Package org.biojava.nbio.core.util

Class Hashcoder

  • public class Hashcoder
extends Object
    Contains helper methods for generating a HashCode without having to resort to the commons lang hashcode builders. Example where the property name is a String and the property age is an int 
     public int hashCode() {
   int result = Hashcoder.SEED;
   result = Hashcoder.hash(result, this.getName());
   result = Hashcoder.hash(result, this.getAge());
   return result;
 }
    Author:
    ayates

    • Field Summary

      Fields 
      Modifier and Type Field Description
      static int PRIME
      The prime number used to multiply any calculated hashcode seed by i.e. result = PRIME*result + c Where result is the result of the previous calculation (at first this will be seed) and c is the calculated int to add to result
      static int SEED
      An initial value for a hashCode, to which we add contributions from fields.

    • Constructor Summary

      Constructors 
      Constructor Description
      Hashcoder()  

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      static int hash​(int seed, boolean b)  
      static int hash​(int seed, char c)  
      static int hash​(int seed, double d)
      double support which is done using the same techinque as float hashing except we convert to a long not to an int.
      static int hash​(int seed, float f)
      float support done via Float.floatToIntBits(float) which allows the encoding of a float as an int.
      static int hash​(int seed, int i)
      Used for ints, bytes and shorts
      static int hash​(int seed, long l)
      long support done by shifting by 32 (using unsigned shift)
      static int hash​(int seed, Object o)
      o is a possibly-null object field, and possibly an array.

    • Field Detail

      • SEED

        public static final int SEED
        An initial value for a hashCode, to which we add contributions from fields. Using a non-zero value decreases collisions of hashCode values.
        See Also:
        Constant Field Values

      • PRIME

        public static final int PRIME
        The prime number used to multiply any calculated hashcode seed by i.e. result = PRIME*result + c Where result is the result of the previous calculation (at first this will be seed) and c is the calculated int to add to result
        See Also:
        Constant Field Values

    • Method Detail

      • hash

        public static int hash​(int seed,
                       boolean b)

      • hash

        public static int hash​(int seed,
                       char c)

      • hash

        public static int hash​(int seed,
                       int i)
        Used for ints, bytes and shorts

      • hash

        public static int hash​(int seed,
                       long l)
        long support done by shifting by 32 (using unsigned shift)

      • hash

        public static int hash​(int seed,
                       float f)
        float support done via Float.floatToIntBits(float) which allows the encoding of a float as an int. We can then hash as normal.

      • hash

        public static int hash​(int seed,
                       double d)
        double support which is done using the same techinque as float hashing except we convert to a long not to an int.

      • hash

        public static int hash​(int seed,
                       Object o)
        o is a possibly-null object field, and possibly an array. If o is an array, then each element may be a primitive or a possibly-null object.