Accessing an object's methods while using List Iterator

Question

My objective is to iterate over a list of objects, and have the two functionalities: - be able to remove from the list during iteration. - be able to access the public get methods of the objects I'm iterating over, to be able to determine whether or not they should be removed.

For example, how would I get the following to work? Currently it gives the exception java.util.ArrayList$Itr cannot be cast to random.folder.dir.TestClass.

public class TestClass {
    public int foo;

    public TestClass(int foo) {
        this.foo = foo;
    }

    public int getFoo() {
        return foo;
    }       
}




List<TestClass> testList = new ArrayList<TestClass>();
testList.add(new TestClass(1));
testList.add(new TestClass(2));
testList.add(new TestClass(3));

Iterator<TestClass> it = tickScratch.iterator();
while(it.hasNext()) {
    if(((TestClass)it).getFoo() == 2)
        it.remove();
}

Jack · Accepted Answer · 2013-11-19 03:45:07Z

3

it is a ListIterator<TestClass> instance, hence it doesn't have the getFoo() method.

You should use next() to fetch the next element and then remove it if needed:

while (it.hasNext() {
  TestClass current = it.next(); 

  if (current.getFoo() == 2)
    it.remove();
}

answered Nov 19, 2013 at 3:45

Jack

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1 Comment

user2763361 Over a year ago

Does this work if I want to change the internal state of the object inside the list while in the loop (through setter methods)?

Prabhakaran Ramaswamy · Accepted Answer · 2013-11-19 03:43:25Z

1

Need change

  if(((TestClass)it).getFoo() == 2)

to

    if(it.getNext().getFoo() == 2)

answered Nov 19, 2013 at 3:43

Prabhakaran Ramaswamy

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1 Comment

Ron Over a year ago

you can't call getFoo() on an Iterator

Ron · Accepted Answer · 2013-11-19 03:43:09Z

0

You have a problem in your code here:

Iterator<TestClass> it = tickScratch.iterator();
while(it.hasNext()) {
    if(((TestClass)it).getFoo() == 2)
        it.remove();
}

it is an Iterator<TestClass> not a TestClass, therefore you are getting an error that $Itr cannot be cast to random.folder.dir.TestClass. What you are doing is similar to casting an ArrayList<String> to a String, you have a bunch of TestClass objects, not just one.

Use an iterator like this:

Iterator<TestClass> it = tickScratch.iterator();
while(it.hasNext()) {
    if(it.next().getFoo() == 2)
        it.remove();
}

answered Nov 19, 2013 at 3:43

Ron

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Comments

frozenkoi · Accepted Answer · 2013-11-19 03:45:46Z

0

The next () funcion returns the object 'pointed to' by the iterator. Use it as you wish.

http://docs.oracle.com/javase/7/docs/api/java/util/Iterator.html#next()

answered Nov 19, 2013 at 3:45

frozenkoi

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