Generic Programming in Java

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Questions and Answers

What will be the output of the following code snippet: public class DemoClass { static void DemoMethod(int...v) { for (int i: v) System.out.print(i + " "); } public static void main(String args[]) { DemoMethod(9, 5, 4); DemoMethod(7); } }?

9 5 4 7 (correct)
9 5 47
Run-time error
Compile-time error

Which symbol is identified as a wildcard in Java generic programming?

%
? (correct)
&
!

Which keyword is necessary to declare an upper bounded wildcard in Java?

extends (correct)
super
bound
implement

What is the main advantage of using generic programming in Java?

It allows for creating reusable and type-safe code. (A) Signup and view all the answers

In Java generics, how can primitive types be used as type arguments?

They need to be wrapped in their corresponding wrapper classes. (B) Signup and view all the answers

Which operator is commonly associated with defining generic types in Java?

<> (B) Signup and view all the answers

What mechanism in Java generics allows for removing type parameters in compiled code?

Type erasure (A) Signup and view all the answers

In the provided code example, what data type is the printArray method designed to accept?

Any object type (B) Signup and view all the answers

When using varargs in a method, what type of variables can be passed?

Zero or more parameters of the declared type (A) Signup and view all the answers

What is the result of using a wildcard '?' in generics?

It acts as a placeholder for any type. (C) Signup and view all the answers

What will happen if you try to pass a String array to the printArray method defined in the code?

It will print the String elements correctly. (A) Signup and view all the answers

What happens if a method is called with a varying number of arguments in Java?

The method can handle the arguments as an array. (C) Signup and view all the answers

When using generic programming, what does type safety refer to?

Preventing runtime errors by enforcing type constraints. (A) Signup and view all the answers

What output will the provided code produce when executed?

5 4 3 2 1 (B) Signup and view all the answers

Which of the following is a potential downside of using generics in Java?

They prevent the use of primitive data types. (C) Signup and view all the answers

What will happen if the method printArray tries to print an array of objects not supporting toString?

It will call the superclass toString method. (B) Signup and view all the answers

What does type erasure in Java generics refer to?

The process of automatically converting generic types to their raw types during compilation. (A) Signup and view all the answers

Which statement is true regarding the benefits of using generics in Java?

Generics allow the same code to work for different types of data. (C) Signup and view all the answers

What will happen if you pass a String object into a generic class expecting a Number?

The code will not compile due to a type mismatch error. (B) Signup and view all the answers

In the context of generics, what is a primary role of the Java compiler?

To enforce tighter type checks on generic code at compile time. (D) Signup and view all the answers

In a generic method, which of the following is a consequence of using generics?

Code can be reused for multiple types without rewriting. (B) Signup and view all the answers

What is the expected behavior of the square function if a non-numeric type is used with MyGenericClass?

It will not compile due to a type mismatch error. (D) Signup and view all the answers

Which of the following is a characteristic feature of generics?

Generics allow for the creation of type-safe collections. (D) Signup and view all the answers

How does type erasure impact generic types during execution?

Generic types are removed, leaving only raw types. (D) Signup and view all the answers

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Study Notes

What is Generic Programming in Java?

Generic Programming in Java is a programming paradigm that allows creating reusable code.
It enables defining classes and methods that can work with different types while maintaining type safety.

Generic Type Symbol

The diamond operator <> denotes a generic type in Java.
It is used when declaring and instantiating generic classes or invoking generic methods.

How Does Generic Programming Work?

Generic methods like printArray can accept an array of any data type as input and print it.
Varargs methods use the ellipsis ... to accept zero or more parameters.

Wildcard Symbol

The question mark symbol ? is a wildcard in generic programming in Java.

Upper Bounded Wildcard

The keyword extends is used to declare an upper-bounded wildcard in generic programming.
Example: methodUBA(? extends A) { … }

Primitive Types & Generics

Primitive types cannot be directly used as type arguments in generic programming.
They need to be wrapped in their corresponding wrapper classes, such as Integer for int, Double for double, etc.

Type Erasure

Type erasure happens during compilation when the compiler replaces the type parameters with their raw types.
This ensures backward compatibility with older versions of Java that did not support generics.

Advantages of Generics:

The Java compiler performs stricter type checks on generic code at compile time.
Generics allow programming with types as parameters, making code more flexible and reusable.
Generics enable implementing generic algorithms that can work with various data types.

Code Example and Error

The example code snippet defines the MyGenericClass with T extending the Number class.
An error occurs during compilation because T is restricted to types that extend Number.
Trying to instantiate MyGenericClass with String causes a type mismatch error.