Help changing from string to big decimel

[Murphyv10]

Howdy guys
need help changing , from string to a big decimal for my addition method in my calculator , i understand the problem but not the solution . Any help would be great, thanks.

 public void add() 
     {
         BigDecimal oneNumber = model.getDisplay();
         BigDecimal twoNumber = model.getDisplay();
         BigDecimal result = oneNumber.add(twoNumber);



     }

[Murphyv10]

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[NormR1]

i understand the problem

Could you explain what the problem is? Post the full text of any error messages.