how to replace a character with another character in a string in java

1//short answer: you cannot individually change any specific character
2//of a String in java. You can however do this:
3
4String s1 = "This is a String";
5String s2 = s1.substring(0, 8) + "o" + s1.substring(9);
6System.out.println(s2);
7//Prints "This is o String", replaced the 8th character with an o

1String str = ".............................."; 
2
3        int index = 5; 
4  
5        char ch = '|'; 
6 
7        StringBuilder string = new StringBuilder(str); 
8        string.setCharAt(index, ch); 
9
10        System.out.println(string); 

1public class JavaExample{
2   public static void main(String args[]){
3	String str = new String("Site is BeginnersBook.com");
4
5	System.out.print("String after replacing com with net :" );
6	System.out.println(str.replaceFirst("com", "net"));
7
8	System.out.print("String after replacing Site name:" );
9	System.out.println(str.replaceFirst("Beginners(.*)", "XYZ.com"));
10   }
11}