如何在 Java 函数式代码中使用泛型

像这样试一试.您需要在方法的左侧声明类型参数，并将其包括在方法参数中.我用唱片做了演示.

只要code等字段可见，您的原始方法内容就可以很好地工作.

public class GenericMethod {
    record Fruit(int Id) {}
    record Vegetable(int Id) {}
    record Drink(int Id) {}
 
    public static void main(String[] args) {
        List<Fruit> fruits = List.of(new Fruit(20), new Fruit(30));
        List<Vegetable> vegetables = List.of(new Vegetable(100), new Vegetable(200));
        List<Drink> drinks = List.of(new Drink(2000), new Drink(3000));
      
        printObjectIds(()->fruits, Fruit::Id, "Fruits");
        printObjectIds(()->vegetables, Vegetable::Id, "Vegetables");
        printObjectIds(()->drinks, Drink::Id, "Drinks");
    }   

    static <T> void printObjectIds(Supplier<List<T>> supplier, Function<T, Integer> function, String type) {
        
        List<Integer> objectIds = supplier.get()
            .stream()
            .map(function)
            .toList();
        System.out.println(objectIds);
         
    }
}

fingerprint

[20, 30]
[100, 200]
[2000, 3000]