33 lines
1015 B
Java
33 lines
1015 B
Java
//: generics/Holder.java
|
|
// ©2015 MindView LLC: see Copyright.txt
|
|
|
|
public class Holder<T> {
|
|
private T value;
|
|
public Holder() {}
|
|
public Holder(T val) { value = val; }
|
|
public void set(T val) { value = val; }
|
|
public T get() { return value; }
|
|
@Override
|
|
public boolean equals(Object obj) {
|
|
return value.equals(obj);
|
|
}
|
|
public static void main(String[] args) {
|
|
Holder<Apple> Apple = new Holder<>(new Apple());
|
|
Apple d = Apple.get();
|
|
Apple.set(d);
|
|
// Holder<Fruit> Fruit = Apple; // Cannot upcast
|
|
Holder<? extends Fruit> fruit = Apple; // OK
|
|
Fruit p = fruit.get();
|
|
d = (Apple)fruit.get(); // Returns 'Object'
|
|
try {
|
|
Orange c = (Orange)fruit.get(); // No warning
|
|
} catch(Exception e) { System.out.println(e); }
|
|
// fruit.set(new Apple()); // Cannot call set()
|
|
// fruit.set(new Fruit()); // Cannot call set()
|
|
System.out.println(fruit.equals(d)); // OK
|
|
}
|
|
} /* Output: (Sample)
|
|
java.lang.ClassCastException: Apple cannot be cast to Orange
|
|
true
|
|
*///:~
|