How to use constructor function to add method java?

Question

I would like to add method through my constructor and use it after :

RegularAxis lon = new RegularAxis(){
    public String returnHello(){
         return "hello";
    }
};

lon.returnHello();

I cannot access my new method. is there an other way?

That's not how Java works, why do you want to do this instead of defining the method in the normal way? — UnholySheep, Aug 31 '22 at 08:05
The method has to be added in the class declaration, or via a setter which takes a function argument or something similar, like a lambda — SimonC, Aug 31 '22 at 08:05
Because my regularAxis is part of a library, I cannot edit it. And i would like a custom method — Fab83i, Aug 31 '22 at 08:06
In your example, you are creating anonymous subclass. You can: 1) use var to infer the type of the variable. Thus the `lon` variable has more precise type, giving you access to the new method. 2) Use regular subclass if you want to pass this variable somewhere, preserving its type. — Lesiak, Aug 31 '22 at 08:08
are you referring to something like [this](https://stackoverflow.com/a/1958961/16034206)? — experiment unit 1998X, Aug 31 '22 at 08:10
FYI: This is not a "constructor function" (that term doesn't exist in Java), you're creating an anonymous subclass. — Mark Rotteveel, Aug 31 '22 at 08:15

score 5 · Answer 1 · answered Aug 31 '22 at 08:06

You can call it as part of the same statement:

new RegularAxis(){
    public String returnHello(){
         return "hello";
    }
}.returnHello();

Or you can capture the anonymous type with a var variable in Java 10+ (thanks @Lesiak):

var lon = new RegularAxis(){
    public String returnHello(){
         return "hello";
    }
};

lon.returnHello();

Otherwise, you'll have to declare it as a proper class:

class IrregularAxis extends RegularAxis {
    public String returnHello(){
         return "hello";
    }
}

IrregularAxis lon = new IrregularAxis();
lon.returnHello();

How to use constructor function to add method java?

1 Answers1