Java (instanceof legality) — which two statements could be legally inserted where indicated?\n\n/* Candidate lines: \n1) boolean test = (Component instanceof t);\n2) boolean test = (t instanceof Ticker);\n3) boolean test = t.instanceof(Ticker);\n4) boolean test = (t instanceof Component);\n*/\n\nimport java.awt.;\nclass Ticker extends Component \n{\n public static void main (String [] args) \n {\n Ticker t = new Ticker();\n / Missing Statements? */\n }\n}\n\nPick the pair that is syntactically valid in Java.

Difficulty: Easy

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

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