Could it be that the number is > Integer.MAX_VALUE? If I try your code with Long instead, it works.

It's because 3020857508 exceeds Integer.MAX_VALUE. You should use long to convert the string to number.

java> String n="3020857508";
//=> java.lang.String n = "3020857508"
java> Integer a = Integer.parseInt(n.trim());
//=> java.lang.NumberFormatException: For input string: "3020857508"
java> Integer.MAX_VALUE
//=> java.lang.Integer res2 = 2147483647
java> Long a = Long.parseLong(n.trim());
//=>java.lang.Long a = 3020857508

The above is javarepl output.

If you are using JDK9 or above, you can see the same result in jshell.

jshell> String n="3020857508"
n ==> "3020857508"

jshell> Integer a = Integer.parseInt(n.trim())
|  Exception java.lang.NumberFormatException: For input string: "3020857508"
|        at NumberFormatException.forInputString (NumberFormatException.java:65)
|        at Integer.parseInt (Integer.java:652)
|        at Integer.parseInt (Integer.java:770)
|        at (#2:1)

jshell> Integer.MAX_VALUE
$3 ==> 2147483647

jshell> Long a = Long.parseLong(n.trim());
a ==> 3020857508

This exception say :

java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(Unknown Source)

your input string here is set to "" aka an empty String and then you try to parse the "" into an int. And that is not possible and therefore the error.

Make sure you pass in correct numbers like 1 2 3 or something and with no dots like 1.2 because that aswell will give an error.

You should also add some logic so its not possible to pass in an empty string or catch the empty string or a double value. Because it will cause this exception everytime user does not input a correct number format.