Accessing HashMaps

[Jeremy Donaldson]

I'm continuing to work on the Assignment OOP-2 and I've come across another delima. I'm trying to access the value of a hashmap by passing a string value. I've since found that it doesn't like that. It obviously requires an argument of type object. Why doesn't automatic promotion work in this case. Then I'm trying to return the value from the hashmap as an int. This again does not work and it doesn't allow me to cast down from an object to an int or Integer.
Here is a portion of the code that compiles but gives me the following runtime exception: java.lang.ClassCastException: java.lang.String
StringTokenizer st = new StringTokenizer(args[0], "-");
int howMany = st.countTokens();

if (howMany == 2) {

String first = st.nextToken();
String second = st.nextToken();
String third = args[1];

Object one = first;
Object two = second;
Object three = third;

Integer temp = (Integer)map.get(one);
int num1 = temp.intValue();
Integer temp2 = (Integer)map.get(two);
int num2 = temp2.intValue();

int num3 = num2+num1;

Integer temp3 = (Integer)map.get(three);
int num4 = temp3.intValue();

Any help is appreciated
Thanks,
Jeremy

[Manfred Leonhardt]

Hi Jeremy,
I am not sure what you are doing. But the following works.

  public static void main(String[] args) 
  {
    HashMap hm = new HashMap();
    // Store some items.
    hm.put( "First", new Integer( 1 ) );
    hm.put( "Second", new Integer( 2 ) );
    hm.put( "Third", new Integer( 3 ) );
    hm.put( "Fourth", new Integer( 4 ) );
    //
    // Read two back out.
    //
    String two = "Fourth";
    String one = "First";
    Integer i1 = (Integer)hm.get( one );
    System.out.println( "First: " + i1 );
    Integer i2 = (Integer)hm.get( two );
    System.out.println( "Fourth: " + i2 );
  }

Regards,
Manfred.

[Jeremy Donaldson]

I was confused as to what element type you could populate the hashmap with. I'm assuming now that you can populate the hashmap with whatever variable you desire?
Thanks for the help.
Jeremy

[Manfred Leonhardt]

Hi Jeremy,
You can populate the HashMap with any Object you desire (not variable). I don't think it will hold primitive values.
Regards,
Manfred.

[maya pedersen]

I know this thread is some 3+ years old but my question is in the same category.
When you say you can populate Map/HashMap with any object, what exactly do you mean? I mean, I know you can put any object you want to retrieve in it but what about the key? It is also an object but doesn't this object have to be String? I've been trying to implement it with Longs (the object, not the simple type) but I can't get this to work

Please clarify, I need enlightenment

-Maya

[Ilja Preuss]

It should work with any object that implements the hashcode() method properly. It should definitely work with Long.

Can you show us some code?