1Z0-811 Practice Test 21 — 15 Questions

Question 1

What is the result of: System.out.println(10 + 20 + "30");

Accepted Answer

3030. In Java, the '+' operator is left-associative. The expression `10 + 20 + "30"` is evaluated as `(10 + 20) + "30"`, which first performs integer addition to get `30`, then concatenates that integer with the string `"30"`, resulting in the string `"3030"`. The `System.out.println` method then prints the string `3030`.

Answer

102030

Answer

30

Answer

Compilation fails

Question 2

Arrange the steps to create an object from a class in Java in the correct order.

Accepted Answer

Define the class, then declare a variable, then instantiate with new, then assign to variable, then use the object.. First define the class, then declare a variable, instantiate with new, assign to variable, and then use the object.

Answer

Define the class, then instantiate the object, then declare a variable, then assign to variable, then use the object.

Answer

Declare a variable, then define the class, then instantiate the object, then assign to variable, then use the object.

Answer

Instantiate the object, then define the class, then declare a variable, then assign to variable, then use the object.

Question 3

What is the result of: int[] arr = new int[5]; System.out.println(arr[5]);

Accepted Answer

ArrayIndexOutOfBoundsException. Java arrays are zero-indexed, meaning a valid index for an array of length 5 is 0 through 4. Accessing index 5 throws an ArrayIndexOutOfBoundsException at runtime, as it is outside the array's bounds.

Answer

null

Answer

-1

Answer

0

Question 4

A team is developing a Java application that uses many third-party libraries. One library throws a checked exception that is not declared in its method signature. Which approach best handles this situation?

Accepted Answer

Wrap the exception in a RuntimeException and throw it.. A checked exception that is not declared in a method signature cannot be propagated without handling it. Wrapping it in a RuntimeException (an unchecked exception) bypasses the compiler's checked-exception enforcement, allowing the exception to be thrown without modifying the method signature. This is a common pattern when integrating third-party libraries that throw checked exceptions from methods that do not declare them.

Answer

Ignore the exception because it is not declared.

Answer

Declare the library's exception in the method signature.

Answer

Catch the exception and log it, then continue execution.

Question 5

What is the default value of a boolean variable in Java?

Accepted Answer

false. In Java, the default value of a boolean variable (when declared as a class field or instance variable) is 'false'. This is specified by the Java Language Specification (JLS §4.12.5), which defines default values for all primitive types. Unlike local variables, which must be explicitly initialized, instance and static variables receive default values automatically.

Answer

null

Answer

true

Answer

0

Question 6

Given methods: void print(Integer i) { System.out.println("Integer"); } void print(int i) { System.out.println("int"); } What is output of print(10);?

Accepted Answer

"int". When calling print(10) with an integer literal, Java's method overloading resolution prefers the primitive int version over the Integer wrapper type because the literal 10 is a primitive int. The compiler selects the most specific matching method without requiring autoboxing, so the void print(int i) method is invoked, printing "int".

Answer

Compilation error

Answer

"Integer"

Answer

Runtime error

Question 7

A Java application uses a custom exception class that extends Exception. The application throws this exception from a method, but the method does not declare it in its throws clause. Which statement is true?

Accepted Answer

The code will not compile because checked exceptions must be declared.. In Java, a custom exception class that extends Exception (but not RuntimeException) is a checked exception. Checked exceptions must be either caught within the method using a try-catch block or declared in the method's throws clause. If the method throws a checked exception without declaring it, the code will not compile. This is enforced by the Java compiler to ensure that callers are aware of and handle potential exceptions.

Answer

The code will compile only if the exception is caught inside the method.

Answer

The code will compile and throw a RuntimeException if the exception occurs.

Answer

The code will compile because custom exceptions are unchecked.

Question 8

A development team is building a library management system. The system has classes 'LibraryItem', 'Book', and 'DVD'. LibraryItem has a method 'getTitle()' that returns the title. Book and DVD extend LibraryItem. The team wants to ensure that when a LibraryItem is borrowed, a message specific to its type is displayed. They have a 'Borrower' class with a method 'borrow(LibraryItem item)', which currently calls 'item.getTitle()' and prints the title. Now they need to display 'Book borrowed' or 'DVD borrowed' based on the actual item type. They want to avoid using 'instanceof' checks in the 'borrow' method to keep it open for new item types. Which design should they use?

Accepted Answer

Define an abstract method 'getBorrowMessage()' in LibraryItem, and implement it in Book and DVD. Call that method in borrow().. It applies the Open/Closed Principle: LibraryItem defines an abstract getBorrowMessage() method, and each subclass provides its own implementation. The borrow() method calls this polymorphic method without needing instanceof or type checks, so adding new item types (e.g., Magazine) only requires implementing getBorrowMessage() in the new subclass without modifying existing code.

Answer

Add a String field 'type' to LibraryItem and set it in each subclass constructor. In borrow(), check the field.

Answer

Use a switch statement on the class name in borrow().

Answer

Override the 'borrow' method in each subclass and call a different method.

Question 9

A developer creates an interface 'Drawable' with a single abstract method 'draw()'. They then create a class 'Circle' that implements Drawable but forgets to provide the draw() method. Circle is not declared abstract. What will happen when compiling Circle?

Accepted Answer

Compilation fails because Circle must either implement draw() or be declared abstract. A class that implements an interface must provide implementations for all abstract methods, or it must be declared abstract. Without the implementation and without being abstract, the class does not compile.

Answer

Compilation fails because interfaces cannot be implemented without overriding all methods

Answer

Compilation succeeds, a default empty method is generated

Answer

Compilation succeeds but a warning is issued

Question 10

Match each Java exception class to its category.

Accepted Answer

IOException: Checked Exception. Checked exceptions (e.g., IOException, ClassNotFoundException) must be handled or declared; unchecked exceptions (e.g., NullPointerException, ArithmeticException) are RuntimeExceptions and do not require explicit handling.

Answer

NullPointerException: Checked Exception

Answer

IOException: Unchecked Exception

Question 11

A developer writes: boolean b = !true && false; What is the value of b?

Accepted Answer

false. The expression `!true && false` is evaluated as `(!true) && false`, which is `false && false`. The logical AND (`&&`) operator returns `true` only if both operands are `true`; otherwise, it returns `false`. Therefore, `b` is assigned `false`. Option B is correct.

Answer

Compilation error: invalid operator.

Answer

NullPointerException

Answer

true

Question 12

A developer encounters an ArrayIndexOutOfBoundsException while running a unit test. The stack trace shows the error occurs in a method that is called from many places. Which tool or technique would most efficiently identify the specific call path?

Accepted Answer

Set a breakpoint in the method and debug the test.. Setting a breakpoint in the method and debugging the test allows the developer to inspect the call stack at runtime, immediately revealing the exact sequence of method invocations that led to the ArrayIndexOutOfBoundsException. This is the most efficient approach because it directly captures the specific call path without requiring manual tracing or post-hoc analysis.

Answer

Review the code manually to trace all possible callers.

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Run a static analysis tool to detect the issue.

Answer

Add log statements at the beginning of the method.

Question 13

A banking application has a base class 'Account' with a method 'withdraw()' marked as final. A subclass 'SavingsAccount' tries to override 'withdraw()'. What is the outcome?

Accepted Answer

Compilation error because final methods cannot be overridden. A final method cannot be overridden in a subclass. Attempting to do so results in a compilation error.

Answer

The override works only if SavingsAccount is in the same package

Answer

The override succeeds, final is ignored in subclasses

Answer

Runtime error when the method is called

Question 14

Which data type should be used to store a single character like 'A'?

Accepted Answer

char. In Java, the `char` data type is a single 16-bit Unicode character, capable of storing any character from the Unicode standard, including 'A'. It is the primitive type specifically designed for a single character, whereas `String` is a reference type for sequences of characters.

Answer

String

Answer

byte

Answer

int