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Generics Quiz 2

The quiz below tests your knowledge of the material learnt in Generics - Lesson 2 - Raw/Generic Type Comparison.

Question 1 : What will the compiler do with the following code  private static final List names = new ArrayList();
- The code compiles but with warning messages for raw types and unchecked calls.
Question 2 : Which is the preferred syntax?
- <code>private static final List<String> names = new ArrayList<>();</code> is preferred as it uses the diamond operator which answer B does not. Answer C uses a raw type and is unsafe.
Question 3 : What happens when we try to compile the following class?
package info.java8;
import java.util.*;

public class RawTypeNameCollection {
    private static final List<String> names = new ArrayList<>();

    public static void main (String[] args) {
        names.add("Bill");
        names.add("Ben");
        names.add(6);
    }
}
- The code will not compile as the compiler stops the <code>int</code> from being put into the <code>String</code> collection.
Question 4 : We can mix raw types and generics
- We CAN mix raw types and generics although this is in no way recommended as it can lead to unsafe code and runtime exceptions.
Question 5 : What happens when we try to compile the following class?
package info.java8;
import java.util.*;

public class RawTypeNameCollection {
    private static final List<String> names = new ArrayList<>();

    public static void main (String[] args) {
        names.add("Bill");
        names.add("Ben");
        names.add("6");
    }
}
- The code compiles normally as we are just putting <code>String</code> objects into a <code>String</code> collection.
Question 6 : Which of the following syntax will compile?
private static final List<String> names = new ArrayList<>(); //1

private static final List<String> names = new ArrayList<String>(); //2

private static final List<String> names = new ArrayList(); //3
- All the syntax is valid although answer B does not use the diamond operator and answer C uses a raw type and is unsafe.
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What's Next?

In the next quiz we test your knowledge of generic interfaces.