1Z0-811 Practice Test 11 — 15 Questions

Question 1

Which THREE statements are true about method overloading in Java?

Accepted Answer

The return type can be different, but it is not sufficient to differentiate overloaded methods.. Option B is correct because Java allows overloaded methods to declare different return types, but the return type alone cannot distinguish two overloads — the compiler uses only the method name and parameter list (signature) for overload resolution, so two methods differing only in return type cause a compile-time error. Option D is correct because overloading is typically achieved by declaring multiple methods with the same name but different parameter lists within the same class (inherited methods can also participate, but same-class definition is valid and common). Option E is correct because the defining requirement for overloaded methods is that their parameter lists differ in number, type, or order; identical parameter lists with the same name are not overloads. Option A is incorrect because methods with the same name and same parameter types but different return types are not valid overloads and will not compile. Option C is incorrect because method overloading is resolved at compile time (static binding) based on the compile-time types of the arguments, unlike overriding which is resolved at runtime.

Answer

Two methods with the same name, same parameter types, but different return types are overloaded.

Answer

Method overloading is resolved at runtime.

Question 2

Which two statements about passing arrays to methods are correct? (Select two.)

Accepted Answer

Modifying the array elements inside the method affects the original array.. Option C is correct because in Java an array is an object, and the method receives a copy of the reference that points to the same underlying array object, so changing elements such as arr[0] = 5 inside the method is visible through the caller's original reference. Option E is correct because Java is strictly pass-by-value: for an array parameter, the value that is copied is the reference (the memory address) to the array object, not the array contents themselves. Option A is wrong because passing an array passes one reference value, not a copy of each element, so element-level changes are shared rather than independent. Option B is wrong because array length is fixed at creation; a method cannot resize the caller's original array, it can only create a new array. Option D is wrong because reassigning the parameter to a new array only changes the local copy of the reference, leaving the caller's original reference pointing to the old array.

Answer

Passing an array is the same as passing each element individually.

Answer

The method can change the size of the original array.

Answer

If the method assigns a new array to the parameter, the original reference is updated outside the method.

Question 3

A developer uses a switch statement with a String variable. Which is true about this usage?

Accepted Answer

It works with strings starting from Java 7. Starting from Java 7 (JSR 334), the switch statement supports String objects in addition to primitive types and enums. The compiler uses the `hashCode()` and `equals()` methods of the String class to evaluate the switch expression against case labels, making it a valid and efficient way to branch on string values.

Answer

It works only with primitive types

Answer

It causes a compilation error because strings are not supported

Answer

It requires a default case

Question 4

A method 'public static void sort(int[] arr)' sorts the array in place. After calling 'sort(data)', the original array 'data' is changed. Which design issue does this demonstrate?

Accepted Answer

The method should return a new array to avoid side effects.. The method modifies the original array passed as an argument, which is a side effect. In Java, arrays are objects, and when passed to a method, the reference is passed by value, allowing the method to modify the array's contents. To avoid side effects and maintain immutability, the method should return a new sorted array instead of modifying the original.

Answer

The method should use a wrapper class for the array.

Answer

The method should be declared as void to indicate modification.

Answer

The method should use pass-by-value to avoid modification.

Question 5

Refer to the exhibit. A Java source file fails to compile with the given error. What change should be made to fix the error?

Accepted Answer

Add a throws IOException clause to the enclosing method. The code is calling a method (e.g., `Files.readString()`, `BufferedReader.readLine()`, or similar) that throws a checked `IOException`. In Java, checked exceptions must be either caught with a try-catch block or declared in the enclosing method's `throws` clause. Option A adds the `throws IOException` declaration, which correctly propagates the exception to the caller, satisfying the compiler's requirement.

Answer

Wrap the code in a try-catch for NullPointerException

Answer

Change the method to use a finally block

Answer

Import the java.io.IOException class

Question 6

Which TWO statements about constructors are true? (Choose two.)

Accepted Answer

Constructors have no return type. Option A is correct because a constructor is declared without any return type — not even void — since its purpose is only to initialize a new object, and the JVM treats it specially during object creation. Option C is correct because the compiler implicitly inserts a no-argument default constructor only when the class defines no constructors at all; as soon as any constructor is declared, no default is generated. Option B is wrong because the compiler does not "always" provide a default constructor — it is suppressed once any constructor is explicitly defined. Option D is wrong because constructors cannot be abstract; they are never inherited or overridden, so abstract (which requires overriding) is illegal on a constructor. Option E is wrong because constructors have no return type whatsoever, and explicitly writing void would turn the declaration into a regular method rather than a constructor.

Answer

The compiler always provides a default constructor

Answer

Constructors can be declared as abstract

Answer

Constructors have a return type of void

Question 7

Which loop best suits a scenario where the number of iterations is unknown and depends on user input?

Accepted Answer

while loop. The while loop is best when the number of iterations is unknown and depends on user input because it evaluates a boolean condition before each iteration, allowing the loop to continue as long as the condition remains true. This is ideal for scenarios like reading user input until a sentinel value is entered, where the exact number of iterations cannot be predetermined.

Answer

for loop

Answer

for-each loop

Answer

do-while loop

Question 8

What is the result of the expression 10 % 3?

Accepted Answer

1. The modulo operator (%) in Java returns the remainder of the division of the left operand by the right operand. Since 10 divided by 3 equals 3 with a remainder of 1, the expression 10 % 3 evaluates to 1.

Answer

3.33

Answer

0

Answer

3

Question 9

A scientific application performs calculations with double precision. A specific formula divides two double values: result = a / b; where a and b are calculated from sensor readings. The result is expected to be at most 10 decimal digits of precision. However, the output often shows small rounding errors, e.g., 0.1 + 0.2 = 0.30000000000000004. The application must meet strict accuracy requirements and cannot tolerate these small errors. Which strategy should be used to achieve exact decimal representation?

Accepted Answer

Use BigDecimal with an appropriate scale and rounding mode.. Floating-point arithmetic (double) inherently has rounding errors due to binary representation, as shown in the example 0.1 + 0.2 = 0.30000000000000004. BigDecimal provides arbitrary-precision decimal arithmetic and allows specifying scale and rounding modes, making it ideal for exact decimal calculations meeting the 10-digit precision requirement. Therefore, Option A (BigDecimal) is the correct approach. Option B (Math.round) rounds to an integer, losing fractional precision. Option C (float) uses less precision than double, worsening errors. Option D (casting to int after scaling) truncates and risks loss of information.

Answer

Apply Math.round() to the result to reduce decimal places.

Answer

Use the float data type instead of double to reduce memory usage.

Answer

Cast the result to int after multiplying by a power of 10.

Question 10

A team is designing a Java application that needs to run on different operating systems without modification. Which Java feature makes this possible?

Accepted Answer

The Java Virtual Machine. The Java Virtual Machine (JVM) is the key enabler of Java's 'write once, run anywhere' capability. When you compile Java source code, the Java compiler produces bytecode, which is platform-independent. This bytecode is then executed by the JVM, which is implemented specifically for each operating system (Windows, Linux, macOS, etc.), translating the bytecode into native machine instructions. Therefore, the same compiled .class file can run on any OS that has a compatible JVM, without requiring any modifications to the application code.

Answer

Just-in-time compilation

Answer

Garbage collection

Answer

The Java compiler

Question 11

A developer writes the following code: if (score >= 90) { grade = 'A'; } else if (score >= 80) { grade = 'B'; } else if (score >= 70) { grade = 'C'; } else { grade = 'D'; } What is the value of grade if score is 75?

Accepted Answer

'C'. The code uses a cascading if-else-if structure that evaluates conditions from top to bottom. When score is 75, the first condition (score >= 90) is false, the second (score >= 80) is false, and the third (score >= 70) is true, so grade is assigned 'C'. The else block is only reached if all prior conditions are false.

Answer

'B'

Answer

'D'

Answer

'A'

Question 12

Given the code snippet: int x = 5; int y = 2; double result = x / y; What is the value of result?

Accepted Answer

2.0. In Java, when both operands of the division operator are integers (int), integer division is performed, which truncates the fractional part. Here, x / y evaluates to 5 / 2 = 2 (integer division), and then the int value 2 is implicitly widened to double 2.0 when assigned to the double variable result.

Answer

Compilation fails

Answer

2.5

Answer

2

Question 13

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 14

Given the code fragment:

```java
int[] data = {1, 2, 3, 4, 5};
int sum = 0;
for (int i = 0; i <= data.length; i++) {
    sum += data[i];
}
System.out.println(sum);
```

What is the result?

Accepted Answer

ArrayIndexOutOfBoundsException. The loop condition i <= data.length causes i to become 5 when data.length is 5, but valid indices are 0-4. This results in an ArrayIndexOutOfBoundsException. Option A is wrong because the exception occurs before sum reaches 15. Option C is wrong because sum is not 0. Option D is wrong because the code compiles successfully.

Answer

15

Answer

0

Answer

Compilation fails

Question 15

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