I have 2 files with different names but the same content. When I create streams of these files and use the FileInputStream.HashCode(); method to find the hash value I receive different values
Can somebody provide me with the correct API if possible for the hash method in Java that receives the same hash values for files with the same content.
It sounds like a Cryptographic Hash Function will meet your needs.
The Apache Commons Codec library has a utility class for creating cryptographic hash values (a.k.a., message digests) called DigestUtils. For example, the sha256 method takes an InputStream and returns a SHA-256 message digest as a byte array.
FileInputStream has no method named hashCode(). It use the general Object.hasCode() method.
Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.
The general contract of hashCode is:
- Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
- If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
- It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)
FileInputStream.HashCode() inherits the hashCode from Object which is the internal address. It does not take content into account.
Also if you want to compare 2 files for equality why would you want to use a hashfunction?
2 strings that are different can have the same hash code due to colision. Same with the contents of files.
You can use FileUtils.contentEquals(file1, file2); if you can use a third party library (Commons IO)
String and compare the hashCode of the String?String have the same contents they must have the same hashCode.Not sure what you mean