Java String Replace Character

Java String replace character example shows how to replace a character in the string using the replace and replaceFirst methods of the String class.

How to replace a character in a string?

The Java String class provides the replace method that takes two char arguments that can be used to replace a character in a string.

1	public String replace(char oldCharacter, char newCharacter)

This method replaces all occurrences of the old character with the new one in the string.

package com.javacodeexamples.stringexamples;

public class StringReplaceCharacter {

public static void main(String[] args) {

String str = "cat";

System.out.println( str.replace('c', 'b') );

}

Output

bat

As you can see from the output, the character ‘c’ is replaced with the character ‘b’ in the string. Instead of the character version of the replace method, you can also use the overloaded replace method that accepts two string arguments instead of the character arguments like given in the below code example.

1 2	String str = "cat"; System.out.println( str.replace("c", "b") );

Output

bat

The replace method replaces all the old characters in the string with the new one. See below given example.

1 2	String str = "cat can"; System.out.println( str.replace("c", "b") );

Output

bat ban

If you want to replace only the first instance of the character with the new one, you can use the replaceFirst method instead of the replace method.

1	public String replaceFirst(String regex, String replacement)

Here is the same example with the replaceFirst method instead of the replace method.

1 2	String str = "cat can"; System.out.println( str.replaceFirst("c", "b") );

Output

bat can

As you can see from the output, only the first instance of the character ‘c’ was replaced in the string.

Additionally, the replace method is case-sensitive. It means that the case of the character to replace must be the same, otherwise, the replacement will not happen.

1 2	String str = "Cat"; System.out.println( str.replaceFirst("c", "b") );

Output

Cat

As you can see from the output since the case of the character we want to replace does not match with the case of the character in the string, no replacement was done. If you want to do the replacement regardless of the case, you can either convert the string to uppercase or to lowercase and then do the replacement as given below.

1 2	String str = "Cat"; System.out.println( str.toLowerCase().replaceFirst("c", "b") );

Output

bat

Lastly, both the replace and replaceFirst methods return a new string having replaced content. The original string object remains as-is.

String str = "cat";

System.out.println( str.replace("c", "b") );

System.out.println(str);

Output

bat

cat

If you want the replacement results back in the original string object, you need to assign the return value of these methods to the original string reference as given below.

String str = "cat";

str = str.replace("c", "b");

System.out.println(str);

Output

bat

If you want to learn more about the string in Java, please visit the Java String tutorial.

Please let me know your views in the comments section below.

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Rahim

I have a master's degree in computer science and over 18 years of experience designing and developing Java applications. I have worked with many fortune 500 companies as an eCommerce Architect. Follow me on LinkedIn and Facebook.

How to replace a character in a string?

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