Storing arbitrary primitive types in an a java array

Question

I have a use case where I must parse JSON into primitive values in Java. I have instructive fields embedded in the JSON that informs my parsing which primitive to deserialize to. These primitive types must be added to an array of some length.

So I may have some JSON like this:

"primitives" : [
{
"valueType" : "int",
"value" : 3
},
{
"valueType" : "double",
"value" : 4
},
]

I have written the code to properly parse this JSON into two primitives, one int and double with values 3 and 4. However, because I am adding them to an ArrayList which expects Objects they are autoboxed into Java's Integer and Double types. I thought of using a regular Java Array but there is still the problem of specifying the element type like Object[] arr where I have the same problem, or int[] where I am being too specific.

Is there some functionality within Java that can allow me to parse this JSON to the correct Array of primitives.

One solution I have considered is an object that has all the different primitives as properties but this seems like too much complexity if a language level path is available.

How are you going to retrieve the values, since it seems like you would need to know the specific type? For example, int value1 = SomeArray[0], and double value2 = SomeArray[1] seems like you would need to know the type of the value. — KevinO
– KevinO, Commented Apr 8, 2016 at 3:58
Why don't you just use Jackson or an alternative JSON parser? You're reinventing the wheel and adding redundant type info to your JSON. — elhefe
– elhefe, Commented Apr 8, 2016 at 4:06

KevinO · Accepted Answer · 2016-04-08 04:18:11Z

2

Assuming that it is important to keep the original ordering (thus a single array), and that keeping track of the type is important, and that using a JSON parser is unavailable, I would consider something like the following.

enum ValueType { INT, DOUBLE, FLOAT };

static abstract class ParsedValue<T>
{
    private final T data;
    private final ValueType type;

    public ParsedValue(T val, ValueType t)
    {
        data = val;
        type = t;
    }

    public ValueType getType()
    {
        return type;
    }

    public T getValue()
    {
        return data;
    }
}

static class IntParsedValue extends ParsedValue<Integer>
{
    public IntParsedValue(Integer val)
    {
        super(val, ValueType.INT);
    }
}

static class DoubleParsedValue extends ParsedValue<Double>
{
    public DoubleParsedValue(Double val)
    {
        super(val, ValueType.DOUBLE);
    }
}


public static void main(String[] args)
{
    List<ParsedValue<?>> lst = new ArrayList<>();

    Random rnd = new Random();

    for (int i = 0; i < 25; ++i) {
        ParsedValue<?> pv;            
        if (rnd.nextInt(2) == 0) {
            pv = new IntParsedValue(rnd.nextInt(500));
        }
        else {
            pv = new DoubleParsedValue(rnd.nextDouble());
        }

        lst.add(pv);
    }

    for (ParsedValue<?> pv : lst) {
        switch (pv.getType()) {
        case INT:
            System.out.println("Integer: " + pv.getValue());
            break;

        case DOUBLE:
            System.out.println("Double: " + pv.getValue());
            break;

        case FLOAT:
            //...
            break;
        }


    }

}

answered Apr 8, 2016 at 4:18

KevinO

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1 Comment

Alex Bollbach Over a year ago

So you basically expanded on the idea I suggested at the end of my question. Thank you for the help, I will most likely incorporate this into my approach. The subclasses setting an enum is a nice touch I might not have thought of so I appreciate this answer.

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