CODEWITHSUNDEEP
javagenerics
bNd
bNd

Reputation: 7630

why generic type parameters of class allowed to cast inside class

Why compiler not stopped to write such code and throw runtime error.

public class GenericTest<T,S> {
    T x;
    S y;

    public GenericTest(T x,S y) {
        this.x=x;
        this.y=y;
    }
    void display(){
        System.out.println("Display->"+((int)x)+y); //why does it throw error runtime instead of compile time?
    }
}

When calling this will obviously failed.

public class Test {

    public static void main(String[] args) {
        GenericTest<String, String> s=new GenericTest<String, String>("Hello","World");
        s.display();

    }
}

why does it allowed to type cast for generic type:

System.out.println("Display->"+((int)x)+y);

Upvotes: 0

Views: 77

Answers (1)

sanbhat
sanbhat

Reputation: 17622

Because

GenericTest<Integer, Integer> s = new GenericTest<Integer, Integer>(new Integer(1), new Integer(2));
s.display();

is a valid code and it will produce an output.

Also T and S are unbouded generics and they are equivalent to Object. Object can be cast to Integer. 

Object o = ...;
Integer i = (Integer) o;

Further more, since Java 7, object can be cast to int. Hence there was no compilation error.

Your code is equivalent to

class GenericTest {
        Object x;
        Object y;

        public GenericTest(Object x,Object y) {
            this.x=x;
            this.y=y;
        }
        void display(){
            System.out.println("Display->"+((int)x)+y); 
        }
}

Upvotes: 3

Related Questions