// validating/Inverter4.java

// (c)2021 MindView LLC: see Copyright.txt

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

package validating;

import static java.lang.Character.*;

public class Inverter4 implements StringInverter {

static final String ALLOWED =

"abcdefghijklmnopqrstuvwxyz ,." +

"ABCDEFGHIJKLMNOPQRSTUVWXYZ";

@Override public String invert(String str) {

if(str.length() > 30)

throw new RuntimeException("argument too long!");

String result = "";

for(int i = 0; i < str.length(); i++) {

char c = str.charAt(i);

if(ALLOWED.indexOf(c) == -1)

throw new RuntimeException(c + " Not allowed");

result += isUpperCase(c) ?

toLowerCase(c) :

toUpperCase(c);

}

return result;

}

}