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A question about equals() method

 
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Hi!everyone.
I see Sun Certified Programmer for Java 2 Study Guide and it says that if you want objects of your class to be used as keys for a hashtable then you must override equals().But why I can put a class defined by myself into HashTable?

why the following sample has overridden equals() and hashcode() but printed "test null" rather than "test test"?

 
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The C in hashCode should be upper case. You have used lower case characters, so you really did not override the hashCode method.
 
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