Why not use Object for all method parameters?

Question

public class helloworld {
    public static void main(String[] args) {
        String text = "Hello World";
        l(text);
        int n = 0;
        l("--------------------------");
        l(n);   
    }

    public static void l(Object obj) {
        System.out.println(obj);
    }
}

I wrote this simple program in Java and it worked. Now I am confused that if all the data types (int, char, double etc.) come under Object, then why do we specify which data type we want to accept when we pass values?

I mean we can always use the data type Object as used in the function l. Is there a specific reason why people don't always use Object as their data type to pass values?

Answer 1

There is an implicit conversion defined between all primitive types and their respective object counterparts:

int -> Integer
char -> Character
etc...

This is called autoboxing.

Is there a specific reason why people don't always use "Object" as their data type to pass values?

Since Java is strongly typed, you cannot do a whole lot with Object.

E.g. try this:

static Object add(Object a, Object b) {
    return a + b; // won't compile
}

This is because methods, operators, etc. available to use depend on the static type of the variable.

println can accept Object because it only needs to call the toString method. If you only need the limited functionality provided by the methods in Object, then sure, you can use it as a type. This is rarely the case, however.

Answer 2

For the primitives you mentioned, they are not really objects, they will simply be boxed to their representation as an object. An int would become an Integer, a long would become a Long etc.

Read this article about Autoboxing in java.

As for your question

Is there a specific reason why people don't always use "Object" as their data type to pass values?

If you specify Object as the parameter of your method you won't be able to call the methods the real object contains without doing a cast. For example, if you have a custom object AnyObject that contains a method anyMethod, you won't be able to call it without casting the object to AnyObject.

It will also be unsafe as you will be able to pass any type of object to a method which may not be designed to function properly with any of these types. A method containing only System.out.println is not representative of a real use case, it will work with any object simply because by default the println will call the toString method which is already defined in an Object.

Answer 3

While it does look like a function that appears to accept all types of parameters, you will have to deal with these

• The function signature becomes less informative.
• No more overloading
• You have to do a lot of type checking and casting in the function body to avoid run time errors.
• Although the method seemingly accepts all objects, you would never know the actual subset of them until you see the method definition.
• The function body might end up having more code to eliminate the wrong types than for its real goal. For example, your function only prints the value. Imagine a function that predominantly does some integer operation.
• Increases the probability of run time errors, as the compiler cannot throw errors for missing casts.