A field is a variable that lives inside a class. Fields store the data that each object carries. Here is a class with fields:
class Car {
String color;
int speed;
}
Every Car object created from this class will have its own color and its own speed. When you don't assign a value, Java gives fields default values: null for reference types like String, and 0 for numeric types like int.
Fields are sometimes called instance variables because each instance (object) gets its own copy.