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Java Declarations and Access Control Quiz

Description: Java Declarations and Access Control Quiz
Number of Questions: 8
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Tags: java
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You want subclasses in any package to have access to members of a superclass. Which is the most restrictive access that accomplishes this objective?

java

  1. public

  2. protected

  3. private

  4. transient

Show answer
Correct Option: B
Explanation:

protected makes a member accessible only to classes in the same package or subclass of the class

What is the most restrictive access modifier that will allow members of one class to have access to members of another class in the same package?

java

  1. public

  2. abstract

  3. protected

  4. synchronized

  5. default access

Show answer
Correct Option: E
Explanation:

default access is the "package oriented" access modifier.

Which cause a compiler error?

java

  1. int[ ] scores = {3, 5, 7};

  2. int [ ][ ] scores = {2,7,6}, {9,3,45};

  3. String cats[ ] = {"Fluffy", "Spot", "Zeus"};

  4. boolean results[ ] = new boolean [] {true, false, true};

Show answer
Correct Option: B
Explanation:

To determine which option will cause a compiler error, we need to understand the syntax and rules of arrays in programming languages.

An array is a data structure that allows you to store multiple values of the same type under a single variable name. In most programming languages, arrays have a fixed size and can only store elements of the same type.

Now, let's analyze each option to identify if it will cause a compiler error:

A. int[ ] scores = {3, 5, 7}; This option is correct. It declares an integer array named "scores" and initializes it with three values: 3, 5, and 7. This code will not cause a compiler error.

B. int [ ][ ] scores = {2,7,6}, {9,3,45}; This option is incorrect. It declares a two-dimensional integer array named "scores" and initializes it with two rows and three columns. However, the array initializer is incorrect. Each row of a two-dimensional array should be enclosed in curly braces. The correct syntax should be: int [ ][ ] scores = {{2,7,6}, {9,3,45}}; The given code will cause a compiler error.

C. String cats[ ] = {"Fluffy", "Spot", "Zeus"}; This option is correct. It declares a String array named "cats" and initializes it with three strings: "Fluffy", "Spot", and "Zeus". This code will not cause a compiler error.

D. boolean results[ ] = new boolean [] {true, false, true}; This option is correct. It declares a boolean array named "results" and initializes it with three boolean values: true, false, and true. This code will not cause a compiler error.

Therefore, the option that will cause a compiler error is:

The Answer is: B

You want a class to have access to members of another class in the same package. Which is the most restrictive access that accomplishes this objective?

java

  1. public

  2. private

  3. protected

  4. default access

Show answer
Correct Option: D
Explanation:
  • Public access is the least restrictive access modifier. Members with public access can be accessed from anywhere in the program.
  • Private access is the most restrictive access modifier. Members with private access can only be accessed from within the class in which they are declared.
  • Protected access is a middle ground between public and private access. Members with protected access can be accessed from within the class in which they are declared, and from subclasses of that class.
  • Default access is also known as package-private access. Members with default access can be accessed from any class in the same package.

So, the most restrictive access modifier that allows a class in the same package to access members of another class in the same package is Default.

Here is a table that summarizes the different access modifiers in Java:

Access modifier Visibility
public Anywhere in the program
private Only within the class in which it is declared
protected Within the class in which it is declared, and from subclasses of that class
default Only within the same package

The difference between protected and default access is that protected allows access from subclasses in other packages, while default does not. For example, if you have a class Animal in package A, and a class Dog in package B that extends Animal, then the class Dog can access the protected members of Animal, but not the default members. However, if you have a class Cat in package A that extends Animal, then the class Cat can access both the protected and the default members of Animal.

Which one creates an instance of an array?
java

  1. int[ ] ia = new int[15];

  2. float fa = new float[20];

  3. char[ ] ca = "Some String";

  4. int ia[ ] [ ] = { 4, 5, 6 }, { 1,2,3 };

Show answer
Correct Option: A

Which of the following class level (nonlocal) variable declarations will not compile?

java

  1. protected int a;

  2. transient int b = 3;

  3. private synchronized int e;

  4. volatile int d;

Show answer
Correct Option: C

AI Explanation

To answer this question, we need to understand the rules and restrictions for declaring class-level (nonlocal) variables in Java.

Let's go through each option to understand why it is correct or incorrect:

Option A) protected int a; This option is correct because there are no syntax errors or restrictions with declaring a protected class-level variable in Java.

Option B) transient int b = 3; This option is correct because there are no syntax errors or restrictions with declaring a transient class-level variable in Java.

Option C) private synchronized int e; This option is incorrect because it violates the rules for declaring class-level variables. In Java, the synchronized modifier is not allowed for class-level variables. It can only be used for instance-level methods or blocks.

Option D) volatile int d; This option is correct because there are no syntax errors or restrictions with declaring a volatile class-level variable in Java.

Therefore, the correct answer is C) private synchronized int e. This option will not compile because the synchronized modifier is not allowed for class-level variables in Java.

Please select the most appropriate option.

Given a method in a protected class, what access modifier do you use to restrict access to that method to only the other members of the same class?
java

  1. final

  2. static

  3. private

  4. protected

Show answer
Correct Option: C
Explanation:

The private access modifier limits access to members of the same class.

Which is a valid declaration within an interface?

java

  1. public static short stop = 23;

  2. protected short stop = 23;

  3. transient short stop = 23;

  4. final void madness(short stop);

Show answer
Correct Option: A

AI Explanation

To answer this question, you need to understand the rules for declaring variables and methods within an interface. Let's go through each option to understand why it is correct or incorrect:

Option A) public static short stop = 23; - This option is correct. In an interface, you can declare variables with the "public static" modifiers. The variable "stop" is declared as a public static short and assigned the value 23.

Option B) protected short stop = 23; - This option is incorrect. In an interface, variables cannot have access modifiers like "protected" or "private". They are implicitly public and static.

Option C) transient short stop = 23; - This option is incorrect. In an interface, variables cannot have modifiers like "transient". They can only have "public" and "static" modifiers.

Option D) final void madness(short stop); - This option is incorrect. In an interface, you can only declare method signatures, not method implementations. The "void" return type and the presence of the method body make this option invalid.

The correct answer is Option A) public static short stop = 23;. This option is correct because it follows the rules for declaring variables within an interface.

Therefore, the correct answer is A) public static short stop = 23;

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