JavaScript String and Array Methods

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Questions and Answers

What is a key advantage of using wrapper objects?

They provide advantages due to being objects (correct)
They cannot be members of ArrayLists
They can be used as primitives
They cannot be auto-unboxed

What is the purpose of inheritance?

To reuse code and create a hierarchy of classes (correct)
To provide a way to compare objects
To create a single instance of a class
To hide implementation details

What is an example of a class that can grow arbitrarily large?

BigInteger (correct)
String
Integer
ArrayList

What is a characteristic of an ArrayList?

It grows as needed (D) Signup and view all the answers

What is the term for automatically converting a primitive to a wrapper object?

Auto-boxing (C) Signup and view all the answers

What is the term for automatically converting a wrapper object to a primitive?

Auto-unboxing (D) Signup and view all the answers

How do you use the BigInteger class?

By importing the java.math package (D) Signup and view all the answers

What is the purpose of encapsulation?

To hide implementation details (B) Signup and view all the answers

What is the purpose of using the @Override annotation?

To ensure the method is overridden (A) Signup and view all the answers

What is the concept called when a sub-class object is treated as an instance of its super-class?

Upcasting (C) Signup and view all the answers

What is one of the best practices when overriding the equals() method?

Make sure a.equals(b) implies b.equals(a) (B) Signup and view all the answers

Why does upcasting work with classes?

Because a sub-class object can do everything its super-class can do (D) Signup and view all the answers

Why is inheritance useful in object-oriented programming?

To allow for code reuse and a more hierarchical organization of classes (D) Signup and view all the answers

What is polymorphism related to in object-oriented programming?

Both method overriding and method overloading (A) Signup and view all the answers

What principle ensures that functions using pointers or references to base classes can use objects of derived classes without knowing it?

Liskov Substitution Principle (C) Signup and view all the answers

What is the significance of the equals() method in Java?

It is used to compare objects for equality (A) Signup and view all the answers

What is the result of assigning a sub-class object to a super-class reference?

An implicit cast (C) Signup and view all the answers

What is the purpose of upcasting?

To allow a sub-class object to be treated as an instance of its super-class (A) Signup and view all the answers

Why is it important to follow best practices when overriding the equals() method?

So that other classes can rely on the method for correct functionality (B) Signup and view all the answers

What is an example of upcasting?

BankAccount b1 = acc; (D) Signup and view all the answers

Why is upcasting possible in object-oriented programming?

Because a sub-class is a type of its super-class (A) Signup and view all the answers

What is the relationship between the RRSP class and the BankAccount class?

RRSP is a sub-class of BankAccount (B) Signup and view all the answers

Study Notes

String and Array Methods

String methods belong to String objects.
Array methods belong to the Arrays class.

ArrayList

Follows typical object declaration syntax.
Can add as many elements as needed, and the ArrayList grows accordingly.
Very powerful, as the programmer is not responsible for basic behavior.

Auto-boxing and Auto-unboxing

Auto-boxing and auto-unboxing allow primitive types to be treated as objects.
Wrapper objects can be used like their wrapped primitives and provide advantages due to being objects, such as being members of ArrayLists.

BigInteger

Grows arbitrarily large like a Python integer.
Requires import java.math.*; to use.

Inheritance and Polymorphism

Inheritance is used to create a new class based on an existing class.
Inheritance is implemented using the "extends" keyword.

Upcasting

Upcasting: a sub-class object can be treated as an instance of its super-class.
This works because a sub-class can do everything its super-class can do.
Liskov Substitution Principle: functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it.

Downcasting

No direct mention of downcasting, but it is implied as the opposite of upcasting.

Overriding and Overloading

Overriding: a sub-class provides a specific implementation for a method already defined in its super-class.
Overloading: multiple methods with the same name but different parameters.
@Override annotation is used to ensure that the method is intended to override a super-class method.

Overriding equals()

When overriding equals(), ensure that the following hold true:
- If a.equals(b), then b.equals(a) should be true.
- If a.equals(b), and b.equals(c), then a.equals(c) should be true.
A meaningful equals method is critical, as other classes rely on it, specifically methods add() and contains() from the Collection class.