"LinkedList is not generic" error Java

Question

I'm getting an error when trying to create the linked list that says:

Exception in thread "main" java.lang.Error: Unresolved compilation problem:
The type LinkedList is not generic; it cannot be parameterized with arguments <String>
at LinkedList.main(LinkedList.java:7)

Anyone know how to fix this error? Here is the program:

import java.util.*;

public class LinkedList {
    public static void main(String[] args) {
        List<String> list = new LinkedList<String>();
        Scanner input = new Scanner(System.in);

        System.out.print("How many elements do you want to add: ");
        int num = input.nextInt();

        for(int i = 0; i < num; i++) {
            System.out.print("Add Element: ");
            String element = input.next();
            list.add(element);
        }
        System.out.println();

        System.out.println("LinkedList elements are: ");
        for(int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
    }
}

What are you trying to do? The LinkedList class that you are creating is a Java built class library in Collections. Change your classname. — S.P.
– S.P., Commented Mar 9, 2012 at 18:51

Mike Samuel · Accepted Answer · 2012-03-09 18:56:50Z

18

Change

new LinkedList<String>()

to

new java.util.LinkedList<String>()

The source of the problem is that LinkedList refers to the class containing the code class LinkedList, not java.util.LinkedList.

Unqualified class names like LinkedList (in contrast to "fully-qualified names" like java.util.LinkedList) are resolved by looking for a match in a certain order. Roughly

Look for a containing class.
Look for a non-wildcard import.
Look for a class in the same package.
Look for a wildcard import.

Section "6.5 Determining the Meaning of a Name" of the Java language specification explains in more detail.

edited Mar 9, 2012 at 18:56

answered Mar 9, 2012 at 18:50

Mike Samuel

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1 Comment

rewolf Over a year ago

I'd bet a lot that you were using Eclipse.... Eclipse loves to refer to the strangest libraries.

Adam · Accepted Answer · 2012-03-09 18:51:44Z

4

Your class is also called LinkedList so it conflicts. If you want to fix it use this line instead. Better still, just have a different name for your class...

List<String> list = new java.util.LinkedList<String>();

answered Mar 9, 2012 at 18:51

Adam

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Comments

James Montagne · Accepted Answer · 2012-03-09 18:51:35Z

3

public class LinkedList {

Your class is not defined as generic. I think though that you are trying to use Java's LinkedList, so you should rename your class.

answered Mar 9, 2012 at 18:51

James Montagne

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Comments

Adam Mihalcin · Accepted Answer · 2012-03-09 18:49:58Z

You placed your main method in a class called LinkedList, which takes precedence over the built-in LinkedList class in the compiler's name resolution algorithm. In other words, because your main method is inside a class called LinkedList, the compiler takes the name LinkedList to mean your LinkedList class instead of java.util.LinkedList. There are two easy fixes:

Rename your class
Instead of writing

List list = new LinkedList();

write

List list = new java.util.LinkedList();

I highly recommend the first option. Since your LinkedList class doesn't actually represent the linked list data structure, the name on your class is confusing to someone reading the code. Maybe call your class LinkedListTest instead i.e. your file could be

import java.util.*;

public class LinkedListTest {
    // Implementation of main and helper methods
}

Brendan Long · Accepted Answer · 2012-03-09 18:50:14Z

1

public class LinkedList {

You named your own class LinkedList, so it's taking precedence over the java.util.LinkedList.

Either change the name of the class to something else or do new java.util.LinkedList<String>() to make it explicit which one you want.

answered Mar 9, 2012 at 18:50

Brendan Long

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