Create hash from string and int

Question

I remember eclipse and idea have this template to automatically create an object's hashCode based on its attributes.

One of the strategies if a number and a string is used is something like this.

  return stringValue.hashCode() + intValue * 32;

Ooor something like that.

I don't have nor eclipse or idea at hand and I would like to create such function.

EDIT

Based on the answers I create this mini-class

    class StringInt {
        private final String s;
        private final int i;

        static StringInt valueOf( String string , int value ) {
            return new StringInt( string, value );
        }
        private StringInt( String string, int value ) {
            this.s = string;
            this.i = value;
        }
        public boolean equals( Object o ) {
            if( o != null && o instanceof StringInt ){
                StringInt other = ( StringInt ) o;
                return this.s == other.s && this.i == other.i;
            }

            return false;
        }
        public int hashCode() {
            return s != null ? s.hashCode() * 37 + i : i;
        }
    }

This class is to be used as key for a large memory map ( > 10k elements ) I don't want to iterate them each time to find if the String and the int are the same.

Thank you.

ps.. mmh probably it should be names StringIntKey.

Answer 1

Use the Apache Commons HashcodeBuilder:

public int hashCode() {
    new HashCodeBuilder(17, 37).
           append(myString).
           append(myInt);
}

Link here: http://commons.apache.org/lang/api-2.3/org/apache/commons/lang/builder/HashCodeBuilder.html

And here:

http://www.koders.com/java/fidCE4E86F23847AE93909CE105394B668DDB0F491A.aspx

Answer 2

Eclipse always does roughly the same hashing function, here's an example for a class with an in and String as fields

    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + this.interger;
        result = prime * result + ((this.string == null) ? 0 : this.string.hashCode());
        return result;
    }

They always pick 31 as the prime, and then multiple by build in hash functions or the value if its a primitive. Something like this wouldn't be hard to create as a method.

     public int hashCode(Object ... things) {
         final int prime = 31;
         int result = 1;
         for(Object thing : things) {
             result = prime * result + thing.hashCode();
         }
         return result;
     }