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The Java Interview Handbook: 300+ Interview Questions

Generic Types

Explore how Java generics impact the creation and type safety of arrays, focusing on type erasure, covariance, and casting issues. Understand why direct generic array creation fails and how reflection provides a correct approach for creating generic arrays safely.

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1.

Explain generic types?

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Java
class Demonstration {
    public static void main( String args[] ) {
      (new Printer<Integer>()).print(Integer.valueOf(555));
      (new Printer<String>()).print("print away");
      (new Printer<Object>()).print(new Demonstration());
        
    }
}
class Printer<T> {
    void print(T t) {
        System.out.println("printing : " + t.toString());
    }
}
1.

What are generic methods?

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1 / 4
Java
class Demonstration {
    public static void main( String args[] ) {
        // Attempt to create a generic array
        // results in a ClassCastException
        String[] array = Demonstration.<String>createArray(5);
    }
    static <T> T[] createArray(int size) {
        T[] array = (T[]) new Object[size];
        return array;
    }
}

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