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);
         


        

Answer 1

Integer wrapper class has constructor which takes String parameter representing numbers.

String a= txtnum1.getText();//a="100"
String b= txtnum2.getText();//b="200" 

Integer result;
int result_1;
String result_2;

try{
result = new Integer(a) + new Integer(b); // here variables a and b are Strings representing numbers. If not numbers, then new Integer(String) will throw number format exception.

int result_1=result.intValue();//convert to primitive datatype int if required.

result_2 = ""+result; //or result_2 = ""+result_1; both will work to convert in String format

}catch(NumberFormatException ex){
//if either a or b are Strings not representing numbers
result_2 = "Invalid input";
}