// generics/GenericReading.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
import java.util.*;

public class GenericReading {
 static List<Apple> apples =
 Arrays.asList(new Apple());
 static List<Fruit> fruit = Arrays.asList(new Fruit());
 static <T> T readExact(List<T> list) {
 return list.get(0);
 }
 // A static method adapts to each call:
 static void f1() {
 Apple a = readExact(apples);
 Fruit f = readExact(fruit);
 f = readExact(apples);
 }
 // A class type is established
 // when the class is instantiated:
 static class Reader<T> {
 T readExact(List<T> list) { return list.get(0); }
 }
 static void f2() {
 Reader<Fruit> fruitReader = new Reader<>();
 Fruit f = fruitReader.readExact(fruit);
 //- Fruit a = fruitReader.readExact(apples);
 // error: incompatible types: List<Apple>
 // cannot be converted to List<Fruit>
 }
 static class CovariantReader<T> {
 T readCovariant(List<? extends T> list) {
 return list.get(0);
 }
 }
 static void f3() {
 CovariantReader<Fruit> fruitReader =
 new CovariantReader<>();
 Fruit f = fruitReader.readCovariant(fruit);
 Fruit a = fruitReader.readCovariant(apples);
 }
 public static void main(String[] args) {
 f1(); f2(); f3();
 }
}