Android java method - Can a parameter be more than one type?

Question

I'm new to java/android and would really appreciate help with this. I would like my java method to be able to take in more than one type for the parameter. For example the variable myButton could be an ImageButton or just a Button. The code inside myFunction is valid for whether myButton is an ImageButton or a Button.

if (condition) {
    ImageButton myButton = (ImageButton) findViewById(R.id.myButtonID);
    myFunction(myButton);
} else {
    Button myButton = (Button) findViewById(R.id.myButtonID);
    myFunction(myButton);
}

public void myFunction(Button or ImageButton myButton) {
    ....identical code for myButton which could be an ImageButton or Button....
}

I could obviously write out 2 funcions for parameter type and call it when applicable but that seems like a waste and there must be a quicker way. How can I do this? Thanks for your help.

Generics? http://docs.oracle.com/javase/tutorial/java/generics/types.html. and this http://stackoverflow.com/questions/16131410/implementing-methods-from-an-interface-but-with-different-parameters — Raghunandan, Dec 31 '13 at 08:15
Sounds like inheritance is the solution here. Declare the function parameter as a common supertype. — Henry, Dec 31 '13 at 08:19

score 5 · Answer 1 · answered Dec 31 '13 at 08:14

5

If both classes have a common interface that can be used inside your method, you can use it and catch both types.

Otherwise, you can use overloading or generic method.

answered Dec 31 '13 at 08:14

BobTheBuilder

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laalto · Answer 2 · 2013-12-31T08:39:53.050

Depends on what the method does to the passed in parameter.

Usually, you'd use polymorphism. Looking at the inheritance graphs,

ImageButton extends ImageView extends View extends Object

and

Button extends TextView extends View extends Object

The most specific common superclass is View. If the method can work on Views, then you should specify the parameter type to be a View:

public void myFunction(View view) {
    //...
}

If the method does different things to ImageButtons and Buttons, then you can use method overloading. That is, two methods that have take different parameters:

public void myFunction(ImageButton imageButton) {
    //...
}

public void myFunction(Button button) {
    //...
}

In rare cases, a generics-based solution could also work. Note that the compiler will actually generate copies of the code for each different type passed in, so you should prefer polymorphism-based solution when you can:

public <ParamType extends View> void myFunction(ParamType param) {
    //...
}

score 0 · Answer 3 · answered Dec 31 '13 at 08:23

0

You should use common super class of the Button and ImageButton which is for example View and then:

public void myFunction(View view) {
    if(view instanceof Button) {
        Button btn = (Button) view;
        // do something with Button instance
    }

    if(view instanceof ImageButton) {
        ImageButton iBtn = (ImageButton) view;
        // do something with Image Button instance
    }
}

answered Dec 31 '13 at 08:23

piobab

1,352
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Needing to resort to reflection (`instanceof`) is usually a code smell indicative of design problems. – laalto Dec 31 '13 at 08:25
The same thing is being done to Button and ImageButton...so the same code would be repeated twice which is kinda inefficient – pauloz1890 Dec 31 '13 at 08:26
I agree with laalto about reflection. It will be easier to find optimal solution with source code provided. – piobab Dec 31 '13 at 08:33

Android java method - Can a parameter be more than one type?

3 Answers3