Type Bounds and Wildcards
Suppose you want to be able to assume a type parameter is a subtype of a given type. How do you do this?
<T extends Comparable<T>>
restricts the type specified as being a subtype of Comaprable, which means it implements the Comparable<T> interface. Here is a class with a static method that takes advantage of this.
import java.util.List;
import java.util.ArrayList;
public class Order
{
public static <T extends Comparable<T>> boolean isInOrder(List<T> list)
{
int n = list.size();
for(int k = 0; k < n - 1; k++)
{
if( list.get(k).compareTo(list.get(k+1)) > 0)
{
return false;
}
}
return true;
}
public static void main(String[] args)
{
List<String> st = new ArrayList<>();
st.addAll(List.of("a", "c", "b"));
//yields a false
System.out.println("isInOrder(st) = " + isInOrder(st));
st.clear();
//yields a true
st.addAll(List.of("a", "b", "c"));
System.out.println("isInOrder(st) = " + isInOrder(st));
}
}
Function-Like Objects and Streams
forEach
This is a default method of the
Iteratable<T> interface.
What is Consumer< ? super T
t?
Dang. Type bounds again. Let's break it down. Firstly, Consumer<T>
is a generic functional interface. It's one specified method is
void accept(T t)
So it peforms some action on an object of type T
that does not have
any return value.