The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
There are several kinds of variables:
The Bicycle
class uses the following lines of code to define its fields:
public int cadence; public int gear; public int speed;
Field declarations are composed of three components, in order:
public
or private
.The fields of Bicycle
are named cadence
, gear
, and speed
and are all of data type integer (int
). The public
keyword identifies these fields as public members, accessible by any object that can access the class.
The first (left-most) modifier used lets you control what other classes have access to a member field. For the moment, consider only public
and private
. Other access modifiers will be discussed later.
public
modifierthe field is accessible from all classes.private
modifierthe field is accessible only within its own class.In the spirit of encapsulation, it is common to make fields private. This means that they can only be directly accessed from the Bicycle class. We still need access to these values, however. This can be done indirectly by adding public methods that obtain the field values for us:
public class Bicycle { private int cadence; private int gear; private int speed; public Bicycle(int startCadence, int startSpeed, int startGear) { gear = startGear; cadence = startCadence; speed = startSpeed; } public int getCadence() { return cadence; } public void setCadence(int newValue) { cadence = newValue; } public int getGear() { return gear; } public void setGear(int newValue) { gear = newValue; } public int getSpeed() { return speed; } public void applyBrake(int decrement) { speed -= decrement; } public void speedUp(int increment) { speed += increment; } }
All variables must have a type. You can use primitive types such as int
, float
, boolean
, etc. Or you can use reference types, such as strings, arrays, or objects.
All variables, whether they are fields, local variables, or parameters, follow the same naming rules and conventions that were covered in the Language Basics lesson, VariablesNaming.
In this lesson, be aware that the same naming rules and conventions are used for method and class names, except that