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i'm new to android and i'ld like to understand how i can save an array to memory. I don't mean internal memory, as i know about shared preferences, external storage and sqlite. I'm looking at something within the range of RAM/Heap.

The actual challenge is that i have a string array of names. I get the names from an sqlite database when app is first started.

e.g 

String[] names = new String[] {"dave", "james", "tommy" }

This list can grow to contain over 10000 items.

In another activity, i want to check if some names exist in the list. I don't want to query the database back and forth to achieve this. That is why i'm thinking that saving in memory may just be the best bet as it can improve performance.

So i'ld like to know how to save this array in memory and read from it in another activity. I already know how to manage my RAM i'm just looking for ways to get this info there and read from it.

Thanks

OneCricketeer
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Tajinere
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  • this list is static or can be changed ? – Youcef LAIDANI Mar 11 '17 at 16:50
  • i mean can the values changes or not @Os. – Youcef LAIDANI Mar 11 '17 at 16:52
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    Your list is already in RAM / heap. It's a Java object... – OneCricketeer Mar 11 '17 at 16:56
  • A SQL query of `SELECT name FROM names WHERE name LIKE "othername"` is a really cheap SQL operation, so why not do that? – OneCricketeer Mar 11 '17 at 16:57
  • "This list can grow to contain over 10000 items" it's not a list, it's an array; and arrays can't grow. Use an `ArrayList` instead if you want to be able to "grow" the list. – Andy Turner Mar 11 '17 at 17:49
  • @AndyTurner sorry bout that, must have been the context. I just meant that the list copied into the array can expand. – Tajinere Mar 11 '17 at 18:06
  • Best bet is to use share preferences. Then use gson to serialize the data into a string json structure. If you just sending across activities use parceble interface for serialization. This link is excellent. https://developer.android.com/training/basics/data-storage/shared-preferences.html For Gson a quick starter http://howtodoinjava.com/best-practices/google-gson-tutorial-convert-java-object-to-from-json/ For parcelable http://www.survivingwithandroid.com/2015/05/android-parcelable-tutorial-list-class-2.html Happy reading! – Remario Mar 11 '17 at 16:53

1 Answers1

2

Create a Singleton Pattern and put your array into it and you can share your array across your app instance but remember this singleton class will be destroyed with the app so will your you array inside it.

This is how a singleton is created.

class Bar {
private static class ArrayHolder {
    public static List<String> array = new ArrayList<>();
}

public static Bar getArray() {
    return array;
}
}

Whenever you need to access your array just do this ArrayHolder.getArray()

Community
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Rahul Kumar
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  • What's the purpose of the `ArrayHolder` class here? It looks like you're trying to do the lazy holder idiom, incorrectly; but the laziness looks unnecessary. – Andy Turner Mar 11 '17 at 17:50
  • can i get the data from the array in another activity using the singleton approach? – Tajinere Mar 11 '17 at 17:52