Java, Java, Java: Object-Oriented Problem Solving, 2022E

Subsection 2.8.1 Technical Terms

Subsection 2.8.2 Important Points

• Dot notation is used to refer to an object’s public elements.
• Designing a class is a matter of deciding what role it will play and what information and actions it will have.
• Writing a Java program is a matter of defining one or more classes. A class definition serves as a template for creating instance of the class.
• Classes typically contain two kinds of elements, variables and methods. An object’s state is defined by its instance variables.
• Class elements that are declared public can be accessed by other objects. Elements that are declared private are hidden from other objects.
• A class’s instance variables are usually declared private so they cannot be accessed directly by other objects.
• An object’s public instance methods can be called by other objects. Thus, they make up the object’s interface with other objects.
• Object instantiation is the process of creating an object, using the new operator in conjunction with a constructor method.
• A class definition consists of a header and a body. The header gives the class a name, specifies its accessibility (public), and its place in the Java class hierarchy (extends Object). The class body contains declarations of the class’s variables and definitions of its methods.
• By default, a newly defined class is consider a subclass of Object.
• Class elements that are declared static, such as the main() method, are associated with the class(not with its instances).
• A Java application program must contain a main() method, which is where it begins execution.
• Methods that are used solely for the internal operations of the class should be declared private.
• An instance variable declaration reserves memory for the instance variable within the object, associates a name and a type with the location, and specifies its accessibility.
• A method definition consists of two parts: a header, which names the method and provides other general information about it, and a body, which contains its executable statements.
• Declaring a variable creates a name for an object but does not create the object itself. An object is created by using the new operator and a constructor method.