CODEWITHSUNDEEP
javagenericscompiler-errors
fastcodejava
fastcodejava

Reputation: 41117

Cannot convert from java.lang.Class<T> to java.lang.Class<T>

I'm having this problem. Shouldn't the constructor have the same type parameters as the class?

public class MyBuilder<T> {

private final Class<T> clss;

/**
 *
 * @param clss
 */
public <T> MyBuilder(final Class<T> clss) {
    this.clss = (Class<T>) clss; // compiler error here
}


Type mismatch: cannot convert from java.lang.Class<T> to java.lang.Class<T>

If I remove the <T> for the ctor it compiles, but I cannot do :

MyBuilder<Foo> myBuilder = new MyBuilder<Foo>();   // compiler error here

The error is The constructor MyBuilder<Foo>() is undefined.

Upvotes: 1

Views: 3503

Answers (2)

Paul Bellora
Paul Bellora

Reputation: 55233

Remove the type parameter from the constructor, as well as the cast:

public MyBuilder(final Class<T> clss) {
   this.clss = clss;
}

The type parameters of a class, T in this case, are implicitly declared for any instance members, including constructors. By explicitly declaring T for the constructor you were actually masking the T declared by the class, causing that confusing error.

Upvotes: 8

勿绮语
勿绮语

Reputation: 9330

Because this "T" is not that "T". T is just a "place holder" for some type. The T in 

private final Class<T> clss;

is unrelated to the T in the constructor parameter.

Upvotes: 5

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