Given: public class Product { String name; int qty; public String toString() { return name; } public Product(String name, int qty) { this.name = name; this.qty = qty; } static class ProductFilter {…

Question

Options

• AImplement Predicate in the Product.ProductFilter class and replace line n2 with .filter (p -> p.ProductFilter.test (p))
• BReplace line n1 with: public static boolean isAvailable (Product p) { return p.qty >= 10; } Replace line n2 with: .filter (p -> p.ProductFilter.isAvailable (p))
• CReplace line n2 with: .filter (p -> Product::isAvailable)
• DReplace line n2 with: .filter (p -> Product::ProductFilter::isAvailable ())

• A
  7% (4)
• B
  78% (45)
• C
  12% (7)
• D
  3% (2)

Explanation

Option B works because making isAvailable static allows it to be called directly on the ProductFilter class without needing an instance - the lambda p -> Product.ProductFilter.isAvailable(p) correctly passes each stream element into the static method, which returns true for qty ≥ 10, so only "Speaker" (qty=20) passes through.

Why the others fail:

• A is wrong because p.ProductFilter is not a valid expression - ProductFilter is a class name, not a field on a Product instance, so you cannot obtain a Predicate instance this way.
• C is wrong because p -> Product::isAvailable is invalid syntax - you cannot use a method reference as the body of a lambda that must return a boolean; also, isAvailable doesn't exist directly on Product.
• D is wrong because chaining :: operators (Product::ProductFilter::isAvailable()) is not legal Java syntax - there is no double-colon chaining in method references.

Memory tip: For filter() to accept a method reference or lambda, the expression must evaluate to a boolean. If the method lives in a static nested class, make it static so you can call it as OuterClass.InnerClass.method(element) inside a lambda - no instance of the nested class required.

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