Question

In: Computer Science

For Questions 1-3: consider the following code: public class A { private int number; protected String...

For Questions 1-3: consider the following code:

public class A

{

private int number;

protected String name;

public double price;

public A()

{

System.out.println(“A() called”);

}

private void foo1()

{

System.out.println(“A version of foo1() called”);

}

protected int foo2()

{

Sysem.out.println(“A version of foo2() called);

return number;

}

public String foo3()

{

System.out.println(“A version of foo3() called”);

Return “Hi”;

}

}//end class A

public class B extends A

{

private char service;

public B()

{

   super();

   System.out.println(“B() called”);

}

public void foo1()

{

System.out.println(“B version of foo1() called”);

}

protected int foo2()

{

int n = super.foo2();

System.out.println(“B version of foo2() called”);

return (n+5);

}

public String foo3()

{

String temp = super.foo3();

System.out.println(“B version of foo3()”);

return (temp+” foo3”);

}

}//end class B

public class C extends B

{

public C()

{

super();

System.out.println();

}

public void foo1()

{

System.out.println(“C version of foo1() called”);

}

}//end class C

Assignment

  1. (20 pts) What is the output of this code sequence?

B b1 = new B();

  1. (20 pts) What is the output of this code sequence?

B b3 = new B();

int n = b3.foo2();

  1. (20 pts) What is the output of the following code?

//b4 is a B object reference

System.out.println(b4.foo3());

  1. (40 pts) You coded the following class:

public class N extends String, Integer

{

}

When you compile, you get the following message:

N.java:1: ‘{‘ expected

public class N extends String, Integer

                                               ^

1 error

Explain what the problem is and how to fix it.

Solutions

Expert Solution

  1. The output will be:

A() called

B() called

Explanation:

It is given in the code that A is the superclass of B.

The constructor super() is invoked in constructor of B, hence A() is called and display on the screen and then B() is called. Therefore, constructor of B will print after the constructor of A.

  1. The output will be:

A() called

B() called

A version of foo2() called

B version of foo2() called

Explanation:

It is given in the code that A is the superclass of B.

The constructor super() is invoked in constructor of B, hence A() is called and display on the screen and then B() is called. Therefore, constructor of B will print after the constructor of A.

The foo2() method is invoked in B class. In the method of foo2(), A (superclass) is invoked which results in last two lines of output.

  1. The output will be:

A() called

B() called

A version of foo3() called

B version of foo3()

Hi foo3

Explanation:

It is given in the code that A is the superclass of B.

The constructor super() is invoked in constructor of B, hence A() is called and display on the screen and then B() is called. Therefore, constructor of B will print after the constructor of A.

Line 3 and line 4 is printed because foo3() method is called in class A and then foo3 method of class B is called.

Line 5 is printed because, A (superclass) is appended with string (“foo3”) in class B.

  1. The error is coming because, java do not allow the classes to extend from multiple super classes. In the given code, Class N trying to extend multiple class that are String and integer. Therefore, the problem is occurred.

Fixing the problem:

Include 2 super class as member in a new class. After including them, extend that new class with class N.

You can also use the interfaces in order to overcome this problem, but first method is more optimized.

venereology answered 1 month ago
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