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Java Forum / General / August 2007return hash-code of a string
Hello. Is there any hash function in Java, that convert a string value to a hash code ? Thanks :) And thus spoke Eitan M... > Is there any hash function in Java, that convert a string value to a hash > code ? String xyz = "Hello World"; int hash = xyz.hashcode(); > And thus spoke Eitan M... > [quoted text clipped - 3 lines] > String xyz = "Hello World"; > int hash = xyz.hashcode(); Should be hashCode(), with an upper-case C. int hash = "Hello World".hashCode(); also works.  SignatureEric Sosman esosman@ieee-dot-org.invalid And thus spoke Eric Sosman... > Should be hashCode(), with an upper-case C. Correct, my fault. Flo Hash code returns an integer, and due that it is limited (it is not CRC), so a string like : "zzzzz" may have an exception. > And thus spoke Eric Sosman... > [quoted text clipped - 3 lines] > > Flo > Hash code returns an integer, Please do not top-post (placement of your reply above the material to which you're replying). > and due that it is limited (it is not CRC), What is the limitation that concerns you, and how does it cause trouble? Why is CRC needed? > so a string like : "zzzzz" may have an exception. What sort of exception do you mean? "Flo 'Irian' Schaetz" <iryan@gmx.de> wrote in message And thus spoke Eric Sosman... >>> hashCode() By definition, a hash reduces information from a source (document, byte sequence, ...). That is, in fact, the point of a hash code in the first place. The reduced information set is easier to manipulate than the source domain set, and by dint of being int, faster, too. Not to put to fine a point on it, hash codes are a hack to compensate for human impatience. This aside from their cryptographic utility, but that's not essential to Object.hashCode(). So if you want a hash code, you want to reduce information. There's no point in asking for a hash code that doesn't reduce information. SignatureLew > Hash code returns an integer, Please do not top-post (placement of your reply above the material to which you're replying). > and due that it is limited (it is not CRC), What is the limitation that concerns you, and how does it cause trouble? Why is CRC needed? > so a string like : "zzzzz" may have an exception. What sort of exception do you mean? "Flo 'Irian' Schaetz" wrote And thus spoke Eric Sosman... >> hashCode() By definition, a hash reduces information from a source (document, byte sequence, ...). That is, in fact, the point of a hash code in the first place. The reduced information set is easier to manipulate than the source domain set, and by dint of being int, faster, too. Not to put too fine a point on it, hash codes are a hack to compensate for human impatience. This aside from their cryptographic utility, but that's not essential to Object.hashCode(). So if you want a hash code, you want to reduce information. There's no point in asking for a hash code that doesn't reduce information. SignatureLew [Top posting changed] >> And thus spoke Eric Sosman... >> [quoted text clipped - 5 lines] > >Hash code returns an integer, Of course hashCode() returns an integer, that is what it does. If you do not want an integer then do not use hashCode(). >and due that it is limited (it is not CRC), If you want a CRC then use a CRC. >so a string like : "zzzzz" may have an exception. I am not clear what you mean here. On my system "zzzzz".hashCode() returns 116425210 rossum > Hash code returns an integer, > and due that it is limited (it is not CRC), > so a string like : "zzzzz" may have an exception. If I understand you correctly, what you are trying to say is that for very long Strings, hashCode will fail with an exception. That is not true: hashCode will only fail on a null object (for different reasons); and the hash code will always be integral but not necessarily positive (which is true for all objects). If you want a guaranteed positive hash code, then use Math.abs(obj.hashCode()). In short: hashCode will always return (except for null objects) an integral value for any Java built-in object (negating bugs) and should do so for any Java object. I don't understand what you mean by "limited", though. SignatureBeware of bugs in the above code; I have only proved it correct, not tried it. -- Donald E. Knuth Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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