LinkedHashSet does not main insertion order?

Question

I am currently building an Android app where I display quotes from famous people. I have a home screen and 2 other screens, where I am displaying all quotes and the other where I display favourite quotes.

So, when I hit the like button in the screen of AllQuotesActivity the quote and author will be saved in a LinkedHashSet, which will be saved in SharedPreferences, so my FavouriteQuotes Activity can obtain the data. I can obtain the data, but the data is mixed, even though other links say that LinkedHashSet maintains the insertion order. Maybe I did something wrong. Here are the important code snippets:

AllQuotesActivity.java:

SharedPreferences sharedPref;
Set<String> set = new LinkedHashSet();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.all_quotes);

    Resources res = getResources();
    Context context = getApplicationContext();
    this.sharedPref = context.getSharedPreferences(
            "MyPref", Context.MODE_PRIVATE);
    final String[] quotesAndAuthors = res.getStringArray(R.array.quotes);

    button3.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            set.add(quotesAndAuthors[counter]);
            set.add(quotesAndAuthors[counter + 1]);
        }
    });

}

@Override
public void onPause() {
    super.onPause();
    Log.d("RichQuotes", "Its paused mkay");

    Editor editor = sharedPref.edit();

    editor.putStringSet("quotesAndAuthors", this.set);
    editor.commit();
}

}

FavouriteQuotesActivity.java:

SharedPreferences sharedPref;
Set<String> set = new LinkedHashSet();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.favourite_quotes);

    Resources res = getResources();
    Context context = getApplicationContext();
    this.sharedPref = context.getSharedPreferences(
            "MyPref", Context.MODE_PRIVATE);

    set = sharedPref.getStringSet("quotesAndAuthors", null);

    for (Iterator<String> it = set.iterator(); it.hasNext(); ) {
        String s = it.next();
        Log.v("test", s);
    }

I removed unnecessary code.

In the FavouriteQuotesActivity.java I am logging the set to check its values. The log-outputs and the outputs on the screen are the same, both unsorted the same way.

It would be helpful if you could reduce this to a simple block of code, that instantiates a linked hash set, adds some data, and iterates over the set — David, Jan 18 '20 at 15:29
This is probably unsupported. My guess is, the return value from `getStringSet()` is not a `LinkedHashSet`. — greeble31, Jan 18 '20 at 17:01

Basil Bourque · Accepted Answer · 2020-01-18T18:05:53.317

0

Set set = new LinkedHashSet();

In this line, you instantiate a new empty LinkedHashSet object. This object was then assigned to the variable named set.

set = sharedPref.getStringSet("quotesAndAuthors", null);

In this line, you reassigned the set variable to point to some other object, some Set object returned by your call to getStringSet. We do not know the concrete class of this second object that implements the Set interface. You can ask by calling getClass.

Your first set, the empty LinkedHashSet, went unused. With no other references pointing to it, that set became a candidate for eventual garbage-collection.

edited Jan 18 '20 at 18:05

answered Jan 18 '20 at 17:40

Basil Bourque

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Thanks for pointing that out. I changed to set.addAll and added the StringSet. However the problem is "getStringSet()" cause it mixes the values from the LinkedHashSet. Any ideas how to overcome this? – Jan 19 '20 at 11:35

LinkedHashSet does not main insertion order?

1 Answers1