A computer is a machine that follows a list of instructions called a program. An Android device is a computer and an app is a program. Inside an Android device, a variable is a container that holds a value such as a number or a piece of text. An object is a big variable that can contain smaller variables inside of it. Attached to an an object we can have lists of instructions—in effect, little programs—called methods. There are many classes (types) of objects.

The screen of an Android app is made up of rectangular areas called Views. For example, a checkbox is a touch-sensitive View that looks and acts like a checkbox: we can tap it to check and uncheck it. See Checkbox in the Material Design spec, and the Checkboxes Guide.

Each View is drawn on the screen by a corresponding Java object. For example, a checkbox is drawn by an object of class CheckBox. In fact, the Java object is the real checkbox. But when talking about what the user sees, it’s convenient to refer to the rectangular area on the screen as the "checkbox".

A CheckBox object has a method named isChecked() that returns true or false to indicate whether the box is currently checked.