将静态HashMap中的每个值转换为String Java

Question

I have got some troubles converting each value in my HashMap to a String.

    private static HashMap<String, List<Music>> musiksammlung = new 
    HashMap<String, List<Music>>(); 

This is my constructor for the HashMap. The key represents the album, the value a list of tracks from this album.
Now I want to convert each Music object to a String without creating a new HashMap, is this possible? I've tried it with the Iterator scheme, for loop over the entry set and so on but nothing seems to work.

Edit://

My code for the convertmethod:

    public HashMap<String, List<String>> generateFormatList() {
    HashMap<String, List<String>> formatList = new HashMap<String, List<String>>(); 

    for(String key : musiksammlung.keySet())
            formatList.put(key, musiksammlung.get(key).toString());  
    return musiksammlung; 

}

But this always results in an error "is not applicable for the Arguments (String, String) so I have no idea. Do I have to override toString()?

Answer 1

You're on the right path but you need to convert the existing List<Music> to a List<String> and put the List<String> into your new HashMap .

You also then want to return your newly created HashMap<String, List<String>> instead of your original one.

public HashMap<String, List<String>> generateFormatList() {
   HashMap<String, List<String>> formatList = new HashMap<String, List<String>>(); 

   for(String key : musiksammlung.keySet()) {
      // Value to store in map
      List<String> value = new ArrayList<String>();

      // Get the List<Music>
      List<Music> musicList = musiksammlung.get(key);
      for (Music m: musicList) {
          // Add String of each Music object to the List
          value.add(m.toString);
      }

      // Add the value to your new map
      formatList.put(key, value);  
   }
   // Return the new map
   return formatList;
}

So answer your question:

Now I want to convert each Music object to a String without creating a new HashMap, is this possible?

You need to create a new HashMap , because it's storing different type of value: List<Music> is different from List<String> .

Also as mentioned in my previous answer, make sure you override Music.toString() so that it returns a meaningful String for you instead of the one it inherits from its parent classes, which includes at least java.lang.Object

Answer 2

Try to change your HashMap like this:

private static HashMap<String, List<Object>> musiksammlung = new HashMap<String,List<Object>>();

So you can save any kind of objects in this HashMap . Also use instanceof to check the type of the object before using it.

Answer 3

formatList wants a List<String> , but musiksammlung.get(key).toString() returns a String (not a List<String> ). Did you mean this?

HashMap<String, String> formatList = new HashMap<String, String>();

Answer 4

Have you tried something like this:

Iterator<String> it = musiksammlung.keySet().iterator();
while (it.hasNext()) {
    List<Music> ml = musiksammlung.get(it.next());
    for (Music m : ml)
        System.out.println(m.toString());
}

And of course you should override the Music#toString() method with something you could use.