1Z0-811 Practice Test 26 — 15 Questions

Question 1

What is the primary purpose of Java bytecode?

Accepted Answer

To be executed by the Java Virtual Machine on any platform. Java bytecode is designed to be executed by the Java Virtual Machine (JVM), which interprets or compiles it to native code for the underlying platform, enabling platform independence. Option B is incorrect because bytecode is an intermediate representation that is compiled or interpreted at runtime, not compiled once into native code for reuse across platforms. Option C is incorrect because bytecode is not human-readable source code; it is a binary format. Option D is incorrect because bytecode cannot be directly executed by the operating system; it requires the JVM to run.

Answer

To be compiled into native code once and reused

Answer

To be human-readable source code

Answer

To be directly executed by the operating system

Question 2

Which TWO are valid ways to create a String object?

Accepted Answer

String s = "hello";. Using a string literal ("hello") creates a String object automatically via the JVM's string constant pool, which is a standard and valid way. Option E is correct because the String constructor new String(String) takes another String as an argument, here "hello", which is valid. Option A is incorrect because null is not an object; it is a reference that does not point to any object. Option B is incorrect because the String constructor expects a String or other char sequence, not an int literal. Option D is incorrect because single quotes denote a char literal, not a String.

Answer

String s = null;

Answer

String s = new String(10);

Answer

String s = 'hello';

Question 3

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

Accepted Answer

==. The == operator in Java is used to compare two primitive values for equality, returning true if they are equal. For reference types, == compares object references (memory addresses), not the actual content. This is a fundamental operator defined in the Java Language Specification (JLS §15.21) for equality testing.

Answer

equals()

Answer

!=

Answer

=

Question 4

What is the result of the following code? Integer a = 100; Integer b = 100; System.out.println(a == b);

Accepted Answer

true. Java caches Integer objects for values between -128 and 127. When autoboxing converts the int literal 100 to an Integer object, both a and b reference the same cached object. Therefore, the == operator, which compares object references, returns true.

Answer

false

Answer

Compilation error

Answer

Runtime exception

Question 5

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 6

A developer writes the following code:

int a = 5;
int b = 2;
double result = a / b;
System.out.println(result);

What is the output?

Accepted Answer

2.0. In Java, when both operands of the division operator are integers (int), the operation performs integer division, which truncates the fractional part. Here, a (5) divided by b (2) yields 2, and then the result is implicitly widened to double when assigned to the variable result, producing 2.0.

Answer

2.5

Answer

Compilation fails

Answer

2

Question 7

A junior developer wrote a while loop that never terminates. What is the most likely cause?

Accepted Answer

The loop condition is always true. A while loop terminates only when its boolean condition evaluates to false. If the condition is always true, the loop will run indefinitely, causing an infinite loop. In Java, this typically happens when the loop variable is not updated or the condition logic is flawed.

Answer

The loop variable is incremented correctly

Answer

The loop uses a for structure

Answer

The loop body contains a break statement

Question 8

Which three of the following code snippets produce the output '5'?

Accepted Answer

System.out.println(2 + 3);. The expression `2 + 3` performs integer addition, resulting in `5`, which is then passed to `System.out.println` and printed as the string representation of the integer `5`. Option C is correct because the string literal `"5"` is printed directly. Option E is correct because the integer literal `5` is printed as its string representation.

Answer

System.out.println(2 + "3");

Answer

System.out.println("2" + 3);

Question 9

Which THREE are true about Java constructors?

Accepted Answer

A constructor cannot have a return type. Constructors in Java do not have a return type, not even void. If you attempt to add a return type to a constructor, the compiler treats it as a regular method, not a constructor, which can lead to unexpected behavior. This is a fundamental rule of Java syntax.

Answer

A constructor can be marked final

Answer

A constructor can be abstract

Question 10

A parent class has a static method display() and an instance method show(). A child class attempts to override both. What is the outcome?

Accepted Answer

Only show() can be overridden. In Java, static methods belong to the class, not instances, so they cannot be overridden—they can only be hidden. Instance methods, however, can be overridden to provide polymorphic behavior. Therefore, only the instance method show() can be overridden; display() is hidden, not overridden.

Answer

Both will be overridden

Answer

Only display() can be overridden

Answer

Neither can be overridden

Question 11

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 12

Which loop construct guarantees that the loop body executes at least once?

Accepted Answer

do-while loop. The do-while loop is the only Java loop construct that guarantees the loop body executes at least once because the condition is evaluated after the body executes. In contrast, the while and for loops evaluate the condition before the first iteration, so the body may never execute if the condition is initially false. The enhanced for loop also checks for elements before entering the body.

Answer

Enhanced for loop

Answer

while loop

Answer

for loop

Question 13

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.. In Java, arrays are objects, and when you pass an array to a method, you pass a copy of the reference to the array. This means the method can modify the contents of the array (e.g., change element values), and those changes are reflected in the original array because both the caller and the method refer to the same array object in heap memory.

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 14

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.. In Java, method overloading requires methods to have different parameter lists. While the return type can be different, it alone is not sufficient to differentiate overloaded methods; the compiler uses the method signature (name + parameter types) to resolve overloads, and return type is not part of the signature.

Answer

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

Answer

Method overloading is resolved at runtime.

Question 15

Given: int[] arr = {10,20,30}; System.out.println(arr[3]); What is the result?

Accepted Answer

ArrayIndexOutOfBoundsException. Arrays in Java are zero-indexed, so a valid index for an array of length 3 is 0, 1, or 2. Accessing index 3 is out of bounds, causing an ArrayIndexOutOfBoundsException at runtime.

Answer

30

Answer

0

Answer

NullPointerException