java - How can I find the sum of two numbers which are in String variables?

Question

In this code fragment, I can't sum a and b:

String a = "10";
String b = "20"; 
JOptionPane.showMessageDialog(null,a+b);

Since a and b are defined as String, this code will concatenate the strings and output 10+20=1020.

How can I get it to instead sum a and b and output 10+20=30?

Answer 1

Java provides parse methods for Primitive Types. So depending on your input you can use Integer.parseInt, Double.parseDouble or others.

String result;
try{
 int value = Integer.parseInt(a)+Integer.parseInt(b);
 result = String. valueOf(value) ;
}catch(NumberFormatException ex){
 //either a or b is not a number
 result = "Invalid input";
}
JOptionPane.showMessageDialog(null,result);