Java String replaceAll() replaces all the occurrences of a particular character, string or a regular expression in the string. The method returns a new string as its output. The method requires two parameters.
String replaceAll() Syntax
public String replaceAll(String regex, String replacement)
A regex that represents the pattern to look for while replacing and a replacement string to replace it with.
There are multiple types of substitutions that are possible with String replaceAll() method.
Replacing a single character
To replace a single character, specify the character to be replaced as the regex.
public class Main {
public static void main(String[] args) {
String s = "Welcome to JournalDev";
System.out.println("Original String : "+s);
System.out.println();
String rep = s.replaceAll("o","@");
System.out.println("New String: "+rep);
}
}
Original String: Welcome to JournalDev
New String: Welc@me t@ J@urnalDev
Replace sequence of characters
To replace a sequence of characters, mention the sequence as the regex in the replaceAll() function.
public class Main {
public static void main(String[] args) {
String s = "Welcome to JournalDev";
System.out.println("Original String : "+s);
System.out.println();
String rep = s.replaceAll("to","this is");
System.out.println("New String: "+rep);
}
}
Original String : Welcome to JournalDev
New String: Welcome this is JournalDev
Remove/Replace Spaces
The replaceAll() method can remove or replace the whitespaces in your text string.
public class Main {
public static void main(String[] args) {
String s = "Welcome to JournalDev";
System.out.println("Original String : "+s);
System.out.println();
String rep = s.replaceAll(" ","");
System.out.println("New String: "+rep);
}
}
Original String : Welcome to JournalDev
New String: WelcometoJournalDev
Similarly, to replace the whitespaces:
public class Main {
public static void main(String[] args) {
String s = "Welcome to JournalDev";
System.out.println("Original String : "+s);
System.out.println();
String rep = s.replaceAll(" ","_");
System.out.println("New String: "+rep);
}
}
Original String : Welcome to JournalDev
New String: Welcome_to_JournalDev
Hiding numeric digits in a text
The replaceAll() can hide numeric digits that appear in a string. The digits can be replaced by ‘*’.
public class Main {
public static void main(String[] args) {
String s = "Hello! this is the number : 1234 ";
System.out.println("Original String : "+s);
System.out.println();
String rep = s.replaceAll("[0-9]","*");
System.out.println("New String: "+rep);
}
}
Original String : Hello! this is the number : 1234
New String: Hello! this is the number : ****
Creating custom messages
replaceAll() can replace the strings in a generic string to generate a custom message. Let’s take values from a map and generate a custom message.
import java.util.HashMap;
import java.util.Map;
public class Main {
public static void main(String[] args) {
String s = "dear #Employee#, your Current Salary is #Salary#.";
Map<String, String> vals = new HashMap<String, String>();
vals.put("#Employee#", "John");
vals.put("#Salary#", "12000");
for (String key : vals.keySet()) {
s = s.replaceAll(key, vals.get(key));
}
System.out.println(s);
}
}
dear John, your Current Salary is 12000.
Replace First
Unlike replceAll(), replaceFirst() only replaces the first instance of the pattern.
public class Main {
public static void main(String[] args) {
String s = "Welcome to JournalDev";
System.out.println("Original String : "+s);
System.out.println();
String rep = s.replaceFirst("o","@");
System.out.println("New String: "+rep);
}
}
Original String: Welcome to JournalDev
New String: Welc@me to JournalDev
Conclusion
The replaceAll() method replaces a regex with a string. This is different from the simple replace() method that only performs character substitutions. You can learn more about the repalceAll() function from its official documentation.
Thank you 🙂
Very nice example! Thanks.