How to check a string contains only digits and one occurrence of a decimal point?

Question

My idea is something like this but I dont know the correct code

if (mystring.matches("[0-9.]+")){
  //do something here
}else{
  //do something here
}

I think I'm almost there. The only problem is multiple decimal points can be present in the string. I did look for this answer but I couldn't find how.

Answer 1

If you want to -> make sure it's a number AND has only one decimal <- try this RegEx instead:

if(mystring.matches("^[0-9]*\\.?[0-9]*$")) {
    // Do something
}
else {
    // Do something else
}

This RegEx states:

1. The ^ means the string must start with this.
2. Followed by none or more digits (The * does this).
3. Optionally have a single decimal (The ? does this).
4. Follow by none or more digits (The * does this).
5. And the $ means it must end with this.

Note that bullet point #2 is to catch someone entering ".02" for example.

If that is not valid make the RegEx: "^[0-9]+\\.?[0-9]*$"

• Only difference is a + sign. This will force the decimal to be preceded with a digit: 0.02