java - Run-time error. Integer convert to string -

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i creating program returns ordinal form of number (1st, 2nd etc.). when run program runtime error.

i suspecting has converting int string, can't seem find source of problem.

public void run() {         ordinalform(5);     }      private string ordinalform(int num) {         string number = integer.tostring(num);         string correctword ="";         if((number.charat(number.length()-2)=='1'                 && number.charat(number.length()-1)=='1')){             correctword=number+"th";         } else if (number.charat(number.length()-2)=='1'                 && number.charat(number.length()-1)=='2') {             correctword=number+"th";         } else if ((number.charat(number.length()-1)=='1'                 && number.charat(number.length()-1)=='3')) {             correctword=number+"th";         } else if(number.charat(number.length()-1)=='1') {             correctword=number+"st";         } else if(number.charat(number.length()-1)=='2') {             correctword=number+"nd";         } else if(number.charat(number.length()-1)=='3') {             correctword=number+"rd";         } else {             correctword=number+"th";         }         println(correctword);         return correctword;     } }

the error: exception in thread "thread-1" java.lang.stringindexoutofboundsexception: string index out of range: -1 @ java.lang.string.charat(string.java:646) @ stringtraining.ordinalform(stringtraining.java:17) @ stringtraining.run(stringtraining.java:11) @ acm.program.program.runhook(program.java:1568) @ acm.program.program.startrun(program.java:1557) @ acm.program.appletstarter.run(program.java:1895) @ java.lang.thread.run(thread.java:745)

edit:

you calling method number 5 parameter :

ordinalform(5);

the first instruction executes in ordinalform function :

string number = integer.tostring(num);

this converts variable num (equals 5) string. number equal "5". notice number.length() equal 1 now.

next in condition:

if((number.charat(number.length()-2)=='1' && ....) { }

number.length() equal 1 (number == "5"). therefore, number.length() - 2 equal -1. technically, trying is:

if((number.charat( -1 )=='1' && ....) { }

and since there no such thing index -1, stringindexoutofboundsexception thrown, , execution fails.


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