JAVA: Nesting in Iterator in a public class

Question

So for a school project, I need to make a private method that implements the Iterator interface. I have my method SetIterator, and it looks like this:

  private class SetIterator implements Iterator<T> {
  private T[] items; 
  private int count; 
  private int current; 

  private SetIterator(T[] elements, int size) {
     items = elements;
     count = size;
     current = 0;
  }

  private boolean hasNext() {
     return (current < count);
  }

  private T next() {
     if (!hasNext()) {
        throw new NoSuchElementException();
     }

     return items[current++];
  }

However, I am not able to compile because I'm getting this error message:

ArraySet.java:311: error: next() in ArraySet.SetIterator cannot implement next() in Iterator
  private T next() {
            ^
attempting to assign weaker access privileges; was public
where T,E are type-variables:
T extends Comparable<? super T> declared in class ArraySet
E extends Object declared in interface Iterator
ArraySet.java:307: error: hasNext() in ArraySet.SetIterator cannot implement hasNext() in Iterator
private boolean hasNext() {
                  ^
attempting to assign weaker access privileges; was public

I've never really run into this before, so any help would be greatly appreciated.

Make next() public: public T next() {.

Gábor Bakos
– Gábor Bakos

2015-02-27 08:47:13 +00:00
Commented Feb 27, 2015 at 8:47 — Gábor Bakos
– Gábor Bakos, Commented Feb 27, 2015 at 8:47

Arnaud Denoyelle · Accepted Answer · 2015-02-27 08:47:06Z

2

Iterator is an interface. Hence, its methods are public. You cannot implement the method and make it private.

Change the visibility to public.

public boolean hasNext() {
  return (current < count);
}

answered Feb 27, 2015 at 8:47

Arnaud Denoyelle

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1 Comment

gigadude7 Over a year ago

I guess I just figured that having a public method in a private class would violate encapsulation somehow. Thanks :D

assylias · Accepted Answer · 2015-02-27 08:47:11Z

2

The error is fairly self explanatory: next and hasNext are public in Iterator so you can't make them private. Change private to public and the error should go away.

answered Feb 27, 2015 at 8:47

assylias

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Comments

divesh premdeep · Accepted Answer · 2015-02-27 08:51:45Z

The reason you're getting this error is because you cannot assign a "weaker" privilege to a method you override from a super class or implement from an interface.

Since methods defined on an interface in Java are public by default, the Java compiler prevents us from implementing these methods with a weaker access privilege such as protected or private. The reason it does so is because of an inherent principle of object oriented programming - an instance of a subclass should be generally usable where an instance of its super class is expected (checkout the Liskov Substitution Principle to get a better understanding of this concept).

To sum up, declare SetIterator's hasNext() and next() methods as public, since they implement the Iterator interface's methods.

Andy · Accepted Answer · 2015-02-27 08:54:55Z

0

you would not have encountered this Issue if you would have known the rules for Overrding inr Java .

Try to google on overriding rules in Java. start from here : http://java67.blogspot.com/2012/09/what-is-rules-of-overloading-and-overriding-in-java.html

Always remember the thumb rule : Never reduce the scope of method , you can always increase the scope of method while overriding it , but can never decerese it.

answered Feb 27, 2015 at 8:54

Andy

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