Given the following piece of code:public class School{ public abstract double numberOfStudent();}which of the following statements is true?

JAVA Interfaces and Abstract Classes
Given the following piece of code:public class School{ public abstract double numberOfStudent();}which of the following statements is true?

The method numberOfStudent() in class School must have a body.

You must add a return statement in method numberOfStudent().

Class School must be defined abstract.

The keywords public and abstract cannot be used together.

The method numberOfStudent() in class School must have a body.

You must add a return statement in method numberOfStudent().

Class School must be defined abstract.

The keywords public and abstract cannot be used together.

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JAVA Interfaces and Abstract Classes
Which two of the following are legal declarations for abstract classes and interfaces?1. final abstract class Test {}2. public static interface Test {}3. final public class Test {}4. protected abstract class Test {}5. protected interface Test {}6. abstract public class Test {}

5 and 6

2 and 4

3 and 5

3 and 6

1 and 2

5 and 6

2 and 4

3 and 5

3 and 6

1 and 2

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JAVA Interfaces and Abstract Classes
Which of the following class definitions defines a legal abstract class?

class A { abstract void unfinished(); }

abstract class A { abstract void unfinished(); }

public class abstract A { abstract void unfinished(); }

class A { abstract void unfinished() { } }

class A { abstract void unfinished(); }

abstract class A { abstract void unfinished(); }

public class abstract A { abstract void unfinished(); }

class A { abstract void unfinished() { } }

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JAVA Interfaces and Abstract Classes
In Java, declaring a class abstract is useful

To force developers to extend the class not to use its capabilities.

When default implementations of some methods are not desirable.

When it doesn't make sense to have objects of that class.

When it makes sense to have objects of that class.

To prevent developers from further extending the class.

To force developers to extend the class not to use its capabilities.

When default implementations of some methods are not desirable.

When it doesn't make sense to have objects of that class.

When it makes sense to have objects of that class.

To prevent developers from further extending the class.

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JAVA Interfaces and Abstract Classes
Suppose A is an abstract class, B is a concrete subclass of A, and both A and B have a default constructor. Which of the following is correct?1. A a = new A();2. A a = new B();3. B b = new A();4. B b = new B();

2 and 3

1 and 3

3 and 4

1 and 2

2 and 4

2 and 3

1 and 3

3 and 4

1 and 2

2 and 4

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JAVA Interfaces and Abstract Classes

JAVA Interfaces and Abstract Classes Given the following piece of code:public class School{ public abstract double numberOfStudent();}which of the following statements is true?

JAVA Interfaces and Abstract Classes Which of the following class definitions defines a legal abstract class?

JAVA Interfaces and Abstract Classes In Java, declaring a class abstract is useful

JAVA Interfaces and Abstract Classes Suppose A is an abstract class, B is a concrete subclass of A, and both A and B have a default constructor. Which of the following is correct?1. A a = new A();2. A a = new B();3. B b = new A();4. B b = new B();

JAVA Interfaces and Abstract Classes Which of the following is a correct interface?

JAVA Interfaces and Abstract Classes
Given the following piece of code:public class School{ public abstract double numberOfStudent();}which of the following statements is true?

JAVA Interfaces and Abstract Classes
Which of the following class definitions defines a legal abstract class?

JAVA Interfaces and Abstract Classes
In Java, declaring a class abstract is useful

JAVA Interfaces and Abstract Classes
Suppose A is an abstract class, B is a concrete subclass of A, and both A and B have a default constructor. Which of the following is correct?1. A a = new A();2. A a = new B();3. B b = new A();4. B b = new B();

JAVA Interfaces and Abstract Classes
Which of the following is a correct interface?