1Z0-829 Practice Test 14 — 15 Questions

Question 1

A class `Vehicle` has a method `start()` that returns a `String`. A subclass `Car` overrides `start()` but changes the return type to `Object`. What is the result?

Accepted Answer

Compilation fails because the return type is not covariant.. Java allows covariant return types in overriding: the subclass method may return a subtype of the original return type. Since Object is a supertype of String, changing the return type from String to Object is not covariant and is therefore a compile-time error. The override must return String or a subclass of String.

Answer

Compilation succeeds because return types are not part of the method signature.

Answer

Compilation succeeds and the method is considered an overload.

Answer

Compilation succeeds because Object is a supertype of String.

Question 2

Examine the code: List list = new ArrayList<>(); list.add("A"); list.add("B"); for (String s : list) { list.remove(s); } What is the outcome?

Accepted Answer

A ConcurrentModificationException is thrown. The for-each loop internally uses an Iterator to traverse the list. When the list is structurally modified (via `list.remove()`) during iteration without using the iterator's own `remove()` method, the iterator detects a concurrent modification and throws a `ConcurrentModificationException`. This is a fail-fast behavior of the `ArrayList` iterator.

Answer

The loop completes successfully and list becomes empty

Answer

An IllegalStateException is thrown

Answer

The loop completes successfully and list contains [B]

Question 3

A developer is reviewing a class hierarchy in which `Base` has a protected method `configure()` and a public method `start()`. Several subclasses override `configure()` and call `super.configure()` to apply base settings. Which two statements about invoking overridden methods and super are correct? (Choose two.)

Accepted Answer

A subclass can call `super.configure()` to invoke the immediate superclass version of the method, even if the method is overridden in the subclass.. The super keyword dispatches to the immediate superclass implementation, enabling subclasses to extend inherited behavior, and constructor-time calls to overridable methods dispatch to subclass overrides before subclass fields are initialized. The other statements misstate Java's rules: super chaining is unsupported, protected cross-package access is restricted to subclass-typed references, and overrides cannot narrow visibility. These distinctions matter when designing extensible base classes.

Answer

Because configure() is protected, a subclass in a different package can call it on any Base reference, not just on itself.

Answer

A subclass can use `super.super.configure()` to invoke the grandparent's implementation of configure().

Answer

Overriding configure() in a subclass with a weaker access modifier, such as private, is allowed as long as super.configure() is called.

Question 4

A developer is modeling a payment hierarchy. The abstract class Payment declares a protected abstract void process(); and a non-abstract method finalizePayment() that internally calls process(). A subclass CreditCardPayment is declared in the same package and attempts to reduce the visibility of process() when overriding it. What is the result?

Accepted Answer

The code fails to compile because an overriding method cannot reduce the access modifier of the overridden method.. When overriding a method, Java enforces that the new method must not be more restrictive than the original. Since the abstract method is protected, the override must be protected or public. Reducing to default access breaks this contract, causing a compilation failure. This rule ensures polymorphism works consistently across packages.

Answer

The code compiles and runs, but the JVM throws an IllegalAccessError at runtime when finalizePayment() invokes process().

Answer

The code compiles because the abstract method process() can be implemented with any access modifier as long as the class is concrete.

Answer

The code compiles because protected members can be overridden with default (package-private) access in the same package.

Question 5

A developer writes a method that must clean up a temporary file whether or not the processing code inside the try block succeeds. The cleanup code does not depend on any variables declared inside the try block. Which construct should the developer use to guarantee the cleanup runs in all normal exit paths?

Accepted Answer

A finally block attached to the try statement.. The finally block is designed to execute on every normal exit path from a try statement, including normal completion, return, and exception propagation. Because the cleanup does not rely on try-local variables, finally is the appropriate and idiomatic choice. Catch blocks only run on exceptions, and synchronization addresses concurrency rather than cleanup.

Answer

A synchronized block surrounding the processing code.

Answer

A catch block that catches Exception and performs the cleanup.

Answer

A catch block that catches Throwable and performs the cleanup.

Question 6

A developer needs to write a loop that prints the numbers from 1 to 10, but skips the number 5. Which loop and control statement should be used?

Accepted Answer

A for loop with an if statement and continue when the number is 5.. Using a for loop with an if condition and continue is the standard way to skip a specific iteration. The loop iterates through the range, and continue bypasses the print statement for the number 5, allowing the rest to print.

Answer

A while loop with a break statement when the number is 5.

Answer

A do-while loop with a return statement when the number is 5.

Answer

An enhanced for loop with a continue statement when the number is 5.

Question 7

A class Diagram contains a nested static class Node and an inner class Edge. A developer writes code in a static method of Diagram to create instances of both. Which statement is true?

Accepted Answer

Node can be instantiated directly, but Edge requires an instance of Diagram and cannot be instantiated from a static context without one.. Static nested classes are essentially top-level classes scoped within another class and can be instantiated without an outer instance. Inner classes are tied to an instance of the outer class. From a static context, you must create an outer instance before creating an inner class instance. This distinction is fundamental to nested class usage.

Answer

Neither Node nor Edge can be instantiated from a static method because nested classes are always private.

Answer

Both Node and Edge can be instantiated directly because they are members of Diagram.

Answer

Edge can be instantiated directly, but Node requires an instance of Diagram because it is static.

Question 8

Refer to the exhibit. The resulting image directory includes a 'bin' directory with java launcher. When running the application, a NoClassDefFoundError occurs for a class from module com.example.lib. What is the most likely cause?

Accepted Answer

The com.example.lib module was not added via --add-modules.. When using jlink to create a custom runtime image, only the modules explicitly specified (or their transitive dependencies) are included. If the application depends on com.example.lib but it was not added via --add-modules, the module's classes will be missing from the image, causing a NoClassDefFoundError at runtime. This is the most direct cause among the options.

Answer

The --compress=2 option altered the class.

Answer

The application uses reflection to access the class.

Answer

The --strip-debug option removed the class file.

Question 9

A developer defines an interface Drivable with a default method startEngine() that prints 'Engine started'. A class Car implements Drivable but also inherits a method startEngine() from its superclass Vehicle, which prints 'Vehicle engine started'. The Car class does not override startEngine(). Which method is invoked when startEngine() is called on a Car instance?

Accepted Answer

The method from Vehicle is invoked because class methods take precedence over interface default methods.. Java's method resolution follows the 'class wins' rule: if a superclass provides a concrete method, it overrides any interface default method with the same signature. This maintains compatibility with pre-existing classes. Therefore, the Vehicle implementation is used, and no explicit override is needed in Car.

Answer

The Car class must override startEngine() to call either super.startEngine() or Drivable.super.startEngine(), otherwise it will not compile.

Answer

The default method from Drivable is invoked because interfaces take precedence over superclasses.

Answer

A compile-time error occurs because the conflict between the superclass method and the interface default method must be resolved explicitly.

Question 10

A developer needs a collection that stores unique elements in the order they were inserted and allows fast O(1) membership tests. Which implementation should be used?

Accepted Answer

LinkedHashSet. The requirement is for a collection that preserves insertion order, enforces uniqueness, and provides fast membership tests. LinkedHashSet is the only standard implementation that combines these three characteristics, making it the appropriate choice for this scenario.

Answer

TreeSet

Answer

ArrayList

Answer

HashSet

Question 11

Which two of the following statements are true about the continue statement in a loop?

Accepted Answer

continue can be used in a while loop.. Option A is correct because the continue statement is valid inside a while loop, where it skips the remaining statements in the current iteration and jumps back to re-evaluate the loop condition. Option C is correct because continue also works in a for loop, causing control to jump to the loop's update expression (increment/decrement) and then re-evaluate the condition. Options B, D, and E are incorrect: continue is allowed in a do-while loop, so B is false; continue is not a switch-control statement (break is used to exit a switch), so D is false; and continue requires an enclosing loop, so using it in a try block without a loop is a compile-time error, making E false.

Answer

continue cannot be used in a do-while loop.

Answer

continue can be used in a switch statement.

Answer

continue can be used in a try block without a loop.

Question 12

A Java 17 application uses a try-with-resources block where the resource's `close()` method throws a `SQLException` and the try body throws an `IllegalStateException`. A surrounding `catch (SQLException e)` block logs the exception. Which outcome is correct?

Accepted Answer

The `IllegalStateException` propagates as primary, with the `SQLException` attached as a suppressed exception.. Try-with-resources designates the try body's exception as primary and attaches any exception from `close()` as suppressed. The `catch (SQLException e)` clause does not match the primary `IllegalStateException`, so it does not run. The `SQLException` is still available via `getSuppressed()`, which preserves diagnostic information without losing the primary failure.

Answer

The `SQLException` from `close()` is caught and logged, and the `IllegalStateException` is discarded.

Answer

Both exceptions propagate as a single `SQLException` whose cause is the `IllegalStateException`.

Answer

The JVM aborts the program because two exceptions cannot be thrown from one try-with-resources block.

Question 13

A developer is working with a Map> and needs to compute values for keys that may not be present. Which two methods from the Map interface are best suited for this task? (Choose two.)

Accepted Answer

merge. computeIfAbsent is designed for lazy initialization when a key is absent, and merge is designed for combining a new value with an existing one or inserting if absent. Both are ideal for handling maps where keys may not be present, especially when dealing with collections as values.

Answer

computeIfPresent

Answer

putIfAbsent

Answer

replaceAll

Question 14

A Java 17 method reads configuration from a `Properties` object whose keys are stored as strings. The method must parse a numeric value and throw a custom unchecked `ConfigurationException` when the key is missing or the value is not a number. Which TWO statements about writing this exception class are correct? (Choose two.)

Accepted Answer

Calling `super(message, cause)` allows the original `NumberFormatException` to be preserved for diagnostics.. A custom unchecked exception should extend `RuntimeException` so it need not appear in throws clauses, and it should pass both a message and the original cause to the superclass constructor to preserve diagnostic context. `serialVersionUID` is optional, `getMessage()` should not be overridden to delegate, and constructors should generally be public so the exception can be thrown from other packages.

Answer

The class should override `getMessage()` to return the cause's message instead of storing its own.

Answer

Constructors of an exception subclass must be declared `protected` to prevent external instantiation.

Answer

`ConfigurationException` must declare a `serialVersionUID` or it will not compile.

Question 15

A method declares a parameter of type List and receives an ArrayList. Inside the method, the developer writes list.add(42); and then Integer first = list.get(0);. Which statement describes the outcome?

Accepted Answer

The add call compiles, but the get call assigned to Integer fails to compile.. A lower-bounded wildcard permits writing Integer values because every allowed type is a supertype of Integer. Reads, however, are typed as Object since the exact element type is unknown beyond the lower bound. The add compiles, but assigning the retrieved Object to Integer without a cast does not.

Answer

The add call fails to compile because the list might be a List<Number>.

Answer

Both statements compile and run without error.

Answer

Neither statement compiles because the wildcard makes the list unusable.