1Z0-811 Practice Test 3 — 10 Questions

Question 1

A package named com.example.util is declared in a file. Where should the file be placed in the directory structure?

Accepted Answer

com/example/util/. Java requires that the directory structure of a package matches the package declaration. A package named `com.example.util` must be stored in a directory hierarchy `com/example/util/` so that the Java compiler and runtime can locate the class files based on the fully qualified name. This ensures that the file is accessible via the classpath or module path.

Answer

com.example.util/

Answer

util/

Answer

com/example/util.java

Question 2

Arrange the steps to create and use a simple Java inheritance hierarchy in the correct order.

Accepted Answer

Create the superclass, then create the subclass with extends, then override methods if needed, then add new members, then use the subclass.. First create the superclass, then create subclass with extends, override methods if needed, add new members, and then use the subclass.

Answer

Create the subclass, then create the superclass, then override methods, then add new members, then use the subclass.

Answer

Create the superclass, then create the subclass with extends, then add new members, then override methods, then use the subclass.

Answer

Create the superclass, then create the subclass without using extends (copy code), then override methods, then add new members, then use the subclass.

Question 3

Given the stack trace above, which line in MyClass.java caused the exception?

Exception in thread "main" java.lang.NullPointerException
    at MyClass.methodC(MyClass.java:25)
    at MyClass.methodB(MyClass.java:15)
    at MyClass.methodA(MyClass.java:10)
    at MyClass.main(MyClass.java:30)

Accepted Answer

Line 25. The stack trace displayed in the question shows the exception was thrown at line 25 of MyClass.java. The topmost line in a stack trace indicates the exact line where the exception originated. Lines 10, 15, and 30 correspond to caller methods that appear lower in the stack trace, making line 25 the correct answer.

Answer

Line 30

Answer

Line 10

Answer

Line 15

Question 4

Which of the following correctly uses the ternary operator to set int max to the larger of two ints x and y?

Accepted Answer

int max = x > y ? x : y;. The ternary operator `? :` evaluates the boolean expression `x > y`; if true, it returns `x`, otherwise `y`, assigning the larger value to `int max`. This is the standard syntax for a conditional assignment in Java, as defined in the Java Language Specification (JLS §15.25).

Answer

int max = x > y ? y : x;

Answer

int max = if (x > y) x else y;

Answer

int max = (x > y) ? x, y;

Question 5

Given: String str = "Java"; str = str.concat(" SE"); str.replace('a', 'A'); System.out.println(str); What is the output?

Accepted Answer

Java SE. The `concat` method returns a new String "Java SE" which is assigned back to `str`. The `replace` method also returns a new String but its result is not assigned to any variable, so the original `str` remains unchanged. The final `println` outputs the current value of `str`, which is "Java SE".

Answer

Java

Answer

JAVA SE

Answer

JAvA SE

Question 6

Which design principle is violated by making all fields public in a class?

Accepted Answer

Encapsulation. Making all fields public violates the principle of encapsulation, which requires that an object's internal state be hidden from external access and only modifiable through controlled methods (getters/setters). In Java, public fields allow any class to directly read or modify the field, breaking data integrity and the ability to enforce invariants. Encapsulation is a core OOP concept that protects the internal representation of an object.

Answer

Inheritance

Answer

Abstraction

Answer

Polymorphism

Question 7

A developer is working on a Java program that processes sensor data. The data is stored in a 2D array 'double[][] readings', where each row represents a sensor and each column a time interval. The method 'public static double[] averagePerSensor(double[][] data)' should compute the average reading for each sensor (row) and return a 1D array of averages. The developer writes the following implementation: 'double[] result = new double[data.length]; for (int i = 0; i < data.length; i++) { double sum = 0; for (int j = 0; j < data[i].length; j++) { sum += data[i][j]; } result[i] = sum / data[i].length; } return result;'. However, the program sometimes throws a NullPointerException. What is the most likely cause?

Accepted Answer

One or more rows in the 2D array are null.. The NullPointerException occurs because the code attempts to access `data[i].length` when `data[i]` is null. In Java, a 2D array is an array of arrays, and any row can be null. The code does not check for null rows before iterating over the columns, so if a row is null, accessing `data[i][j]` or `data[i].length` throws a NullPointerException. Option C correctly identifies this as the most likely cause.

Answer

The method returns a double[] but should return double[][].

Answer

The rows have different numbers of columns.

Answer

The outer loop uses data[i].length instead of data.length.

Question 8

Which of the following scenarios demonstrates the most appropriate use of a continue statement?

Accepted Answer

Skipping the current iteration and moving to the next when a condition is met. The `continue` statement in Java is specifically designed to skip the remaining code in the current iteration of a loop and proceed directly to the next iteration. This is the most appropriate use case, as it allows you to bypass certain iterations based on a condition without breaking out of the loop entirely.

Answer

Restarting the loop from the beginning

Answer

Implementing fall-through in a switch statement

Answer

Exiting a loop early when a condition is met

Question 9

A developer is writing a switch statement in Java to route a shipment based on a String region code. Which two statements about this switch statement are true? (Choose two.)

Accepted Answer

Each case label must be a compile-time constant expression, and duplicate labels in the same switch cause a compile-time error.. Java allows String switch expressions and compares them by content, so equal text selects the same case even for distinct objects. Case labels must be compile-time constants and must be unique within the switch. Fall-through, not automatic termination, occurs when break is omitted, and the default label remains optional rather than mandatory.

Answer

If a matching case has no break statement, execution stops automatically at the end of that case.

Answer

The default label is required in every switch statement, and omitting it prevents compilation.

Answer

A switch on a String can only be used inside a method that declares throws Exception.

Question 10

In a Java method, a developer needs to skip the current iteration and move to the next when a certain condition is met inside a for loop. Which statement should be used?

Accepted Answer

continue;. The `continue` statement in Java immediately skips the remaining code in the current iteration of a loop and proceeds to the next iteration. This is exactly what the developer needs when a condition is met inside a `for` loop to move to the next cycle without executing further statements in the current iteration.

Answer

return;

Answer

exit;

Answer

break;