CODEWITHSUNDEEP
javaoverloadingvariadic-functions
Arashsoft
Arashsoft

Reputation: 2757

Compiler error in method overloading with varags argument in Java

I have two functions like this:

String getMessage(String code, Object... objects);
String getMessage(Locale locale, String code, Object... objects);

And I try to call the first function without varags argument:

myClass.getMessage("online.order");

I get this compiler error:

Error: java: incompatible types: java.lang.String cannot be converted to java.util.Locale

It tries to use the second function and I do not understand why?

Update: Context of the code

This is the interface that define those two functions:

public interface MyMessageProvider {
    String getMessage(String code, Object... objects);
    String getMessage(Locale locale, String code, Object... objects);
}

This is the actual class that implements that interface and also extends Spring ReloadableResourceBundleMessageSource

public class CustomMessageSource extends ReloadableResourceBundleMessageSource implements MyMessageProvider {
    public static final String BEAN_NAME = "messageSource";

    public static CustomMessageSource getInstance() {
        return (CustomMessageSource) SpringApplicationContext.getBean(BEAN_NAME);
    }

    @Override
    public String getMessage(String code, Object[] objects) {
        return getMessage(getCurrentLocale(), code, objects);
    }

    @Override
    public String getMessage(Locale locale, String code, Object... objects) {
        return getMessage(code, objects, code, locale);
    }
}

And I call getMessage in a class like this:

public class MyService {
    @Autowired
    private CustomMessageSource messageSource;

    public String createSomeMessage(){
        messageSource.getMessage("online.order");
    }

}

I can solve the issue by adding String getMessage(String code) to the interface/implementation. The compile error does not makes sence to me same as you guys. But, I am getting the compile error!

Upvotes: 1

Views: 126

Answers (2)

Andrew
Andrew

Reputation: 49626

The signature of the overridden method slightly changes a parent method signature from 

public String getMessage(String code, Object... objects)

to 

public String getMessage(String code, Object[] objects)

For the compiler, it doesn't matter, it considers Object... as a thing that should be transformed to an Object[] and will make that conversion (after the compile stage is completed, there is no any Object... stuff).

Whereas for us, it does matter. We have to follow a method signature exactly. To invoke the method, you have to pass an array or null there:

instance.getMessage("code", new Object[]{});
instance.getMessage("code", null);

Upvotes: 3

Arashsoft
Arashsoft

Reputation: 2757

OMG! I found the issue myself. The issue is in the implementation class where I overrided

String getMessage(String code, Object... objects);

with

String getMessage(String code, Object[] objects)

It works fine without any issue but when I want to call getMessage without any varags argument, the override cannot handle it.

Upvotes: 0

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