You can just split the string..

public String[] split(String regex)

Note that java.lang.String.split uses delimiter's regular expression value. Basically like this...

String filename = "abc.def.ghi";     // full file name
String[] parts = filename.split("\\."); // String array, each element is text between dots

String beforeFirstDot = parts[0];    // Text before the first dot

Of course, this is split into multiple lines for clairity. It could be written as

String beforeFirstDot = filename.split("\\.")[0];

You can do this:

String str = "123dance456";
String substr = "dance";
String before = str.substring(0, str.indexOf(substr));
String after = str.substring(str.indexOf(substr) + substr.length());

Or

String str = "123dance456";
String substr = "dance";
String[] parts = str.split(substr);
String before = parts[0];
String after = parts[1];

It is noteworthy that the second answer not work if we have more than one occurrence of the substring. To that end, if we only want the first one to be recognized, it would be safer to call split with a limit:

String[] parts = str.split(substr, 2);

which ensures that the returned array has at most two elements. Also, since split will interpret its input as a regular expression we have to be wary of invalid regular expression syntax. As such, I would much rather the first solution, since it works irrespective of the composition of the original substring.

To make the first answer more efficient -- as it is my preferred answer -- then, we would need to remember the position of the substring:

final int position = str.indexOf(substr);
if (position >= 0) {
    //if the substring does occur within the string, set the values accordingly
    before = str.substring(0, position);
    after = str.substring(position + substr.length());
} else {
    //otherwise, default to the empty string (or some other value)
    before = "";
    after = "";
}

It always pays to pay attention to these little edge cases.

String splitted[] =s.split(",",2); // will be matched 1 times. 

splitted[0]  //before the first comma. `abc`
splitted[1]  //the whole String after the first comma. `cde,def,fgh`

If you want only cde as the string after first comma. Then you can use

String splitted[] =s.split(",",3); // will be matched  2 times

or without the limit

String splitted[] =s.split(",");

Don't forget to check the length to avoid ArrayIndexOutOfBound.