在泛型类中为数组列表实现Add方法

Question

I keep getting an error telling me that add(T) is undefined for the type T when trying to add add :

package p07;
import java.util.ArrayList;

public class MyList<T extends Number>
{
    private T ArrayList;

    public MyList(T ArrayList)
    {
        this.ArrayList=ArrayList;
    }
    public void add(T x)
    {
        ArrayList.add(x);
    }
}

Any advice on how to proceed?

Answer 1

You've incorrectly made the ArrayList a variable of type T . The line private T ArrayList; should be private ArrayList<T> l; where l would be the variable name.

The issue is that ArrayList is a generic type, so when you pass your generic type to it, you must pass it through ArrayList<T> . T ArrayList is a variable called ArrayList of type T .

You have to change this everywhere: every T you've shown in this snippet should be an ArrayList<T> .