Inserting into a non-generic collection in java Yasser @Jobilize

Author: Yasser Ibrahim

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Question 177 / 297: What is the expected output of compiling and running the following code?

import java.util.ArrayList;
import java.util.List;

public class Test{
	public static void main(String[] args) {

		List list = new ArrayList();

		list.add("Hello");
		Foo f = new Foo();
		list.add(f); 

		f = list.get(1);
		System.out.print(list.get(0) + "-" + f);

	}
}

class Foo {
	public String toString() {
		return "Foo";
	}
}

A Hello-Foo

B compilation error

C exception at run time

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Explanation:

f = list.get(1) causes a compilation error, it must be casted to (Foo).

list is a non-generic collection, which means any type of object is allowed to be inserted in it. But because it is a non-generic collection, it means when fetching its elements, the return type of the fetched element will be Object not the actual type of the element. Therefore, we need to cast the element to its actual type.

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