Practice Test Geeks(1Z0-819) Oracle Java SE 11 Developer Practice Test
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Generics & Type Inference Flashcards

7 cards from real 1Z0-819 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is the var keyword available in Java 10 and Java 11?

    Answer: A keyword for local variable type inference that lets the compiler determine the type

    var is a reserved type name for local variable type inference; the compiler determines the variable's type from the right-hand side initializer expression at compile time.

  2. Which of the following var declarations is INVALID in Java 11?

    Answer: var x;

    var requires an initializer expression so the compiler can infer the type; declaring var x; without an initializer is not allowed because the type cannot be determined.

  3. Where can the var keyword NOT be used in Java 11?

    Answer: As the declared type of an instance field in a class

    var can only be used for local variable type inference; it cannot be used for instance fields, static fields, method parameters, or method return types.

  4. Why can you NOT instantiate a generic type parameter with new T() in Java?

    Answer: Due to type erasure, T is not available at runtime so the JVM cannot know which class to instantiate

    Because of type erasure, T is erased to Object (or its upper bound) in bytecode, so the JVM has no information about the actual class T represents when new T() would be executed.

  5. Which of the following correctly relies on type inference for a generic method call?

    Answer: List list = Collections.emptyList();

    The compiler infers the type argument for Collections.emptyList() from the target type List on the left-hand side, so no explicit type witness is needed.

  6. At runtime, how can you check if an object is specifically a List?

    Answer: You cannot check for the parameterized type at runtime due to type erasure

    Due to type erasure, generic type parameters are not available at runtime, making instanceof List a compile error; you can only check instanceof List.

  7. What is the inferred type of the variable 'map' in: var map = new HashMap>();?

    Answer: HashMap>

    var infers the exact static type of the right-hand side expression, which is HashMap> — the concrete class, not the Map interface.