[求助]a problem, please help

i m currently doing my assignment, and the whole thing s about a word guessing game, part of it is like:
it is got a destination list, and then ask the user to input a destination, either is upper or lower case, so that the user will get to that destination, and when the user put an invalid destination, which means not in the list. the program should keep asking the user to input the destination until a valid one, and my question is, how can i tell if the user has input an invalid destination, someone told me to use a loop , checking using StringTokenizer to seperate destination list, and i tried, but it didnt work! so anyone help me???? and i m sure u have to use loop. coz thats what we been taught recently!
THANKS SO MUCH!!!
for example,
Destination list: B,C,E,
Enter the destination: F
Enter the destination: k
Enter the destination: o
Enter the destination: v
and so on.........
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我学的JAVA都是用英文的，如果你们都讲中文的名词，我都看不懂！！真的很对不起，我的英文很不好，没有什么别的意思，谢谢，大家帮帮我！！！！！！ASSIGNMENT交不了了！！！！

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it's my baby! the java section of chinese download by www.zasp.net.

I had a english-java section for your study, shall you ?

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英文不好怎么还学 英文的java

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看了之后那是相当的自卑，。
回家学英语了。

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