I found the following source code in gson:
public <T> T fromJson(Reader json, Type typeOfT) throws JsonIOException, JsonSyntaxException
{
JsonReader jsonReader = newJsonReader(json);
T object = (T) fromJson(jsonReader, typeOfT);
assertFullConsumption(object, jsonReader);
return object;
}
Does it matter if fromJson function declares to return an Object or return T? at least from my knowledge, if the T can not be inferred by function arguments it acts exactly as object. So why the source code uses T instead of an Object?
This doesn't return Object but a type that's either inferred from the context or – if that's not possible – by passing a type parameter with a type witness: YourClass.<String>fromJson()
Note that this won't magically work. If the object that's returned from the internal call isn't compatible with T at runtime, the assignment (of the outer return value) will throw a ClassCastException.
Example:
public class MyClass {
public static void main(String args[]) {
String result1 = MyClass.test(); // works as expected
Object result2 = MyClass.<Integer>test(); // works "surprisingly"
int result3 = MyClass.test(); // cannot be cast to java.lang.Integer
}
static <T> T test() {
try {
return (T) "Hello World";
} catch (ClassCastException e) {
throw new Error(); // never reached
}
}
}
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