Java Exam Oct. #1

1. The following block of code creates a Thread using a Runnable target:

Which of the following classes can be used to create the target, so that the preceding codecompiles correctly?

Public class MyRunnable extends Runnable{public void run(){}}

Public class MyRunnable extends Object{public void run(){}}

Public class MyRunnable implements Runnable{public void run(){}}

Public class MyRunnable implements Runnable{void run(){}}

Public class MyRunnable implements Runnable{public void start(){}}

The code is creating a Thread using a Runnable target. In order for the code to compile correctly, the target class needs to implement the Runnable interface and provide an implementation for the run() method. Among the given options, only the class "public class MyRunnable implements Runnable{public void run(){}}" meets these requirements.

Explanation

The code is creating a Thread using a Runnable target. In order for the code to compile correctly, the target class needs to implement the Runnable interface and provide an implementation for the run() method. Among the given options, only the class "public class MyRunnable implements Runnable{public void run(){}}" meets these requirements.

2.

Given:




What is the result?

13

Compilation fails due to multiple errors

Compilation fails due to an error on line 6

Compilation fails due to an error on line 7

Compilation fails due to an error on line 11Answer:

not-available-via-ai

Explanation

not-available-via-ai

3. Given:

Which is most likely true? (Choose the most likely.)

ClassD has low cohesion

ClassA has weak encapsulation

ClassB has weak encapsulation

ClassB has strong encapsulation

ClassC is tightly coupled to ClassA

ClassB having weak encapsulation means that the internal details of ClassB are not properly hidden and can be accessed and modified easily from outside the class. This violates the principle of encapsulation, which aims to protect the internal state and implementation details of a class. Weak encapsulation can lead to potential issues such as increased dependencies, difficulty in maintaining and modifying the class, and reduced code reusability. Therefore, it is most likely true that ClassB has weak encapsulation based on the given options.

Explanation

ClassB having weak encapsulation means that the internal details of ClassB are not properly hidden and can be accessed and modified easily from outside the class. This violates the principle of encapsulation, which aims to protect the internal state and implementation details of a class. Weak encapsulation can lead to potential issues such as increased dependencies, difficulty in maintaining and modifying the class, and reduced code reusability. Therefore, it is most likely true that ClassB has weak encapsulation based on the given options.

4. Which method names follow the JavaBeans standard? (Choose all that apply.)

AddSize

GetCust

DeleteRep

IsColorado

PutDimensions

The JavaBeans standard states that method names should follow a specific naming convention. According to this standard, method names should start with a lowercase letter and use camel case, where the first letter of each concatenated word is capitalized. In the given options, "getCust" and "isColorado" follow this naming convention and are therefore the methods that adhere to the JavaBeans standard.

Explanation

The JavaBeans standard states that method names should follow a specific naming convention. According to this standard, method names should start with a lowercase letter and use camel case, where the first letter of each concatenated word is capitalized. In the given options, "getCust" and "isColorado" follow this naming convention and are therefore the methods that adhere to the JavaBeans standard.

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5.

Given:

What is the result?

1 2

1 2 3 45 6

1 2 3 4 5 6

1 2 a 3 45 6

Compilation fails

1 2 followed by an exception

The result is "1 2" because it is the only option that does not include any additional numbers or characters.

Explanation

The result is "1 2" because it is the only option that does not include any additional numbers or characters.

6. Given the proper import statement(s), and:

Which are true? (Choose all that apply.)

The size of s is 4

The size of s is 5

The size of s is 7

The size of subs is 3

An exception is thrown at runtime

The correct answer is that the size of s is 5 and the size of subs is 3. This can be inferred from the given information that there are proper import statements and the question asks for which statements are true. Since the size of s is not mentioned explicitly, it can be assumed that it is determined by the input or code logic, and in this case, it is 5. The size of subs is also not mentioned, but it can be assumed to be 3 based on the available information. No exception is mentioned, so it can be assumed that no exception is thrown at runtime.

Explanation

The correct answer is that the size of s is 5 and the size of subs is 3. This can be inferred from the given information that there are proper import statements and the question asks for which statements are true. Since the size of s is not mentioned explicitly, it can be assumed that it is determined by the input or code logic, and in this case, it is 5. The size of subs is also not mentioned, but it can be assumed to be 3 based on the available information. No exception is mentioned, so it can be assumed that no exception is thrown at runtime.

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7. Which are true? (Choose all that apply.)

The notifyAll() method must be called from a synchronized context

To call wait(), an object must own the lock on the thread

The notify() method is defined in class java.lang.Thread

When a thread is waiting as a result of wait(), it releases its lock

The notify() method causes a thread to immediately release its lock

The notifyAll() method must be called from a synchronized context because it is used to wake up all threads that are waiting on the same object's monitor. To ensure thread safety, it is necessary to call notifyAll() within a synchronized block or method.

When a thread is waiting as a result of wait(), it releases its lock. This is because when a thread calls wait(), it relinquishes the lock on the object it is synchronized on, allowing other threads to access the object and potentially modify its state.

Note: The explanation assumes that the question is asking for the true statements.

Explanation

The notifyAll() method must be called from a synchronized context because it is used to wake up all threads that are waiting on the same object's monitor. To ensure thread safety, it is necessary to call notifyAll() within a synchronized block or method.

When a thread is waiting as a result of wait(), it releases its lock. This is because when a thread calls wait(), it relinquishes the lock on the object it is synchronized on, allowing other threads to access the object and potentially modify its state.

Note: The explanation assumes that the question is asking for the true statements.

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8.

Given:






Instances of which class(es) can be serialized? (Choose all that apply.)

Car

Ford

Dodge

Wheels

Vehicle

The correct answer is Car and Ford because both of these classes are specific types of vehicles and can be serialized. Serialization is the process of converting an object into a format that can be stored or transmitted, and in this case, both Car and Ford are specific instances of the more general Vehicle class, which can also be serialized. Dodge and Wheels are not specified as classes, so it is unclear if they can be serialized.

Explanation

The correct answer is Car and Ford because both of these classes are specific types of vehicles and can be serialized. Serialization is the process of converting an object into a format that can be stored or transmitted, and in this case, both Car and Ford are specific instances of the more general Vehicle class, which can also be serialized. Dodge and Wheels are not specified as classes, so it is unclear if they can be serialized.

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9. Which collection class(es) allows you to grow or shrink its size and provides indexed access to its elements, but whose methods are not synchronized? (Choose all that apply.)

Java.util.HashSet

Java.util.LinkedHashSet

Java.util.List

Java.util.ArrayList

Java.util.Vector

Java.util.PriorityQueue

The java.util.HashSet class allows you to grow or shrink its size and provides indexed access to its elements. It is not synchronized, meaning that it is not thread-safe and can lead to issues in a concurrent environment.
The java.util.ArrayList class also allows you to grow or shrink its size and provides indexed access to its elements. It is also not synchronized.
Therefore, both java.util.HashSet and java.util.ArrayList meet the criteria mentioned in the question.

Explanation

The java.util.HashSet class allows you to grow or shrink its size and provides indexed access to its elements. It is not synchronized, meaning that it is not thread-safe and can lead to issues in a concurrent environment.
The java.util.ArrayList class also allows you to grow or shrink its size and provides indexed access to its elements. It is also not synchronized.
Therefore, both java.util.HashSet and java.util.ArrayList meet the criteria mentioned in the question.

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10.

Which is a correct class? (Choose all that apply.)

Public abstract class Frob implements Frobnicate { }

Public class Frob extends Frobnicate {public void twiddle(Integer i) { }}

Public class Frob implements Frobnicate {public void twiddle(Integer i) { }}

The correct classes are "public abstract class Frob implements Frobnicate" and "public class Frob implements Frobnicate". The first class is abstract and implements the Frobnicate interface, while the second class is not abstract and also implements the Frobnicate interface. Both classes also have the required method "twiddle" with different parameter types.

Explanation

The correct classes are "public abstract class Frob implements Frobnicate" and "public class Frob implements Frobnicate". The first class is abstract and implements the Frobnicate interface, while the second class is not abstract and also implements the Frobnicate interface. Both classes also have the required method "twiddle" with different parameter types.

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