1Z0-811 Practice Test 31 — 15 Questions

Question 1

A developer is writing a Java method that must return the smallest even number in an int array. If no even number exists, the method must return -1. The developer writes:

public static int firstEven(int[] nums) {
    for (int i = 0; i < nums.length; i++) {
        if (nums[i] % 2 == 0) {
            return nums[i];
        }
    }
    return -1;
}

Which statement describes the behavior of this method?

Accepted Answer

The method returns the first even number encountered in the array, not necessarily the smallest even number.. The loop exits as soon as an even value is found, so the method returns the first even element in index order. That value is only the smallest if the array happens to be sorted ascending. Finding a minimum requires explicit comparison against a running candidate, or sorting the array before the search.

Answer

The method returns -1 whenever the array is not sorted in ascending order.

Answer

The method returns the smallest even number because the loop visits elements in ascending index order.

Answer

The method always returns -1 because the return statement inside the loop is unreachable.

Question 2

A developer installs a JDK on a workstation and wants to write, compile, and run a small console program named Inventory.java. Which statement correctly describes the relationship between the tools they will use and the components of the Java platform in this workflow?

Accepted Answer

The JDK contains the JRE plus development tools, so it supports both compiling and running the program.. The Java Development Kit bundles a runtime environment together with developer utilities, so a single JDK installation covers writing, compiling, and executing code. The runtime-only package can execute bytecode but lacks the compiler and other tools, and the virtual machine by itself cannot translate source text. The JDK's superset relationship to the runtime is the deciding factor for this scenario.

Answer

The JVM alone is enough, because it compiles source files the first time they are executed.

Answer

The JDK and JRE are unrelated products, and only the JRE can launch a compiled class.

Answer

The JRE includes javac, so installing only the JRE is sufficient to compile Inventory.java.

Question 3

A developer defines an abstract class 'Shape' with an abstract method 'area()' and a concrete method 'describe()'. A subclass 'Rectangle' extends 'Shape' and provides an implementation of 'area()' but does not override 'describe()'. A program creates a 'Rectangle' object and calls both methods. What is the result?

Accepted Answer

The code compiles and runs; 'area()' executes the Rectangle implementation and 'describe()' executes the inherited Shape implementation.. A concrete subclass must implement all inherited abstract methods, which Rectangle does by providing 'area()'. Concrete methods such as 'describe()' are inherited and may be used without overriding. Because Rectangle is fully concrete, it can be instantiated, and calls to both methods succeed, with 'area()' using dynamic dispatch to select Rectangle's version.

Answer

The code fails to compile because Rectangle must override every method declared in Shape, including the concrete 'describe()' method.

Answer

The code fails to compile because Rectangle cannot be instantiated since it does not explicitly declare a constructor.

Answer

The code compiles but throws an AbstractMethodError at runtime when 'describe()' is called on the Rectangle object.

Question 4

A developer is reviewing code that declares several variables for a sensor-monitoring application. Which two declarations are valid in Java? (Choose two.)

Accepted Answer

char status = 'A';. A char literal in single quotes is valid, and a long literal with the L suffix assigned to a long variable is valid. The boolean type does not accept numeric values, a double literal cannot be assigned to a float without a suffix or cast, and 200 exceeds the byte range. These rules reflect Java's strict compile-time type checking for primitive literals.

Answer

boolean active = 1;

Answer

float reading = 3.14;

Answer

byte count = 200;

Question 5

A developer copies a compiled class file from a Windows workstation to a Linux server, then runs it with the java launcher. The program starts and behaves identically on both systems. A colleague claims this proves the class file contains Linux machine instructions. Which explanation best accounts for the observed behaviour?

Accepted Answer

The class file holds bytecode that the Linux JVM translates for its own processor at runtime.. Portability comes from the class file carrying bytecode defined by the virtual machine specification, leaving each JVM implementation to map those instructions onto its own host. The Linux JVM interprets or just-in-time compiles the very same artifact that the Windows JVM handled, producing equivalent program behaviour. No native code, source file, or emulated processor is involved in the transfer.

Answer

The class file contains Windows machine code, and Linux executes it through a compatibility layer.

Answer

The class file contains instructions for a virtual processor that both JVMs emulate identically.

Answer

The JVM recompiles the original source on the Linux host when the class is first loaded.

Question 6

A developer writes a method that parses a user-supplied string into an int using Integer.parseInt. The method must signal to its caller that parsing may fail with a NumberFormatException, but the developer wants callers to be forced to handle or declare it. Which change should the developer make to the method signature?

Accepted Answer

Wrap the parseInt call in a try-catch block and throw a new checked exception, declaring that checked exception in the method signature.. Unchecked exceptions such as NumberFormatException are not subject to the catch-or-declare requirement, so merely declaring it does not force callers to handle it. To impose that requirement, the method must throw a checked exception instead, which the compiler then enforces. Wrapping the parse call and throwing a checked exception, with that exception declared in the signature, is the only listed change that accomplishes this.

Answer

Declare the method with a generic type parameter bound to Exception.

Answer

Annotate the method with @Override to indicate it may throw an exception.

Answer

Add throws NumberFormatException to the method signature.

Question 7

A developer is reviewing a method that searches a two-dimensional int array for a target value. The method must return true if the target appears anywhere in the array. Which two statements about passing and using a two-dimensional array as a method parameter are correct? (Choose two.)

Accepted Answer

The parameter can be declared as int[][] grid, and grid.length gives the number of rows.. A two-dimensional array parameter can be written as int[][] grid or equivalently as int grid[][]. The outer array's length gives the row count, and each row is itself an array whose length gives the column count. Arrays are objects passed by reference value, so no deep copy occurs, and varargs is unrelated to passing 2D arrays.

Answer

The method receives a deep copy of the array, so modifications to grid inside the method do not affect the caller's array.

Answer

The parameter must be declared as int... grid because two-dimensional arrays cannot be passed directly to methods.

Answer

Inside the method, grid.length returns the total number of elements across all rows.

Question 8

A developer at a logistics company defines this method:

public static void addFee(double[] charges) {
    charges = new double[]{5.0, 10.0};
    charges[0] = 99.0;
}

It is invoked as:

double[] fees = {1.0, 2.0};
addFee(fees);
System.out.println(fees[0]);

What is printed?

Accepted Answer

1.0. Because Java is strictly pass-by-value, the method receives a copy of the reference. Reassigning that parameter to a new array disconnects it from the caller's object, so the later element write is invisible to the caller. Only mutating the aliased object itself, without reassigning the parameter, would change fees[0].

Answer

99.0

Answer

A NullPointerException is thrown.

Answer

5.0

Question 9

A developer needs to search a two-dimensional array of sensor readings for a target value and stop scanning as soon as the value is found. The code is:

```java
int[][] grid = {{1, 2}, {3, 4}};
int target = 3;
boolean found = false;
for (int r = 0; r < grid.length; r++) {
    for (int c = 0; c < grid[r].length; c++) {
        if (grid[r][c] == target) {
            found = true;
            break;
        }
    }
}
```

What is the effect of the break statement in this code?

Accepted Answer

It exits only the inner loop, and the outer loop continues with the next row.. An unlabeled break transfers control out of the innermost enclosing loop, which in this nested structure is the column loop. The row loop then continues to the next iteration, so the search does not truly stop at the first match across the whole grid. Only a labeled break naming the outer loop would abandon both loops at once.

Answer

It terminates the current method and returns control to the caller.

Answer

It exits both loops immediately, because break always terminates all enclosing loops.

Answer

It causes a compile-time error, because break cannot appear inside a nested loop.

Question 10

A developer wants to compile and run a Java program from the command line. The source file is named Hello.java and contains a single public class Hello. Which command correctly compiles the source file?

Accepted Answer

javac Hello.java. The Java compiler is invoked with the javac command, which takes source file names including the .java extension. The java command is used to run compiled classes. Therefore, javac Hello.java is the correct way to compile the source file into bytecode.

Answer

javac Hello

Answer

java Hello.class

Answer

java Hello.java

Question 11

A developer is designing a Shape class hierarchy for a graphics editor. The Shape class declares a method public double area() that returns 0.0. The Circle subclass provides its own area() implementation. When the developer writes Shape s = new Circle(2.0); System.out.println(s.area()); the program prints the circle's area. Which OOP concept does this behavior demonstrate?

Accepted Answer

Dynamic method dispatch. Because Circle overrides Shape's area() and the call is made through a Shape reference holding a Circle object, the JVM defers the method selection until runtime and executes Circle's implementation. This runtime selection based on the actual object type is dynamic method dispatch, the cornerstone of polymorphic behavior in Java.

Answer

Static binding of the area method

Answer

Method overloading

Answer

Encapsulation

Question 12

A developer writes a class named Employee that declares a public method named calculatePay. A second class named Manager extends Employee and declares its own public method named calculatePay with the exact same name, parameter list, and return type. At runtime, a Manager object assigned to an Employee reference is used to invoke calculatePay. Which concept does this scenario describe?

Accepted Answer

Method overriding. Because Manager supplies calculatePay with the same signature as the inherited method, it overrides the superclass implementation. A call through an Employee reference that points to a Manager object is resolved at runtime to Manager's version, which is runtime polymorphism. Overloading, hiding, and encapsulation describe different mechanisms and do not explain this behavior.

Answer

Encapsulation

Answer

Method hiding

Answer

Method overloading

Question 13

A developer writes a class Employee with fields name and salary. The developer wants other classes to read and modify these fields only through methods that enforce validation rules, and wants to prevent direct field access from outside the class. Which pair of keywords should be applied to the fields and the accessor methods respectively to achieve this?

Accepted Answer

private on the fields and public on the accessor methods. Encapsulation requires hiding internal state and exposing only controlled operations. Private fields stop outside code from writing values that skip validation, while public accessor methods provide the single sanctioned path where rules such as non-negative salary can be enforced before assignment.

Answer

public on the fields and public on the accessor methods

Answer

final on the fields and static on the accessor methods

Answer

protected on the fields and private on the accessor methods

Question 14

A developer is writing a method that accepts a two-dimensional array of sensor readings and returns the average of the first row. The parameter is declared as int[][] grid. Which expression correctly obtains the number of columns in the first row of the argument?

Accepted Answer

grid[0].length. A two-dimensional array is an array of arrays, so the outer length gives the row count while the length of any indexed row gives that row's column count. Since rows may differ in size, reading grid[0].length is the reliable way to size a loop over the first row.

Answer

grid.length[0]

Answer

grid.length

Answer

grid[0][0].length

Question 15

A developer is writing a payroll system. The class `Employee` has a method `calculatePay()`, and the subclass `Manager` overrides it to add a bonus. The developer writes `Employee e = new Manager();` and then calls `e.calculatePay();`. Which statement describes what happens at runtime?

Accepted Answer

The Manager version of calculatePay() executes because the object's actual type determines the overridden method invoked.. Overridden instance methods are resolved at runtime from the actual object type, not the declared reference type. Because the object created is a Manager, the Manager implementation of calculatePay() runs even though the variable is typed as Employee. This is runtime polymorphism in action, and the assignment from subclass to superclass reference is always permitted without a cast.

Answer

The Employee version of calculatePay() executes because the reference variable is declared as Employee.

Answer

The code fails to compile because a superclass reference cannot be assigned to a subclass object.

Answer

The code throws a ClassCastException at runtime when calculatePay() is invoked.