Collection becomes a raw type

Question

For example we have some AbsractClass

package inherit;

import java.util.HashSet;
import java.util.Set;

/**
 * TODO: Add comment
 *
 * @author Ruslan Ibragimov
 */
public abstract class AbstractClass<T extends Integer> {

    private Set<String> strings = new HashSet<>();

    private T value;

    public Set<String> getStrings() {
        return strings;
    }

    public void setStrings(Set<String> strings) {
        this.strings = strings;
    }

    public void addString(String string) {
        strings.add(string);
    }

    public T getValue() {
        return value;
    }

    public void setValue(T value) {
        this.value = value;
    }
}

And some child:

package inherit;

/**
 * TODO: Add comment
 *
 * @author Ruslan Ibragimov
 */
public class InheritClass extends AbstractClass<Integer> {


}

Lets do simple test

package inherit;

/**
 * TODO: Add comment
 *
 * @author Ruslan Ibragimov
 */
public class TestClass {

    public static void main(String[] args) {
        TestClass testClass = new TestClass();
        testClass.test(new InheritClass());
    }

    private AbstractClass test(AbstractClass aClass) {
        for (String string : aClass.getStrings()) {
            System.out.println(string);
        }
        return aClass;
    }
}


Make output:

Error:(16, 51) java: incompatible types
required: java.lang.String
found:    java.lang.Object
for (String string : aClass.getStrings()) {

Why this happens?

I bet if you declare `AbstractClass>` with unbounded wildcard then your code will probably compile. — Meno Hochschild, Mar 26 '14 at 12:25
@Joe, no i explicitly specify the type: "private Set strings = ..." — Ruslan, Mar 26 '14 at 12:26
@MenoHochschild, right, i know that, but why i need do this. — Ruslan, Mar 26 '14 at 12:27
The raw type erases not only the generic parameter but also all other generic types so that `Set` becomes `Set`. It is explained here: [Why won't this generic java code compile?](http://stackoverflow.com/questions/662191/why-wont-this-generic-java-code-compile) — Radiodef, Mar 26 '14 at 12:36
@Radiodef yes, this is answer. Write answer, and i accept him. — Ruslan, Mar 26 '14 at 12:40
Thanks @Radiodef. I understood it now. I have taken down my answer to avoid any kind misunderstanding. — shazinltc, Mar 26 '14 at 13:02
Can you try with `private Set strings = new HashSet();` instead of `new HashSet<>();` — Wundwin Born, Mar 26 '14 at 13:44
@suninsky http://docs.oracle.com/javase/7/docs/technotes/guides/language/type-inference-generic-instance-creation.html i use jdk1.7 — Ruslan, Mar 26 '14 at 13:49

Lukino · Answer 1 · 2014-03-26T16:02:38.043

0

Instead:

private AbstractClass test(AbstractClass aClass) {

use

private AbstractClass test(AbstractClass<? extends Integer> aClass) {

which will fix compiler and if you check return value of getStrings() in code assist, you will see Set intend of Set. Could be handy also read link provided by Radiodef in comments.

edited Mar 26 '14 at 16:02

answered Mar 26 '14 at 15:57

Lukino

1,407
13
14

```AbstractClass>``` better, and this is not essence of the question. – Ruslan Mar 26 '14 at 16:23
@IRus, I though you need to fix that, that's why that answer. – Lukino Mar 26 '14 at 20:43

Collection becomes a raw type

1 Answers1