Immutable Type: public final fields vs. getter

Question

I need a small Container-Class for storing some Strings which should be immutable. As String itself is an immutable type, I thought of something like that:

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Answer 1

Using public final may be fine for such small job, but it cannot be adapted as a standard practice,

Consider the situation below.

Public class Portfolio {
   public final String[] stocks;
}

Of course, being immutable, this object is initialized vis constructor, and then accessed directly. Do I have to tell you the problem in it? It’s evident!

Consider your client writing the code like below -

Portfolio portfolio = PortfolioManager.get(“Anand”);
Portfolio.stocks[0] = “FB”;
portfolio.calculate();

Is this doable? Your client libraries are able to manipulate the state of your objects, or rather able to hack within your runtime representation. This is a huge security risk, and of course tools like SONAR catch it upfront. But its manageable only if you are using getter-setters.

If you are using getters, you can very well write

   Public class Portfolio {
      private final String[] stocks;
      public String[] getStocks() {
          return Arrays.coptOf(this.stocks);
      }
   }

This prevents you from potential security threat.

Looking at the above example, using public final is strongly discouraged if you are using arrays. In such case, it cannot become a standard. A person like me, will refrain from using a code practice that cannot become a uniform standard across all data types. What about you?