CODEWITHSUNDEEP
javaarraystype-conversion
John Smith
John Smith

Reputation: 4516

is there a universal way to work with arrays of primitives and arrays of non-primitives in java?

I understand that for every primitive type in java there is a reference type that can represent the same values, plus null. For example, int and java.lang.Integer.

I also understand that while all arrays (even java.lang.Object[]) derive from java.lang.Object, only arrays of non-primitive types can be converted to java.lang.Object[].

In other words, we can do:

Class type = Integer.class;
Object[] o = (Object[])java.lang.reflect.Array.newInstance(type, 4);

but the following results in an exception:

Class type = int.class;
Object[] o = (Object[])java.lang.reflect.Array.newInstance(type, 4);

so in that particular case we could do:

 Class type = int.class;
 Object o = java.lang.reflect.Array.newInstance(type, 4);

...which seems fine, until one wonders how to add elements to an Object that represents an array that cannot be converted to Object[].

is the only way around this problem to check the type of the elements of the array and cast the Object as appropriate?

ie:

  if (type == int.class)
  ((int[])o)[0] = getFirstElement();

  else if (type == short.class)
  ((short[])o[0] = getFirstElement();

Upvotes: 2

Views: 309

Answers (2)

matts
matts

Reputation: 6897

Besides creating arrays, java.lang.reflect.Array also offers methods to get and set elements in arrays:

Class<?> type = int.class;
Object array = java.lang.reflect.Array.newInstance(type, 4);

int index = 0;
Object value = getFirstElement();
java.lang.reflect.Array.set(array, index, value);

Also note from the documentation that the value is first automatically unwrapped if the array has a primitive component type. So this should work for any array, including those that do not inherit from Object[].

There is a corresponding Object get(Object array, int index) method too.

Upvotes: 1

Hot Licks
Hot Licks

Reputation: 47729

Well, in the first case you can assign to Object and then use isInstanceOf Object[] to see if you have an array of Object.

But ultimately you have to have some sort of conditional operation to do element access/assignment. Thankfully there are only (IIRC) 7 different scalar data types.

(The language spec could have defined the Integer/Float/et al to include array member access methods -- eg, Integer would define get and set methods for int[]. But they didn't. At best you could define wrappers for the (alas, final) Number subclasses to define these methods.)

Upvotes: 1

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