Java class as a function parameter using lambda expressions

Question

I have JUnit tests (which I cannot modify) and have to write a program in Java 8. The part of the tests that I'm interested in is:

Set<Customer> mexicans = shop.filter(Customer.class, c -> c.getCountry().equals("Mexico"));
Set<Product> goldenWaffles = shop.filter(Product.class, p -> p.getBrand().equals("Golden") && p.getName().contains("Waffles"));

So the second parameter of filter function is lambda expression, which I would take as parameter of type Predicate<Product> or Predicate<Customer> (am I right here?). The problem is: I need to be able to take them both and I don't know how to do it. Has it something to do with the first parameter?

What kind of object are you trying to filter? Presumably a Customer can't be a golden waffle, and a Product can't be a Mexican; so what would it mean to apply both filters? — Dawood ibn Kareem
– Dawood ibn Kareem, Commented May 26, 2014 at 8:18
The filter method should be able to filter Customers and Products. It should probably decide what filtered set I want (Customers or Products) from the first parameter — Murkius
– Murkius, Commented May 26, 2014 at 8:34

Smutje · Accepted Answer · 2014-05-26 08:19:04Z

2

Probably you are looking for something like

public <T> void method(Class<T> clazz, Predicate<T> predicate) {
    // ...
    final Set<T> result = shop.filter(clazz, predicate);
}

answered May 26, 2014 at 8:19

Smutje

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3 Comments

Dawood ibn Kareem Over a year ago

Did you mean for this to return Set<T> instead of void?

Smutje Over a year ago

Depends on whether to work with the result of the method, or simply check for "not emptiness" or whatever.

Murkius Over a year ago

Not sure if I understand you correctly, but public Set<Product> filter(Class<Product> clazz, Predicate<Product> predicate) and public Set<Customer> filter(Class<Customer> clazz, Predicate<Customer> predicate) creates same erasure error

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