String replaceString=s1.replaceAll("\\s","");
System.out.println(replaceString);
}}

Test it Now

Output:

MynameisKhan.MynameisBob.MynameisSonoo.

Java String replaceAll() Method Example 4

The replaceAll() method throws the PatternSyntaxException when there is an improper regular expression. Look at the following example.

FileName: ReplaceAllExample4.java

public class ReplaceAllExample4 
{
// main method
public static void main(String argvs[])
{

// input string
String str = "For learning Java, JavaTpoint is a very good site.";

System.out.println(str);

String regex = "\\"; // the regular expression is not valid.

// invoking the replaceAll() method raises the PatternSyntaxException
str = str.replaceAll(regex, "JavaTpoint ");

System.out.println(str);

}
}

Output:

For learning Java, JavaTpoint is a very good site.

Exception in thread "main" java.util.regex.PatternSyntaxException: Unexpected internal error near index 1
\
	at java.base/java.util.regex.Pattern.error(Pattern.java:2015)
	at java.base/java.util.regex.Pattern.compile(Pattern.java:1784)
	at java.base/java.util.regex.Pattern.(Pattern.java:1427)
	at java.base/java.util.regex.Pattern.compile(Pattern.java:1068)
	at java.base/java.lang.String.replaceAll(String.java:2126)
	at ReplaceExample4.main(ReplaceExample4.java:12)

Java String replaceAll() Method Example 5

The replaceAll() method can also be used to insert spaces between characters.

FileName: ReplaceAllExample5.java

public class ReplaceAllExample5 
{
// main method
public static void main(String argvs[])
{

// input string
String str = "JavaTpoint";
System.out.println(str);

String regex = "";
// adding a white space before and after every character of the input string.
str = str.replaceAll(regex, " ");

System.out.println(str);

}
}

Output:

JavaTpoint
 J a v a T p o i n t

Java String replaceAll() Method Example 6

Even the null regular expression is also not accepted by the replaceAll() method as the NullPointerException is raised.

FileName: ReplaceAllExample6.java

public class ReplaceAllExample6 
{
// main method
public static void main(String argvs[])
{

// input string
String str = "JavaTpoint";
System.out.println(str);

String regex = null; // regular expression is null

str = str.replaceAll(regex, " ");

System.out.println(str);

}
}

Output:

JavaTpoint

Exception in thread "main" java.lang.NullPointerException
	at java.base/java.util.regex.Pattern.(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 ReplaceAllExample6.main(ReplaceAllExample6.java:13)

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