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If your answer was A. Compiler Error , you were correct.

What caused the compiler error?

The compiler error was caused by the code shown in Listing 2 .

Listing 2 . The code with the problem.
public static void fillIt(Collection ref){ ref.add(0,new MyClass(4));

The problem here is that the method named fillIt receives a reference to an object of the ArrayList class as the interface type Collection , and attempts to call the following overloaded method on that reference:

add(int index, Object element)

However, the Collection interface knows nothing about a method having that signature.

Implements Collection and List

The ArrayList class implements both the Collection interface and the List interface. As you may recall from earlier modules in this series, List is a sub-interface of Collection . The List interface declares the following overloaded versions of the add method:

  • add(Object o)
  • add(int index, Object element)

The second of these two methods, which is called in Listing 2 , is unknown to the Collection interface. The Collection interface declares only the first version of the add method shown above.

Specialization

This is the result of specialization. A List object is a more-specialized collection than a Collection object.

Therefore, the version of the add method that requires two parameter cannot be called on a reference to an ArrayList object when that object is treated as the generic type Collection .

Modified program

Now, take a look at the modified version of the program as shown in Listing 3 .

What output is produced by the program shown in Listing 3 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. 44321
  • D. 4321
  • E. 1234
  • F. 12344
  • G. 443521
  • H. None of the above.
Listing 3 . The program named Comparable02.
//File Comparable02.java import java.util.*;public class Comparable02{ public static void main(String args[]){ new Worker().doIt();}//end main() }//end class Comparable02class Worker{ public void doIt(){Iterator iter; Collection ref;ref = new ArrayList(); Populator.fillIt(ref);iter = ref.iterator(); while(iter.hasNext()){System.out.print(iter.next()); }//end while loopSystem.out.println(); }//end doIt()}// end class Workerclass Populator{ public static void fillIt(Collection ref){((List)ref).add(0,new MyClass(4)); ((List)ref).add(1,new MyClass(4));((List)ref).add(2,new MyClass(3)); ((List)ref).add(3,new MyClass(2));((List)ref).add(4,new MyClass(1)); ((List)ref).add(3,new MyClass(5));}//end fillIt() }//end class populatorclass MyClass{ int data;MyClass(){ data = 0;}//end noarg constructor MyClass(int data){this.data = data; }//end parameterized constructorpublic String toString(){ return "" + data;}//end overridden toString() }//end MyClass

If your answer was G. 443521 , you are correct.

The corrected code

This version of the program illustrates a mechanism for correcting the problem in the earlier program shown in Listing 1 . The updated code that corrected the problem is shown in Listing 4 .

Listing 4 . The corrected code.
class Populator{ public static void fillIt(Collection ref){((List)ref).add(0,new MyClass(4)); ((List)ref).add(1,new MyClass(4));((List)ref).add(2,new MyClass(3)); ((List)ref).add(3,new MyClass(2));((List)ref).add(4,new MyClass(1)); ((List)ref).add(3,new MyClass(5));}//end fillIt() }//end class populator

Questions & Answers

explain and give four Example hyperbolic function
Lukman Reply
The denominator of a certain fraction is 9 more than the numerator. If 6 is added to both terms of the fraction, the value of the fraction becomes 2/3. Find the original fraction. 2. The sum of the least and greatest of 3 consecutive integers is 60. What are the valu
SABAL Reply
1. x + 6 2 -------------- = _ x + 9 + 6 3 x + 6 3 ----------- x -- (cross multiply) x + 15 2 3(x + 6) = 2(x + 15) 3x + 18 = 2x + 30 (-2x from both) x + 18 = 30 (-18 from both) x = 12 Test: 12 + 6 18 2 -------------- = --- = --- 12 + 9 + 6 27 3
Pawel
2. (x) + (x + 2) = 60 2x + 2 = 60 2x = 58 x = 29 29, 30, & 31
Pawel
ok
Ifeanyi
on number 2 question How did you got 2x +2
Ifeanyi
combine like terms. x + x + 2 is same as 2x + 2
Pawel
Mark and Don are planning to sell each of their marble collections at a garage sale. If Don has 1 more than 3 times the number of marbles Mark has, how many does each boy have to sell if the total number of marbles is 113?
mariel Reply
Mark = x,. Don = 3x + 1 x + 3x + 1 = 113 4x = 112, x = 28 Mark = 28, Don = 85, 28 + 85 = 113
Pawel
how do I set up the problem?
Harshika Reply
what is a solution set?
Harshika
find the subring of gaussian integers?
Rofiqul
hello, I am happy to help!
Shirley Reply
please can go further on polynomials quadratic
Abdullahi
hi mam
Mark
I need quadratic equation link to Alpa Beta
Abdullahi Reply
find the value of 2x=32
Felix Reply
divide by 2 on each side of the equal sign to solve for x
corri
X=16
Michael
Want to review on complex number 1.What are complex number 2.How to solve complex number problems.
Beyan
yes i wantt to review
Mark
use the y -intercept and slope to sketch the graph of the equation y=6x
Only Reply
how do we prove the quadratic formular
Seidu Reply
please help me prove quadratic formula
Darius
hello, if you have a question about Algebra 2. I may be able to help. I am an Algebra 2 Teacher
Shirley Reply
thank you help me with how to prove the quadratic equation
Seidu
may God blessed u for that. Please I want u to help me in sets.
Opoku
what is math number
Tric Reply
4
Trista
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Sidiki Reply
can you teacch how to solve that🙏
Mark
Solve for the first variable in one of the equations, then substitute the result into the other equation. Point For: (6111,4111,−411)(6111,4111,-411) Equation Form: x=6111,y=4111,z=−411x=6111,y=4111,z=-411
Brenna
(61/11,41/11,−4/11)
Brenna
x=61/11 y=41/11 z=−4/11 x=61/11 y=41/11 z=-4/11
Brenna
Need help solving this problem (2/7)^-2
Simone Reply
x+2y-z=7
Sidiki
what is the coefficient of -4×
Mehri Reply
-1
Shedrak
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
Alfred Reply
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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