1Z0-811 Practice Test 32 — 15 Questions

Question 1

A developer designs a class named BankAccount that stores a private field accountNumber. The field must never be modified after the constructor runs, and other classes must be able to read its value. Which declaration best satisfies these requirements?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

private final String accountNumber;. Marking the field private final keeps it hidden from other classes and allows a single assignment, typically inside the constructor. A public getter can then return the value for reading without exposing a setter. Public or protected fields allow later modification, and a static field would incorrectly share one value across all instances.

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protected String accountNumber;

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private static String accountNumber;

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public String accountNumber;

Question 2

A developer writes a method that may throw a checked exception and wants to document the exception for callers. Which two statements about the `throws` clause are correct? (Choose two.)

Accepted Answer

A method can declare multiple checked exceptions in its throws clause, separated by commas.. The throws clause lists checked exceptions that a method might propagate to its caller, and it may contain several types separated by commas. Declaring an exception does not force the method to throw it, because the clause defines a caller-facing contract. Overriding methods, however, may only narrow the checked exceptions declared by the overridden method, never add new ones.

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A throws clause must list every exception that the method body can possibly throw, including unchecked ones.

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A method that overrides a superclass method may declare additional checked exceptions not declared by the overridden method.

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Only unchecked exceptions can appear in a throws clause.

Question 3

A developer is writing a method that catches multiple exception types in a single catch block using the multi-catch feature. The catch clause is: catch (IOException | SQLException e) { ... }. Which statement is true about the variable e in this catch block?

Accepted Answer

The variable e is implicitly final and cannot be reassigned within the catch block.. In a multi-catch clause, the exception parameter is implicitly final. This means it cannot be reassigned within the catch block. This restriction is enforced by the compiler to maintain type safety and to allow the compiler to generate efficient bytecode. The variable's type is the least upper bound of the caught types, and only methods available on that type can be called.

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The variable e is of type Exception, so you can call any method defined in Exception.

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The variable e can be used to rethrow the exception, but only if the method declares throws for both IOException and SQLException.

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The variable e can be reassigned to a new exception object of any type.

Question 4

A developer is writing a method that must accept a two-dimensional array of int values and compute the sum of all elements. The array is declared as int[][] grid. The array may be ragged, meaning rows can have different lengths. Which two statements are correct about iterating over grid to compute the total? (Choose two.)

Accepted Answer

A nested for-each loop such as for (int[] row : grid) for (int value : row) sum += value; works correctly for ragged arrays.. A 2D array in Java is an array of arrays, so each row can have its own length. Nested indexed loops that use grid.length and grid[i].length, or nested for-each loops over rows and then elements, correctly traverse ragged data. Assuming a fixed column count from grid[0].length or treating grid.length as the total element count produces wrong bounds and potential exceptions.

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The expression grid.length returns the total number of int elements in the 2D array, not the number of rows.

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A single for-each loop over grid, such as for (int value : grid), compiles and sums all elements correctly.

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Using grid[0].length as the column bound for every row is safe because all rows in a 2D array must have the same length.

Question 5

A method declares `public void parse(String input) throws IOException`. Inside the method body, the code calls another method that declares `throws IOException` but does not throw it in every execution path. A reviewer asks the developer to document the method contract without changing behavior. Which statement best describes the effect of the `throws IOException` clause in the method signature?

Accepted Answer

It forces every caller of `parse` to handle or declare `IOException`, regardless of whether an exception is actually thrown at runtime.. The `throws` clause is a compile-time declaration that a method may propagate a checked exception. It obligates callers to catch or declare that exception, but it does not force the exception to occur at runtime. The declaration documents the method contract and is enforced by the compiler, not by runtime checks.

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It guarantees that `parse` will throw `IOException` at least once during every execution.

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It converts `IOException` into an unchecked exception for callers of `parse`.

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It allows callers to ignore `IOException` because the method declares it explicitly.

Question 6

A developer defines an interface `Printable` with a single method `void print()`. A class `Report` implements `Printable` but declares the method as `public void print() throws IOException`. The developer compiles the code and receives a compiler error. What is the reason?

Accepted Answer

An implementing method may not declare a broader checked exception than the interface method declares.. The overriding and implementing rule restricts a method from declaring broader checked exceptions than the method it implements or overrides. Because Printable.print() declares no checked exceptions, adding IOException expands the contract in a way callers of the interface cannot anticipate, so the compiler rejects it. Unchecked exceptions remain freely permitted in the implementing method.

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Interface methods are implicitly final, so the implementing class cannot change the method signature at all.

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The class Report must be declared abstract before it can implement any interface method that throws an exception.

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The implementing method must be declared abstract when it throws a checked exception.

Question 7

A developer is designing a Java application with an interface `Vehicle` and several implementing classes. Which two statements about interface implementation are correct? (Choose two.)

Accepted Answer

A class that implements an interface must provide implementations for all of the interface's abstract methods unless the class is declared abstract.. Interfaces support multiple implementation, and a concrete implementing class must satisfy every abstract method inherited from all listed interfaces or be declared abstract. These two rules work together: the implements clause can name several interfaces, and the compiler enforces completeness so that any instantiated object fully honors every contract it claims to support.

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A class can extend at most one class but cannot implement any interface at the same time.

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An interface can be instantiated directly using the new keyword as long as all its methods are implemented.

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An implementing class must declare its overridden interface methods with the private access modifier.

Question 8

A developer writes a method that prints a message and then returns early when a validation check fails. The method signature is public void process(int value). Inside the method, the developer writes: if (value < 0) { return; } System.out.println(value); The code compiles and runs. Which statement best explains why the bare return statement is valid here?

Accepted Answer

The return statement is valid because void methods may use return to exit the method early without a value.. A method declared with the void return type may use a value-less return statement to terminate early, which is exactly what the guard clause does when the validation fails. Because no value is expected, the compiler permits the bare return, and the following println is skipped. Control simply returns to the caller without any result being produced.

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The return statement is valid because Java automatically converts the void method into an int-returning method.

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The return statement is valid only because it is inside an if block, since void methods cannot return elsewhere.

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The return statement implicitly returns the value 0 because the method's parameter is an int.

Question 9

A developer is writing a method that prints the numbers 1 through 5. The method must stop printing as soon as the number 3 has been printed, without printing any further numbers. Which loop control statement should be used inside the loop body when the current value equals 3?

Accepted Answer

break;. The break statement exits the innermost loop immediately, which is exactly what is needed to stop printing after the value 3. The continue statement only skips the current iteration and would keep printing later values, while return and System.exit are too broad, ending the method or the whole JVM rather than just the loop.

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return;

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continue;

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System.exit(0);

Question 10

A developer writes a class Vehicle with a protected method startEngine(). A class Car in a different package extends Vehicle. Inside a method of Car, the developer attempts to call startEngine() on a Vehicle reference variable named v. What happens at compile time?

Accepted Answer

The call fails to compile because protected access from another package requires the reference type to be Car or a subtype.. Across packages, a subclass may reach inherited protected members only through a reference whose declared type is that subclass or a subtype. Because the variable is typed as Vehicle, the compiler rejects the protected call even though Car inherits startEngine().

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The call compiles because protected members are effectively public to all subclasses in every package.

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The call compiles because Car inherits startEngine() from Vehicle.

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The call compiles only if startEngine() is also declared final in Vehicle.

Question 11

A developer defines a class Shape with a protected method area() and a public method describe() that calls area(). A subclass Circle overrides area() but does not override describe(). A Circle object is created and describe() is invoked. What happens?

Accepted Answer

The describe() method from Shape runs and calls Circle's overridden area().. Inheritance allows Circle to reuse the public describe() method from Shape. When describe() invokes area(), Java performs dynamic dispatch based on the runtime object, so the override in Circle executes. No compile error or exception occurs because describe() is inherited and area() is accessible from the declaring class.

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The describe() method from Shape runs and calls Shape's original area().

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A runtime exception is thrown because Circle did not override describe().

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A compile-time error occurs because describe() cannot call a protected method.

Question 12

A developer defines a method to compute the average of an int array: public static double average(int[] values). The developer calls average(3, 7, 11) and the code fails to compile. What is the reason?

Accepted Answer

The method must be declared with a varargs parameter to accept individual int arguments. A method parameter written as int[] values accepts exactly one array reference. Supplying three separate int literals gives the compiler three arguments where it expects one array, so the invocation does not match any available signature. Declaring the parameter with varargs, int... values, would allow the identical call to compile by building the array automatically.

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The method must be declared static before it can be called with literal values

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Integer literals cannot be passed to a method expecting an array of int

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The return type double is incompatible with an int array parameter

Question 13

A developer writes the following method:

public static void countDown(int start) {
    while (start > 0) {
        System.out.print(start + " ");
        start--;
    }
    System.out.println("Liftoff!");
}

What is printed when countDown(3) is called?

Accepted Answer

3 2 1 Liftoff!. The loop prints the current value and then decrements, so with an initial value of 3 it prints 3, 2, and 1 before the condition fails at 0. The Liftoff! message is printed once after the loop ends. The zero value is never printed because the condition is evaluated before each iteration.

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The method never terminates because start is decremented after it is printed.

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Liftoff! 3 2 1

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3 2 1 0 Liftoff!

Question 14

A developer wants to model a class Employee that stores a name and a salary. The class should prevent direct modification of salary from outside the class, while allowing read access. Which design best satisfies this requirement?

Accepted Answer

Declare salary as private and provide a public getter method; do not provide a setter.. Encapsulation uses private fields with controlled access. Keeping salary private and exposing only a public getter allows read access while blocking direct writes. Not providing a setter is the simplest way to prevent modification. A public or protected field, or a public setter, would allow unwanted changes from outside the class.

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Declare salary as private and provide a public getter and a public setter.

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Declare salary as protected and provide a public getter method.

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Declare salary as public and provide a public getter method.

Question 15

A developer writes a loop that should print the integers 0 through 4 inclusive. The code is: for (int i = 0; i < 5; i++) { System.out.print(i + " "); } Which statement accurately describes the output and the loop's behavior?

Accepted Answer

It prints 0 1 2 3 4 and terminates normally.. The three-part for header initializes i to 0, tests i < 5 before each pass, and increments i after each pass, so the body executes for 0, 1, 2, 3, and 4. Once i becomes 5 the test fails and control moves past the loop. The output is therefore the five integers 0 through 4 followed by normal completion.

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It prints 1 2 3 4 5 because i is pre-incremented before the first iteration.

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It fails to compile because i is declared inside the for statement.

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It prints 0 1 2 3 4 5 because the condition is checked after the increment.