How to convert given string in comma seperated characters in java?

You can also do it on a higher level without writing your own loop. It's not faster or anything, but the code is more clear about what it's doing: "Split my string into characters and join it back together, separated by commas!" ...

String name = "String";
String separated = String.join(",", name.split(""));
System.out.println(separated);

EDIT: String.join() is available from Java 1.8 and up.

I would personally use a StringBuilder for this task.

What you need, is to apply some logic that can distinguish whether or not a comma is needed. You loop through the characters just like you did and you always append a comma before the next character, except on the first iteration.

Example:

public static void main(String[] args) {
    String test = "String";
    StringBuilder sb = new StringBuilder();
    for (char ch : test.toCharArray()) {
        if (sb.length() != 0) {
            sb.append(",");
        }
        sb.append(ch);
    }
    System.out.println(sb.toString());
}

Output:

S,t,r,i,n,g

Another way without StringBuilder and using just a traditional for loop, but using the same logic:

public static void main(String[] args) {
    String test = "String";
    char[] chars = test.toCharArray();
    for (int i = 0; i < chars.length; i++) {
        if (i != 0) {
            System.out.print(",");
        }
        System.out.print(chars[i]);
    }
}

Output:

S,t,r,i,n,g

Sure, but for this you need a for loop based on the length of c, other solutions are not as straight IMHO:

String name="String";
char[] c = name.toCharArray();
for (int i = 0; i < c.length; i++){
    char ch = c[i];
    System.out.print(ch);
    if( i != c.length -1 ){
        System.out.print(",");
    }
}

Some additional 2 Cents:

You can stream the character int values, map them to a List<String> where each element is a single char as String and finally use String.join(..., ...) in order to get the desired result, a comma separated String of all the characters in the original String:

public static void main(String[] args) {
    // take an example String
    String name = "Stringchars";
    // make a list of characters as String of it by streaming the chars
    List<String> nameCharsAsString = name.chars()
                                        // mapping each one to a String
                                        .mapToObj(e -> String.valueOf((char) e))
                                        // and collect them in a list
                                        .collect(Collectors.toList());
    // then join the elements of that list to a comma separated String
    String nameCharsCommaSeparated = String.join(",", nameCharsAsString);
    // and print it
    System.out.println(nameCharsCommaSeparated);
}

Running this code results in the following output:

S,t,r,i,n,g,c,h,a,r,s

This is just another possibility of getting your desired result, it is not necessarily the best solution.

You can use Stream to do that. Please check below,

String result = Arrays.stream(name.split("")).collect(Collectors.joining(","));

Output:

S,t,r,i,n,g