array of arraylist and save arraylist

Programming Questions

Chrisir

array of arraylist and save arraylist

in Programming Questions • 1 year ago

Hello all,

I have two questions to arraylists

1.
Is it possible to have an array of arraylists?
I have multiple drawings each represented in an arraylist (one per page in a sketchbook) (or planning to do so).
These couple of drawings / arraylist I'd like to store in an array.
How would this beast look like? Or mission impossible?

2.
This arraylist is an arraylist of objects.
Is it possible to save the arraylist with all its objects to the hard drive? Without the saving routine knowing what's in the arraylist? This would be a universal solution. Or is there a library for that?
I could save the all the arraylists objects in a loop to text-file instead and then read it later but that sounds very slow and complicate.

The questions both are related to
http://www.openprocessing.org/visuals/?visualID=49173
and trying to develop this project further.

Thanks very much!

Greetings, Chrisir

Replies(6)

quarks

Re: array of arraylist and save arraylist

1 year ago

The solution is very dependant on the actual type of objects that are in the arraylist - you are not very clear here what it is you intend to store.

A very fast way of doing what you want is to use serialization with an arraylist of arraylists. There are a number of pros and cons to serialization.
Cons:

all the objects to be saved but be serialisable.
your object classes must implement the Serializable interface
the object class atttributes must be primative data types (e.g. int float) or other serializable class objects (e.g. String). Please be warned not all Java classes are serializeable although there is a way to overcome this limitation.
the class definifition (source code) must not be changed between the data being saved and restoredhas

Pros:

the ArrayList class is already serialisable.
to save/restore the dtat is very simple and short see below.

The following code has been taken from the G4P GUI builder tool and is used to save the tree data structure that specifies the entire GUI design. When looking at the code treeModel would be your ArrayList of ArrayLists.

public void saveModel(File file){
try {
FileOutputStream fos = new FileOutputStream(file);
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject( (CtrlSketchModel) treeModel);
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}

And to read the file

public DefaultTreeModel loadModel(File file){
DefaultTreeModel dm = null;
try {
FileInputStream fis = new FileInputStream(file);
ObjectInputStream ois = new ObjectInputStream(fis);
dm = (DefaultTreeModel) ois.readObject();
fis.close();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return dm;
}

This is just a starting point but I hope it helps.

trzewiczek

Re: array of arraylist and save arraylist

1 year ago

ad. 1
No problem in having ArrayList of arrays or array of ArrayLists. You do it normal way:

ArrayList aList = new ArrayList();

int[] ints = { 1, 2, 3, 4, 5 };
float[] floats = { 0.1, 0.2, 0.3, 0.4, 0.5 };

aList.add( ints );
aList.add( floats );

int[] intArray = (int[])aList.get(0);
for( int i = 0; i < intArray.length; ++i ) {
println( intArray[i] );
}
ArrayList[] alArray = new ArrayList[2];
alArray[0] = new ArrayList();
alArray[1] = new ArrayList<String>(); // you can specify the type if you like
alArray[0].add( 1000000 );
alArray[0].add( 3.14 );
alArray[1].add( "John" );
alArray[1].add( "Adam" );
// the rest as with usual ArrayLists

So it's no special case actually. It's all as with normal ArrayLists and normal arrays.

PhiLho

Re: array of arraylist and save arraylist

1 year ago

A library like XStream can lift a number of the limitations indicated by quarks. It can serialize to XML, to Json or even to a compact binary format. It has ways to handle old files if the objects have changed. A powerful tool.

Chrisir

Re: array of arraylist and save arraylist

1 year ago

thanks guys!

I am concentrating on trzewiczeks answer for now.

Cheers, Chrisir

Chrisir

Re: array of arraylist and save arraylist

1 year ago

@ trzewiczeks : thanks. I made an array of arrayList with the help of your answer.

@ quarks : I am trying to implement yours. But there's a lot missing. What is the File type, what is FileOutputStream and ObjectOutputStream?

I have an array of ArrayList.
In each ArrayList I store infos like PVector, String, int etc.
The purpose of each ArrayList to present a canvas with different objects. It's an drawing program like paint so the objects are Lines, boxes, spheres, texts etc.

Could you post some more of the Code showing what the types File, FileOutputStream and ObjectOutputStream are?

The questions are related to
http://www.openprocessing.org/visuals/?visualID=49173
and trying to develop this project further.

Thanks!

Greetings, Chrisir

PhiLho

Re: array of arraylist and save arraylist

1 year ago

Chrisir, search the classes in http://docs.oracle.com/javase/6/docs/api/
Search Google with "java serialization" and the class names, to find example of code.
Admittedly, this topic isn't the most simple of Java...

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