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Java Method Reference (pass method as parameter)

I want to pass method as a parameter in a method like

callMethod(someArg, methodToPass)

And in the definition of callMethod, I want to call this fn ie. MethodToPass i.e in another java file and the arguments for fn MethodToPass are being initialized in this callMethod only.

Please tell me how can I do that??

Answer*

It depends on the signature of your "methodToPass".

For example, if your method accepts a single argument and has a return type, you can use `Function<X,Y>`:

 public static <X,Y> Y callMethod (X arg, Function<X,Y> func) {
 return func.apply(arg);
 }

and call it with:

 Integer result = callMethod ("abc", String::length);

If your method has a signature that doesn't match predefined functional interfaces, you can create a custom interface.

Either generic:

 public interface MyFunc<T1,T2,T3,T4,T5>
 {
 public void apply (T1 t1, T2 t2, T3 t3, T4 t4, T5 t5);
 }

or not:

 public interface MyFunc
 {
 public void apply (Type1 t1, Type2 t2, Type3 t3, Type4 t4, Type5 t5);
 }

where TypeN represent actual classes.

Now, `callMethod` becomes (in the non-generic version):

 public static void callMethod (MyFunc method) {
 Type1 a1 = ...
 Type2 a2 = ...
 Type3 a3 = ...
 Type4 a4 = ...
 Type5 a5 = ...
 method.apply(a1,a2,a3,a4,a5);
 }

And you call it with:

 callMethod (SomeClass::methodToPass);

Where `methodToPass` is defined as:

 static void methodToPass (Type1 t1, Type2 t2, Type3 t3, Type4 t4, Type5 t5) {
 ...
 }

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My signature of "methodToPass" has return type void and it accepts 5 arguments of different types and I want to pass only its reference in "callMethod" and its arguments i'm calculating inside callMethod definition and after that I want to call this method that I passed as a Parameter with the arguments I calculated in "callMethod" fn

Shifali
– Shifali

2018年10月10日 07:51:46 +00:00
Commented Oct 10, 2018 at 7:51
Ok, I'll try this solution. I'm able to understand it and will update you about it. Thanku😃

Shifali
– Shifali

2018年10月10日 08:11:19 +00:00
Commented Oct 10, 2018 at 8:11
Useful to add that SomeClass can also be an instance if you want to call a non-static method and it can also be this if you want to reference the current instance.

Giacomo Alzetta
– Giacomo Alzetta

2018年10月10日 08:16:40 +00:00
Commented Oct 10, 2018 at 8:16

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Java Method Reference (pass method as parameter)

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