Chapter 8: Lambdas and Funcional Interfaces Flashcards
Functional programming focuses more on expressions than loops.
True
Lambda expressions work with interfaces that have exactly one abstract method.
True
Parentheses around lambda parameters can be omitted if there is only one parameter and its type is not explicitly stated.
True
The lambda expression () -> true is valid and takes zero parameters.
True
A lambda expression must always have an explicit return statement.
(False, it can be omitted for single-expression lambdas.)
Lambda expressions must always declare parameter types explicitly.
(False, type inference is allowed.)
A lambda expression can have multiple abstract methods in its functional interface.
(False, only one abstract method is allowed.)
Lambdas are a feature introduced in Java 14.
(False, they were introduced in Java 8.)
The arrow operator (->) is optional in lambda expressions.
(False, it is mandatory.)
A lambda expression must always have at least one parameter.
(False, it can have zero parameters, e.g., () -> true.)
The lambda (String x) -> X.startsWith(“test”) is correct.
(False, X should be lowercase as x.)
The lambda is valid.
(String x, String y) --> x.startsWith("test")
It’s valid as long as it matches a functional interface with:
* Two String arguments
* A boolean return type
The lambda x, y -> x.startsWith(“fish”) is valid.
(False, parentheses are required for multiple parameters: (x, y) -> x.startsWith(“fish”).)
The lambda x -> { x.startsWith(“camel”); } is valid.
(False, missing return statement inside {}.)
The lambda x -> { return x.startsWith(“giraffe”) } is valid.
(False, missing semicolon inside {}.)
The lambda String x -> x.endsWith(“eagle”) is valid.
(False, missing parentheses around x.)
The lambda expression s -> {}; is invalid.
(False, it is valid as an empty lambda body.)
var invalid = (Animal a) -> a.canHop(); compiles successfully.
(False, var cannot infer the functional interface type.)
Lambdas must be enclosed within a class or method.
“Partially false. While lambdas can be assigned to a variable or passed directly as arguments, they must still be enclosed within a class or method. They cannot exist at the top level outside of a class.”
A lambda with multiple lines of code does not require braces {}.
(False, braces are required for multiple statements.)
What is an unbounded generic type in Java?
An unbounded generic type ‘<’T’>’ can accept any type, with Object as the implicit upper bound.
What is a bounded generic type in Java?
A bounded generic type
(<T extends SomeClass>)restricts T to be a subtype of SomeClass.
What does <’T extends Number’> mean?
T can be any subclass of Number (e.g., Integer, Double, Float), but not String or other non-numeric types.
What does <’T’> mean in Java generics?
It means T can be any type, effectively making it equivalent to <’T extends Object’>.
What does it enforce?
<T extends Comparable<T>>
It ensures T implements the Comparable<T> interface, allowing objects of T to be compared.
What is ‘<’T super Integer’>’ used for?
It means T can be Integer, Number, or Object—any superclass of Integer.
Can an unbounded generic type ‘<’T’>’ call methods of Number?
No, because ‘<’T> could be any type, not necessarily a Number subclass.
What is the benefit of using bounded generics?
It allows type-specific operations (e.g., T extends Number allows T.doubleValue()).
What is the difference between <’T’> and <’T’ extends ‘Object’>?
They are functionally identical, since Object is the default bound for unbounded generics.
Which generic declaration allows working with only numeric types?
’<’T’ extends Number’>’ ensures T is a number type like Integer or Double.
Why can a .java file contain a public class?
✔ A .java file can have a public class to make it accessible from anywhere in the project.
✔ The filename must match the public class name.
What happens if a .java file has a public class with a different name?
❌ Compilation error!
✔ The filename must match the public class name.
What if a .java file has no public class?
✔ The main class has default (package-private) access.
✔ The class is accessible only within the same package.
This file can be named anything (e.g., AnyName.java).
Can a .java file have multiple classes?
✔ Yes, but only one class can be public.
✔ Other classes must have default (package-private) access.
The file must be named MainClass.java.
When should a class be public vs. default?
✔ Use public when the class needs to be accessed from other packages.
✔ Use default access when the class is only for internal use within the package.
✅ Helps in encapsulation and better package organization.
What makes a lambda expression syntactically incorrect when specifying variable types?
A lambda is incorrect if it specifies variable types without enclosing the parameter list in parentheses. For example, s -> s.length() is correct, but String s -> s.length() is invalid; it should be (String s) -> s.length().
How do you correctly declare a type in a lambda expression parameter?
You must wrap the parameter in parentheses, like this: (String s) -> s.length(). Omitting the parentheses when specifying types causes a syntax error.
When can you omit parentheses in a lambda expression?
You can omit parentheses only when there’s a single untyped parameter, e.g., s -> s.length(). If the parameter has a declared type, parentheses are mandatory: (String s) -> s.length().
