Question

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.

Answer 1

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.