/*
 * Click nbfs://nbhost/SystemFileSystem/Templates/Licenses/license-default.txt to change this license
 * Click nbfs://nbhost/SystemFileSystem/Templates/Classes/Class.java to edit this template
 */
package generics;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

/**
 *
 * @author steve
 */
public class WildCard {

    // from https://www.baeldung.com/java-generics-vs-extends-object
    public static void printListObject(List<Object> list) {
        for (Object element : list) {
            System.out.print(element + " ");
        }
    }

    public static void printListWildCard(List<?> list) {
        for (Object element : list) {
            System.out.print(element + " ");
        }
    }
    
    // A flexible copy operator for numbers
    // "PECS stands for producer-extends, consumer-super
    public static <T> void copy(List<? extends T> from, List<T> to) {
        to.clear();
        for(int i=0;i<from.size();i++)
            to.add(from.get(i));
    }

    // <T> goes after static
    // T is a comparable type
    // static <T> void foo(List<T extends Comparable<T>> foo) {} // error
    // static <T extends Comparable<T>> void foo(List<T> foo) {} // ok, but error for boos below
    static <T extends Comparable<? super T>> void foo(List<T> foo) {}
    
    static class Foo implements Comparable<Foo> {
        int n;
        @Override
        public int compareTo(Foo that) {
            return this.n - that.n;
        }
    }
    static class Boo extends Foo {}
    
    public static void main(String[] args) {
        List<Integer> data = Arrays.asList(3,4,5);
        // List<Number> lin = new ArrayList<Integer>(); // error
        List<? extends Number> lin = new ArrayList<Integer>(); // ok
        List<Object> lin2 = Arrays.asList(1,2,3);
        copy(data, lin2);

        // printListObject(lin); // error
        printListWildCard(lin);
        
        if(data instanceof List<Integer>) {} // ok
        // if(data instanceof List<Number>) {} // error
        if(lin instanceof List<? extends Number>) {} // ok
        
        // foo(lin); // error
        foo(data); // ok
        
        List<Foo> foos = new ArrayList<>();
        foos.add(new Foo());
        foo(foos);
        
        List<Boo> boos = new ArrayList<>();
        boos.add(new Boo());
        foo(boos);
    }
}