Java: Cast on Iterator ignore integer except String type

Question

Can somebody explain to me the reason why Java ignores the cast for the iterator on all object types except the String class?

I have the following code:

List list = new LinkedList();
list.add(new Object());
list.add(new String("First"));
list.add(10);
list.add(2.3);

I have two cases:

1)

Iterator<Integer> crunchifyIterator = list.iterator();
while (crunchifyIterator.hasNext()) {
    System.out.println((crunchifyIterator.next()));
}

The result is:

java.lang.Object@2a139a55
First
10
2.3

2)

Iterator<String> crunchifyIterator = list.iterator();
while (crunchifyIterator.hasNext()) {
    System.out.println((crunchifyIterator.next()));
}

The result is:

Exception in thread "main" java.lang.ClassCastException: java.lang.Object cannot be cast to java.lang.String

I don't know what the reason is.

cyroxis · Accepted Answer · 2016-06-14 16:31:34Z

6

There are multiple versions of System.out.println()

You are adding different types of Objects to the list

List list = new LinkedList();
list.add(new Object()); // Type Object
list.add(new String("First")); // Type String
list.add(10);  // Type Integer (not int)
list.add(2.3); // Type Float (not float)

In the fist loop it calls

System.out.println(Object o);  // String, Interger, Float are all objects this causes no issues

In the second loop it calls

System.out.println(String str);  // This is where the casting fails, Object, Integer, and Float are not Strings.

The reason for this is in operator overloading the version called is determined at compile time (not runtime).

Note:

In practice you should not be using a generic type on your iterator other then the generic type of your List. In your case the type defaults to Object.

edited Jun 14, 2016 at 16:31

answered Jun 14, 2016 at 16:13

cyroxis

3,72124 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Abelo Over a year ago

Hi cyroxis, but if I write this Iterator<Integer> crunchifyIterator = list.iterator(); is permited and if I try whit that Iterator<String> crunchifyIterator = list.iterator(); throws a exception

cyroxis Over a year ago

@Abelo I updated my answer to give some more clarity.

Collectives™ on Stack Overflow

Java: Cast on Iterator ignore integer except String type

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related