How is "(Integer)getIntent().getExtras().get(x)" different from "(Integer)getIntent().getStringExtra(x)"?

Question

I'm trying to extract an int from an Intent I created, but the second one throws up an error "Cannot convert java.lang.String to int", while the first one does not. Why does this happen?

Thanks

Answer 1

to get an int value you need to use

getIntent().getIntExtra("x", 0)

or

getIntent().getExtras().getInt("x")

Answer 2

The first one is:

(Integer)getIntent().getExtras().get(x)

This retrieves an Object based on the key x and attempts to cast that to be an Integer . If get() returns something else, you crash at runtime with a ClassCastException .

The second one is:

(Integer)getIntent().getStringExtra(x)

This retrieves a String based on the key x and attempts to cast that as an Integer . It is possible that an Object might be an Integer , which is why the first one compiles but might fail at runtime. It is not possible that a String is an Integer . Hence, this fails at compile time.

The right answer, as Mr. Oleg notes, is to call getIntExtra() on the Intent or getInt() on the Bundle returned by getExtras() .

Answer 3

It's all about casting.
getIntent().getExtras().get(x) returns an Object type.
While (Integer)getIntent().getStringExtra(x) returns an String type Object.

If you recall(or just learning), every Java Class extends Object by default and thos get it's mehtods such as toString() .
This is why you can try to cast Object to ANY class. try - but if it fails you will know it only at run-time.

On the other hand, a String is a class that already extends Object and has nothing to do with Integer and it's own values and properties.
So, when you try to cast from a String to a Integer you get an error.

The best solution was already published.
I'll just add that you can still do this:

getInteger(getIntent().getStringExtra(x));