Java (instanceof legality) — which two statements could be legally inserted where indicated? /* Candidate lines: 1) boolean test = (Component instanceof t); 2) boolean test = (t instanceof Ticker); 3) boolean test = t.instanceof(Ticker); 4) boolean test = (t instanceof Component); */ import java.awt.; class Ticker extends Component { public static void main (String [] args) { Ticker t = new Ticker(); / Missing Statements? */ } } Pick the pair that is syntactically valid in Java.
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A1 and 4
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B2 and 3
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C1 and 3
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D2 and 4
Answer
Correct Answer: 2 and 4
Explanation
Introduction / Context:The instanceof operator tests whether a reference refers to an instance compatible with a given type. This question focuses on syntax correctness and type positions around instanceof, not on the runtime result.
Given Data / Assumptions:
- Ticker extends Component (java.awt.Component).
- t is a Ticker instance in scope.
- We check which proposed lines compile legally.
Concept / Approach:The left operand of instanceof must be a reference expression; the right operand must be a type. The operator itself is a keyword, not a method. Supertype/superclass relationships make both t instanceof Ticker and t instanceof Component legal.
Step-by-Step Solution:
1)(Component instanceof t) → illegal: left side is a type, not an expression; right side is a variable name. Reject.2) (t instanceof Ticker) → legal: reference vs type.3) t.instanceof(Ticker) → illegal: instanceof is not a method.4) (t instanceof Component) → legal: Ticker is-a Component.Verification / Alternative check:Compiling with lines 2 and 4 produces booleans; running would yield true for both with a fresh Ticker.
Why Other Options Are Wrong:
- Options including 1 or 3 contain syntactic misuse of
instanceof.
Common Pitfalls:Attempting to put a class type on the left-hand side or treating instanceof like a method call.
Final Answer:2 and 4