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From: Lew <lewbloch@gmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: I need a different approach - suggestions please
Date: Tue, 26 Jun 2012 14:32:15 -0700 (PDT)
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markspace wrote:
> bilsch wrote:
> 
> > Now that you mention it I see how that would work.  However the actual
> > program has many non-numeric buttons I don't want in the string - I
> > better leave that alone for the present.
> 
> 
> A couple of things.  First, even if true, it's better to do something 
> like this:
> 
>    if( btn == "1" || btn == "2" || btn == "3" ... )
>    {
>        // one single case here...
>    }
> 
> Than it is to use many different if-blocks.  Same action for different 
> inputs, you want to use one code block to implement that action.
> 
> One other important point I'd like to make is that Java strings don't 
> normally compare with ==.  You have to use .equals() instead.  Your code 
> works now because all of the strings are in a single file, but as your 
> program grows == will no longer work for you.
> 
> This is the normal, and more correct, way to do it:
> 
>    if( btn.equals( "1" ) || btn.equals( "2" ) || ... )
>    {
>       strng1 += btn;
>    }

  switch (btn) 
  {
    case "1":
    case "2": 
        doCaseOneAndTwo();
        break;

    case "3": 
        doCaseThree();
        break;

    default:
        doAllOtherCases();
        break;
  }

> Lastly, given your specific use case, there's a cheap quick way to cut 
> down on verbosity.  It involves knowing the API well, but String and 
> Math (and a few others) are two APIs that you should memorize eventually 
> to be a good Java programmer.  (Other APIs it's OK to have to consult 
> the documentation periodically.)

Also you should be very, very familiar with the collections classes 
(mostly in java.util.*).

>    String digits = "0123456789.";
>    String opers = "+-/*";
>    String clear = "Clear";
> 
>    if( digits.contains( btn ) ) {
>       strng1 += btn;
>    } else if( opers.contains( btn ) ) {
>       // go do some math
>    } else if( clear.equals( btn ) ) {
>       strng1 = "0";
>    }
> 
> Note the above block is untested. Caveat emptor.
> 
> Later you'll be able to do the same thing with objects that aren't 
> strings with the Set class.
> 
>    Set stuff1 = ...
> 
>    if( stuff1.contains( potentialMember ) ) {
>       // take an action...
>    }

-- 
Lew