How to correctly use HashMap?

Question

HashMap savedStuff = new HashMap();
savedStuff.put(\"symbol\", this.symbol); //this is a string
savedStuff.put(\"index\", this.index); //this is an int

Answer 1

I'm not sure what you're trying to do, but since the example you provided uses hard-coded strings to index the data, it seems like you know what data you want to group together. If that's the case, then a Map is probably not a good choice. The better approach would be to make a class out of the commonly grouped data:

public class SavedStuff {
  private int index;
  private String symbol;

  public SavedStuff(int index, String symbol) {
    this.index = index;
    this.symbol = symbol;
  }

  public int getIndex() {
    return index;
  }

  public String getSymbol() {
    return symbol;
  }
}

This allows your client code to do this:

SavedStuff savedStuff = ...
String symbol = savedStuff.getSymbol();

Rather than this:

Map savedStuff = ...
String symbol = savedStuff.get("symbol");

The former example is much less fragile because you're not indexing data with String constants. It also gives you a place to add behavior on top of your grouped data, which makes your code much more object oriented.