1Z0-811 Practice Exam 2 — 20 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;

Question 11

int count = 0;
for (int i = 0; i < 5; i++) {
    if (i == 2) {
        continue;
    }
    count++;
}
System.out.println(count);

What is the output of the program?

Accepted Answer

4. The loop runs i from 0 to 4. When i equals 2, the continue statement skips the rest of the loop body, so count++ is not executed for that iteration. For the other four iterations (i = 0, 1, 3, 4), count is incremented, giving a final value of 4.

Answer

The loop does not compile.

Answer

5

Answer

2

Question 12

Given: boolean a = false; boolean b = true; boolean c = true; System.out.println(a || b && c); What is the output?

Accepted Answer

true. In Java, the logical AND operator (&&) has higher precedence than the logical OR operator (||). Therefore, the expression `a || b && c` is evaluated as `a || (b && c)`. Given `a = false`, `b = true`, and `c = true`, `b && c` evaluates to `true`, and then `false || true` evaluates to `true`. Thus, the output is `true`, making option D correct.

Answer

false

Answer

Compilation fails

Answer

None of the above

Question 13

A developer compiles a Java application using the command `javac -d bin src/com/example/App.java`. Which of the following is true?

Accepted Answer

The compiled .class files are placed in the `bin` directory maintaining the package structure.. The `-d` option in the `javac` command specifies the destination directory for compiled `.class` files. When `-d bin` is used, the compiler places the `.class` files into the `bin` directory, preserving the package directory structure (e.g., `bin/com/example/App.class`). This is the standard behavior for organizing compiled output separately from source code.

Answer

The compiler searches for source files in the `bin` directory.

Answer

The compiler creates a JAR file named `App.jar` in the `bin` directory.

Answer

The compiler compiles the code into a named module.

Question 14

Which of the following correctly uses the shorthand array initializer to declare and initialize an array of strings with the elements "A", "B", and "C"?

Accepted Answer

String[] arr = {"A", "B", "C"};. Option D correctly uses the shorthand array initializer with curly braces directly in the declaration. Option A uses the full syntax with the 'new' keyword, which is also valid but not the shorthand. Option B is wrong because it uses parentheses. Option C is wrong because it uses square brackets.

Answer

String[] arr = new String[] {"A", "B", "C"};

Answer

String[] arr = ("A", "B", "C");

Answer

String[] arr = ["A", "B", "C"];

Question 15

Given the code: String s1 = "Java"; String s2 = new String("Java"); if (s1 == s2) { System.out.print("Equal"); } else { System.out.print("Not Equal"); } What is the output?

Accepted Answer

Not Equal. The == operator compares object references, not the actual string content. s1 is a string literal stored in the string pool, while s2 is a new String object created on the heap, so they refer to different memory locations, making the comparison false and printing 'Not Equal'.

Answer

Runtime error

Answer

Compilation error

Answer

Equal

Question 16

A developer is working on a Java application that processes sensor data. The code uses a class 'SensorDataProcessor' which directly instantiates specific sensor classes like 'TemperatureSensor' and 'PressureSensor' inside its methods. The team wants to make the system extensible to support new sensor types without modifying the processor class. Which design change best achieves this?

Accepted Answer

Define a Sensor interface and use dependency injection to pass sensor objects to the processor. The Open/Closed Principle says classes should be open for extension but closed for modification. By defining a Sensor interface and injecting Sensor implementations into SensorDataProcessor, the processor depends on an abstraction rather than concrete classes, so new sensor types can be added without touching the processor code. Dependency injection also improves testability because mock sensors can be substituted in unit tests. This is the canonical Strategy/DI pattern for decoupling.

Answer

Make SensorDataProcessor abstract and subclass it for each sensor

Answer

Use a static factory method in SensorDataProcessor to create sensors

Answer

Create a separate configuration file listing sensors and use reflection to instantiate them

Question 17

A developer writes a utility that must return two values, a minimum and a maximum, from an array of measurements. The method below is proposed:

public static int[] minMax(int[] values) {
    // implementation omitted
    return new int[]{min, max};
}

Which statement about this method signature and return statement is correct?

Accepted Answer

The method compiles, and the returned array is a distinct object whose length is 2.. Array types are legitimate return types because arrays are objects, and an array initializer on a return statement allocates a brand-new two-element array on each invocation. The caller therefore receives an independent object whose length is fixed at two by the initializer.

Answer

The method compiles only if the array initializer is replaced with a call to Arrays.copyOf on the input parameter.

Answer

The method cannot compile because Java methods may return only primitive values or single objects, never arrays.

Answer

The method compiles, but the returned array automatically shares storage with the input parameter values.

Question 18

Which THREE of the following expressions compile without error? (Choose 3)

Accepted Answer

byte b = 1 + 2;. Option A is correct because the expression 1 + 2 is a compile-time constant int whose value (3) fits within the byte range, so the implicit narrowing assignment to byte is permitted. Option C is correct because an int literal 10 is widened automatically to double in the assignment double d = 10;. Option D is correct because (false || true) is a valid boolean expression using the logical OR operator, and its result is assignable to a boolean variable. Option B is not correct because 5L is a long and 10 is an int; the sum is long, which cannot be assigned to an int without an explicit cast. Option E is not correct because 5.5 is a double literal, and assigning a double to a float requires an explicit cast (or an f suffix such as 5.5f).

Answer

int i = 5L + 10;

Answer

float f = 5.5;

Question 19

Which operator is used to compare two strings for value equality in Java?

Accepted Answer

equals(). The equals() method in Java's String class compares the actual character sequences of two strings for value equality. Unlike the == operator, which checks reference equality (whether two references point to the same object in memory), equals() performs a lexicographic comparison of the string contents, returning true if and only if both strings have the same length and the same characters in the same order.

Answer

compareTo()

Answer

=

Answer

==