Declaring classes

The following lines declare a new minimal Rectangle class in Java. The code file for the sample is included in the java_9_oop_chapter_03_01 folder, in the example03_01.java file.

class Rectangle {
}

The class keyword, followed by the class name (Rectangle), composes the header of the class definition. In this case, we don't specify a parent class or superclass for the Rectangle class. A pair of curly braces ({}) encloses the class body after the class header. In the forthcoming chapters, we will declare classes that inherit from another class, and therefore, they will have a superclass. In this case, the class body is empty. The Rectangle class is the simplest possible class we can declare in Java 9.

Note

Any new class you create that doesn't specify a superclass will be a subclass of the java.lang.Object class. Thus, the Rectangle class is a subclass of java.lang.Object.

The following lines represent an equivalent way of creating the Rectangle class. However, we...