Java Object Casting and Comparison Quiz

Object-Oriented Programming Concepts

• Casting objects: explicit casting is necessary when assigning a subclass object to a superclass variable.
• The equals method checks if two object variables have the same value, not the same reference.

Access Modifiers

• public: accessible from anywhere
• protected: accessible from the same class, subclasses, and same package
• default: accessible from the same class and same package
• private: accessible only from the same class

The final Modifier

• A final class cannot be extended.
• A final variable is a constant.
• A final method cannot be overridden by its subclasses.

Exceptions

• A disruptive event that happens during program execution.

Class Abstraction and Relationships

• Class abstraction: separating class implementation from its use.
• Class relationships: association, aggregation, composition, and inheritance.

The String Class

• Interned strings: saved in memory to avoid duplication.
• Matching, replacing, and splitting patterns using regular expressions.

Inheritance and Polymorphism

• Inheritance: a subclass inherits properties from a superclass.
• Polymorphism: a variable of a supertype can refer to a subtype object.
• Dynamic binding: JVM searches for the correct method implementation during runtime.

File Input/Output

• The File class provides an abstraction of system files and deals with machine-dependent complexities.
• PrintWriter is used to write data to a file.
• Scanner is used to read data from a file.

Reading Data from the Web

• The URL class is used to read data from the internet.
• Scanner can be used to read data from the web, but it has a small buffer size and is inefficient.