java replace only one character in a string code example

Example 1: how to replace a character with another character in a string in java

public class JavaExample{
   public static void main(String args[]){
	String str = new String("Site is BeginnersBook.com");

	System.out.print("String after replacing com with net :" );
	System.out.println(str.replaceFirst("com", "net"));

	System.out.print("String after replacing Site name:" );
	System.out.println(str.replaceFirst("Beginners(.*)", "XYZ.com"));
   }
}

Example 2: java replaceall single character

.replaceAll("(?<!\\S)[^ ](?!\\S)", " ").trim()