HashCodeFunctions.java

import java.util.Arrays;

public class HashCodeFunctions
{
    private final static short DEFAULT_PRIME_NUMBER = 31;
    
    private HashCodeFunctions()
    {
        throw new AssertionError("Could not be instantiated.");
    }

    public static
    int hash(boolean value) { return  (value ? 0 : 1); }

    public static
    int hash(byte value) { return value; }

    public static
    int hash(char value) { return value; }
    
    public static
    int hash(short value) { return value; }

    public static
    int hash(int value) { return value; }

    public static
    int hash(long value) { return ((int) (value ^ (value >> 32))); }

    public static
    int hash(float value) { return hash(Float.floatToIntBits(value)); }
    
    public static
    int hash(double value) { return hash(Double.doubleToLongBits(value)); }
    
    public static
    int hash(Object value) { return value.hashCode(); }
    
    public static
    int hash(boolean[] values) { return Arrays.hashCode(values); }
    
    public static
    int hash(byte[] values) { return Arrays.hashCode(values); }
    
    public static
    int hash(char[] values) { return Arrays.hashCode(values); }
    
    public static
    int hash(short[] values) { return Arrays.hashCode(values); }

    public static
    int hash(int[] values) { return Arrays.hashCode(values); }

    public static
    int hash(long[] values) { return Arrays.hashCode(values); }
    
    public static
    int hash(float[] values) { return Arrays.hashCode(values); }
    
    public static
    int hash(double[] values) { return Arrays.hashCode(values); }

    public static
    int hash(Object[] values) { return Arrays.hashCode(values); }
    
    public static
    int totalHash(int... hashcodes)
    {
        return totalHash(0, DEFAULT_PRIME_NUMBER, hashcodes);
    }

    public static
    int totalHash(int init, short prime, int... hashcodes)
    {
        int result = init;
        for(int hashcode: hashcodes)
            result = result * prime + hashcode;
        return result;
    }
}

MyDomain.java

public class HashCodeTest
{
    long id = 1;
    int age = 30;
    String name = "noname";
    LocalDate birthday = LocalDate.of(1980, 1, 1);
    int[] rates = {1,2,3,4};

    @Override public
    int hashCode()
    {
        return totalHash(hash(id), hash(age), hash(name), hash(birthday), hash(rates));
    }
}