15.8 擦除的补偿

• new T() 无法实现，因为擦除，还因为不确定T有无参构造函数；

package chapter15._8;

public class Erased<T> {

    private final int SIZE = 100;

    public static void f(Object arg) {
        // if (arg instanceof T) {} // error
        // T var = new T(); // error
        // T[] array = new T[SIZE]; // error
        // T[] array = (T)new Object[SIZE]; // error
    }

}

package chapter15._8;

class Building {}
class House extends Building {}

public class ClassTypeCapture<T> {

    // 类型标签
    Class<T> kind;

    public ClassTypeCapture(Class<T> kind) {
        this.kind = kind;
    }

    public boolean f(Object arg) {
        // 如果arg可以转型成kind，返回true
        return kind.isInstance(arg);
    }

    public static void main(String[] args) {
        ClassTypeCapture<Building> ctt1 = new ClassTypeCapture<Building>(Building.class);
        System.out.println(ctt1.f(new Building()));
        System.out.println(ctt1.f(new House()));

        ClassTypeCapture<House> ctt2 = new ClassTypeCapture<House>(House.class);
        System.out.println(ctt2.f(new Building()));
        System.out.println(ctt2.f(new House()));
    }

}

输出

true
true
false
true