The String replace() method returns a new string after replacing all the old characters/CharSequence with a given character/CharSequence.
Example:
Return a new string where all " o" characters are replaced with "p" character:
Java
// Java program to demonstrate
// the replace() method
public class Main {
public static void main(String[] args) {
// Define an original string
String originalString = "Hello World";
// Replace 'o' with 'p' in the original string
String replacedString = originalString.replace("o", "p");
// Print the replaced string
System.out.println(replacedString);
}
}
Syntax
public String replace(char oldch, char newch)
Parameters
- oldch: the old character.
- newch: the new character.
Return Value
- It returns a string derived from this string by replacing every occurrence of oldch with newch.
Exception
- NullPointerException- replace() method returns this exception when the target char/CharSequence is null.
Java String replace() Examples
The following examples demonstrate how to use the replace() method in Java:
Example 1: Java String replace(char old, char new) Method
To show the working of replace(char old, char new).
Java
// Java code to demonstrate the
// working of replace()
public class rep1 {
public static void main(String args[])
{
// Initialising String
String Str = new String("Welcome to geeksforgeeks");
// Using replace to replace characters
System.out.print("After replacing all o with T : ");
System.out.println(Str.replace('o', 'T'));
// Using replace to replace characters
System.out.print("After replacing all e with D : ");
System.out.println(Str.replace('e', 'D'));
}
}
OutputAfter replacing all o with T : WelcTme tT geeksfTrgeeks
After replacing all e with D : WDlcomD to gDDksforgDDks
Example 2: Java String replace(String target, String replacement) Method
We can implement the replace() method with substring/CharSequence just like with char.
To show the working of the replace(String target, String replacement) method.
Java
// Java Program to implement
// replace() method
import java.io.*;
class GFG {
public static void main(String[] args)
{
String s1 = "GeeksforGeeks";
// orignal string
System.out.println(s1);
// Replace Geeks with Gfg
String replaceString = s1.replace("Geeks", "GfG ");
// New String
System.out.println(replaceString);
}
}
OutputGeeksforGeeks
GfG forGfG
Example 3:
The null regular expression is not accepted by the replace() method, it raises the NullPointerException.
Java
// Java Program to implement
// Java replaceAll() method
import java.io.*;
// Driver Class
class GFG {
// Main function
public static void main(String[] args)
{
String str = "GeeksforGeeks";
int size = str.length();
System.out.println(str);
String target = null;
// replacing null with GFG
str = str.replace(target, "GFG");
System.out.println(str);
}
}
Output
Exception in thread "main" java.lang.NullPointerException
at java.base/java.lang.String.replace(String.java:2142)
at GFG.main(GFG.java:12)
String replace() Method - Java Programs
Let's see some coding problems and solve them with the String charAt() method in Java.
1. Replace Substrings in a String Using the replace() Java method
Java
public class WordReplacement {
public static void main(String[] args) {
String sentence = "We are learning JavaScript";
String wordToReplace = "JavaScript";
String replacementWord = "Java";
System.out.println("Original sentence: " + sentence);
String replacedSentence = replaceWord(sentence, wordToReplace, replacementWord);
System.out.println("Replaced sentence: " + replacedSentence);
}
// Method to replace all occurrences of a word in a sentence
private static String replaceWord(String sentence, String wordToReplace, String replacementWord) {
// Use replaceAll() method to replace all occurrences
return sentence.replaceAll("\\b" + wordToReplace + "\\b", replacementWord);
}
}
OutputOriginal sentence: We are learning JavaScript
Replaced sentence: We are learning Java
2. Replace Spaces with Underscores Using the replace() Java method
Java
public class ReplaceSpacesExample {
public static void main(String[] args) {
String sentence = "Geeks for Geeks";
String replacedSentence = replaceSpaces(sentence);
System.out.println("Replaced sentence: " + replacedSentence);
}
// Method to replace spaces with underscores
private static String replaceSpaces(String sentence) {
return sentence.replace(" ", "_");
}
}
OutputReplaced sentence: Geeks_for_Geeks
References
To know more about more String Methods refer to the article Java String Methods
Whether you are a beginner starting Java programming or an experienced looking to brush up on your Java skills, this tutorial will provide you with a deep understanding of the replace function and its uses in Java.
The charAt method in Java is a fundamental function for string manipulation. With this guide, you can easily access the characters of a string using the replace function.
