D286 Java Fundamentals - Set 5 - Part 1

Correct Answer: Result: 34

Evaluation proceeds left to right. "Result: " + 3 produces "Result: 3", then + 4 concatenates again, giving "Result: 34".

Correct Answer: Result: 7

Parentheses force the numeric addition first, producing 7, which is then concatenated to give "Result: 7".

Correct Answer: 3

The body runs with i equal to 0, 1, and 2, incrementing each time. When i reaches 3 the condition fails, giving 3 executions.

Correct Answer: 321

The loop counts down from 3 to 1, printing each value without a newline, producing 321.

Correct Answer: 3

The array literal creates three elements, so the length field returns 3. Valid indices are 0 through 2.

Correct Answer: It avoids creating 1000 intermediate String objects

String concatenation creates a new immutable String each iteration. StringBuilder mutates one internal buffer, dramatically reducing object creation and time.

Correct Answer: String literals are interned and may share the same object

Java interns String literals in a pool, so identical literals reference the same object. This is why == can appear to work for literals but fails for new String().

Correct Answer: true, because small Integers are cached

Java caches Integer objects between -128 and 127, so autoboxed values in that range reference the same object. Beyond that range == would return false.

Correct Answer: == compares references, which is unreliable outside the cache range

Because == compares object identity, wrapper comparisons succeed only within the cached range. equals() reliably compares the underlying values.

Correct Answer: Copying a mutable object before storing or returning it to protect internal state

Defensive copying prevents callers from holding a reference to internal mutable state, which they could otherwise modify and break the object's invariants.

Correct Answer: They must implement AutoCloseable

Resources declared in try-with-resources must implement AutoCloseable so the compiler can generate the automatic close() call.

Correct Answer: Let it propagate or wrap it with context and rethrow

Swallowing exceptions hides failures. Propagating or wrapping with additional context lets a level capable of handling it respond appropriately.

Correct Answer: It hides unexpected errors and makes diagnosis harder

Catching the broad Exception type captures problems you did not anticipate, potentially masking serious bugs and making failures difficult to diagnose.

Correct Answer: Recording runtime events for diagnosis and monitoring

Logging records events, errors, and state during execution, providing the diagnostic trail needed to understand behavior and troubleshoot production problems.

Correct Answer: Passwords, tokens, and other sensitive credentials

Logs are widely accessible and often retained long-term, so credentials and sensitive personal data must never be written to them.

Correct Answer: Controlling which code may read or modify the field

Access modifiers enforce encapsulation by restricting which code can reach a field, protecting invariants and allowing internal representation to change.

Correct Answer: Any code can change them, breaking encapsulation and invariants

Public mutable fields let arbitrary code modify state without validation, breaking invariants and making the class impossible to change safely later.

Correct Answer: A class should have one reason to change

The Single Responsibility Principle states a class should have one well-defined responsibility, so only one kind of requirement change forces it to be modified.

Correct Answer: It becomes hard to understand, test, and change safely

Classes accumulating many responsibilities become difficult to reason about, and changes for one concern risk breaking unrelated behavior in the same class.

Correct Answer: The degree to which one component depends on another

Coupling measures interdependence between components. Loose coupling is preferred because it allows components to change independently.