Question

I am practicing programming with generic classes. I want to implement a class for a list element that holds a reference on an object of generic type and a reference on the next list element.

So I came up with this class:

class List<T>{
    T val;
    List next:
}

How would you define the constructor for this class? Any other advice to understand generic classes and their use?

Answer 1

you can leave it with default constructor and then use it List<String> list = new List<String>(); – now val in your class will be String. Another way:

public class List<T>{
    T val;
    List<T> next;

    public List(T val, List<T> next) {
        this.val = val;
        this.next = next;
    };

    public T getVal() {
        return val;
    }
}

And then you can use it this way:

List<String> strList = new List<String>("test", null);
System.out.println( strList.getVal() );

as result “test” should be printed

As for advice, I think the best thing is to read this book: Java Generics and Collections
it contains good description and a lot of examples how to use it.