Integer.parseInt(a+1); parses the String that results from concatenating the value of the String a (“1”) to the int literal 1, which is “11”.
Change it to
int inc = Integer.parseInt(a) + 1;
This way “a” would be parsed to the integer 1 and then 1 would be added to it to give you the value 2.
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solved How to increment the string value? [duplicate]