CODEWITHSUNDEEP
javagenericsarraylistbounds
hasNoPatience
hasNoPatience

Reputation: 79

Java Generics - Unexpected bounds

No Problems here

public class MyList<E extends Number> extends ArrayList<E> {
}

.

Unexcepted bound. What does this mean? And why is it wrong? Thanks for help.

public class MyList<E extends Number> extends ArrayList<E extends Number> {

}

Upvotes: 2

Views: 4819

Answers (2)

Tushar J Dudhatra
Tushar J Dudhatra

Reputation: 353

public class MyList<E extends Number> extends ArrayList<E> {
    private static final long serialVersionUID = -1025575227555594680L;

}

This should work with no compilation error and no warnings even. Let me know if you still have the same error.

Upvotes: 2

rrobby86
rrobby86

Reputation: 1484

class MyList<E extends Number> is OK because you declare a type parameter, so you have to give it a name (E) and you can optionally declare it as bounded (extends Number).

In extends ArrayList<E> instead you just have to "use" a type parameter: with "<E>" you refer to the parameter declared in your class, for which a bound is already given in its declaration. "<? extends Number>" (with ? in place of E) would also be accepted by the compiler (although it would be not what you want). Instead, "<E extends Number>" is taken as a type parameter declaration, so it is a compile error.

Upvotes: 7

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