[FIXED] Use java operator :: dynamically

Issue

I have the following implementation:

private SomeWritter someWritter(String someArgument) {
    SomeWritter.Builder builder = SomeWritter.builder(someArguments);
    builder = builder.addColumn("colName1", TargetClass::getArg1)
    builder = builder.addColumn("colName2", TargetClass::getArg2)
    return builder.build();
}

private Builder<T> addColumn(String colName, ToDoubleFunction<T> getter){
   //implementation goes here
}

my issue is that I need to iterate over the addColumns call, something among these lines:

private void SomeWritter(String someArgument) {
    SomeWritter.Builder builder = SomeWritter.builder(someArguments);
    for (Field field : getFilteredFieldsFromClass(TargetClass.class)) {
        builder = builder.addColumn(field.getName(), [SOMEHOW GET THE REF TO GETTER HERE])
    }
    return builder.build();
}

in order to get the refference to the getter, I tryed to do TargetClass.class.getMethod("getArg1", ...);

this works, but I have a Method, not a ToDoubleFunction.

I need to somehow get that ToDoDoubleFunction, programatically, I want to do the same that the TargetClass:: does, dinamically, not harcoded. any ideas ?

Solution

import java.lang.reflect.Field;

public class Main {
  static class Example{
    double arg1;
    int arg2;
  }
  
  interface Foo<T>{
    double toDouble(T example);
  }
  
  public static void addColumn(Foo<Example> foo){
    //do nothing
  }

  public static void main(String[] args) {
    final var example = new Example();
    
    for(Field field: Example.class.getDeclaredFields()){
      addColumn(example1 -> {
        try {
          return (double) field.get(example1);
        } catch (IllegalAccessException e) {
          throw new RuntimeException(e);
        }
      });
    }
  }
}

That code iterates over all fields of the Example class and uses the reflection inside a lambda. Side Note. Intellij can replace method references with lambda when you click alt+enter when cursor is on them (Windows).

Answered By - Alex
Answer Checked By - Candace Johnson (JavaFixing Volunteer)