CODEWITHSUNDEEP
javainterfacedefaultdefault-method
Chamly Idunil
Chamly Idunil

Reputation: 1872

Call Method from default method in java interface

This may be silly question. but i want to know there is some possibility to do this.

Suppose I have interface like 

public interface GroupIdentifier {

    Integer getRevision();
}

And I need another method named as getNextRevision. So what i can do is, implement default method inside same interface and return next number.

EX :

public interface GroupIdentifier {

    //OUTER GET REVISION
    Integer getRevision();

    default GroupIdentifier getNextRevisionIdentifier() {
         return new GroupIdentifier() {
         //INNER GET REVISION
         public Integer getRevision() {
               //Here I want to return OUTER GET REVISION + 1
               return null;
         }
         };
    }
}

Is there some possibility to this.

Upvotes: 3

Views: 1598

Answers (4)

Marko Topolnik
Marko Topolnik

Reputation: 200168

I believe what you wanted to write is this:

public interface GroupIdentifier {
    Integer getRevision();

    default GroupIdentifier getNextRevisionIdentifier() {
        return new GroupIdentifier() {
            public Integer getRevision() {
                return GroupIdentifier.this.getRevision() + 1;
            }
        };
    }
}

You just didn't find a way to refer to the enclosing instance's getRevision(). BTW if your interface is as you've posted it, with just a single abstract method, then you can implement it much more cleanly:

public interface GroupIdentifier {
    Integer getRevision();

    default GroupIdentifier getNextRevisionIdentifier() {
        return () -> getRevision() + 1;
    }
}

Upvotes: 2

Chamly Idunil
Chamly Idunil

Reputation: 1872

I have fixed my solution as below. 

public interface GroupIdentifier {
    Integer getRevision();

    default GroupIdentifier getNextRevisionIdentifier(GroupIdentifier identifier) {
        return new GroupIdentifier() {
            @Override
            public Integer getRevision() {
                return identifier.getRevision() + 1;
            }
        };
    }
}

Upvotes: 1

Eran
Eran

Reputation: 393831

I'm not sure what's the purpose of getNextRevisionIdentifier() returning an instance of GroupIdentifier.

If you want getNextRevisionIdentifier() to return the next identifier, let it return an Integer:

public interface GroupIdentifier {

    Integer getRevision();

    default Integer getNextRevisionIdentifier() {
        return getRevision () + 1;
    }

}

Upvotes: 6

luk2302
luk2302

Reputation: 57124

Return a new instance of GroupIdentifier for which you implement getRevision accordingly:

public interface GroupIdentifier {

    //OUTER GET REVISION
    Integer getRevision();

    default GroupIdentifier getNextRevisionIdentifier() {
        //INNER GET REVISION
        Integer outer = getRevision();
        return new GroupIdentifier() {
            @Override
            public Integer getRevision() {
                return outer + 1;
            }
        }; // can be simplified to return () -> outer + 1;
    }
}

This can be run, e.g. via 

public static void main(String[] args) {
    GroupIdentifier groupIdentifier = new GroupIdentifier() {
        @Override
        public Integer getRevision() {
            return 1;
        }
    };
    System.out.println(groupIdentifier.getNextRevisionIdentifier().getRevision());
}

outputting

2

Upvotes: 2

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