Question

What output is produced by the following code? Explain how it works (at least 5 lines).

class Super {
int num = 1;
int id = 2;
}

class Sub extends Super {
int num = 3;

public void display() {
System.out.println(num);
System.out.println(super.num);
System.out.println(id);
}
}

public class Inheritance1 {
public static void main (String[] args) {
Sub obj = new Sub();
obj.display();
}
}

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Example of "Explain how it works"

Sample Question:
What output is produced by the following code?   Explain how it works.

class student {

    String name;

    int age;

}

public class q6_ArryList1 {

public static void main(String args[]) {

      ArrayList<student>myArray = new ArrayList<>();

       for(int i=0; i< 4; i++){

         student s = new student();      

         s.name="Emily"+i;

         myArray.add(s);  

      }

    for (int i = 0; i<myArray.size(); i++){

        System.out.format("%s %n", myArray.get(i).name, myArray.get(i).age);

     }

    System.out.println();

    for (int i = 0; i<myArray.size(); i++){

       if (i % 2 ==0) {

        myArray.remove(1); }

    }

   for (int i = 0; i<myArray.size(); i++){

     System.out.format("%s %n", myArray.get(i).name, myArray.get(i).age);

    }

}

}

Answer:

Emily 0
Emily 1
Emily 2
Emily 3
Emily 0
Emily 3

How it works:
In this problem, an arrayList is created, then Emily + i is added to the arrayList where i is the for loop variable. The for loop goes from 0 inclusive to 4 exclusive. Therefore the arrayList contains [Emily0,Emily1, Emily2, Emily3]. After this, another for loop that goes through the arrayList is executed. An if statement inside the for loop gives a condition that if i %2 = 0, then remove the value at position 1. Thus, at 0, index 1 which is Emily1 is removed. At 1, nothing is removed. At 2, Emily2 is removed. Lastly, the arrayList, which contains[Emily0 and Emily3] is printed.

Answer 1

Question :

Answer :

3

1

2

How it works:

• Given code snippet contains base class with name Super with two public integer variables num and id
• These variables are assigned with value num=1 and id=2
• Then there is one sub class called Sub which extends base class Super.
• These Sub class contains integer variable num=3
• Then sub class contains display() method which is public
• This display() method print value of num using
• System.out.println(num); which refers to the value of variable num declared in the Sub class hence num=3
• Then statement System.out.println(super.num); will print the value of the num from base class Super.
• Here super is a keyword which is used to refer to the variable from the Super class.
• Note here super is keyword and Super is class
• Then a driver class is created with main() method
• In the main() method object of Sub class is created with name obj and then display method is called using obj.
• Hence output is 3 1 2
• Below screen shows the output