Java：序列化未知的Arraysize

Question

If I safe an Array and reload it, is there a possibility to get the size if its unknown? Thanks

Answer 1

What do you mean by "unknown"? You can get the length of any java array with the length field.

int[] myArray = deserializeSomeArray();
int size = myArray.length;

Answer 2

It sounds like you're serializing and storing the individual objects in the array (after much reading between the lines). Use the ObjectOutputStream to store the array itself. If the objects stored in the array are serializable, they'll be stored too. When you deserialize you'll get the entire array back intact.

Answer 3

I think you need to supply some more information. How are you saving the array? Using an ObjectOutputStream?

Answer 4

否，因为数组的长度仅是分配的内存大小除以存储在其中的对象的大小，并且由于没有对象的大小为0，因此您将始终具有适当的长度（可以为0）

Answer 5

如果使用ObjectInputStream.readObject（）读取保存的数组，则将使用适当的长度对其进行重构，并且可以使用array.length读取大小。

Answer 6

Attempting to read between the lines...

If you are actually reading array, then (unlike C) all arrays know their length. Java is a safe language, so the length is necessary for bounds checking.

MyType[] things = (MyType[])in.readObject();
int len = things.length;

Perhaps your difficulty is that you are doing custom (de)serialisation and are writing out individual elements of the array (hint: don't - use an array). In the case you need to catch OptionDataException to detect the end of the enclosing object's custom data:

private static final MyType[] NOTHING = new MyType[0];

private transient MyType[] things = NOTHING;

private void writeObject(ObjectOutputStream out) throws IOException {
    out.defaultWriteObject(); // Do not forget this call!
    for (MyType thing : things) {
        out.writeObject(thing);
    }
}
private void readObject(
    ObjectInputStream in
) throws IOException, ClassNotFoundException {
    in.defaultReadObject(); // Do not forget this call!
    List<MyType> things = new ArrayList<MyType>();
    try {
        for (;;) {
            things.add((MyType)in.readObject();
        }
    } catch (OptionalDataException exc) {
        // Okay - end of custom data.
    }
    this.things = things.toArray(NOTHING);
}

If you are going to do that sort of thing, it's much better to write out the number of objects you are going to read as an int before the actual data.