The Java(tm) FAQ -- Classes, Interfaces, and Packages

Copyright        Table of Contents        Chapters:   1   2   3   4   5   6   7   8   9   10   11

Outline

Objects, Classes, and Methods

Q1.1
What is an object?

See also: Q1.2, Q1.3, Q1.7

Q1.2
What is a class?

See also: Q1.1, Q1.3, Q1.7, Q1.12, Q1.20, Q1.32, Q2.19, JLS p. 38

Q1.3
What is a method?

See also: Q1.2, Q1.4, Q1.6, Q1.14, Q2.10

Q1.4
What is the signature of a method?

See also: Q1.13, Q1.14, Q2.24

Q1.5
What is the difference between an instance variable and a class variable?

See also: Q1.6

Q1.6
What is the difference between an instance method and a class method?

VariableExample.html

See also: Q1.2, Q1.3, Q1.5

Q1.7
How do I create an instance of a class?

See also: Q1.10, Q2.15, Q3.5, Q3.7, Q10.4, Q10.16

Q1.8
What is an abstract method?

See also: Q1.9, Q1.11

Q1.9
What is an abstract class?

See also: Q1.8, Q1.11, Q5.1

Q1.10
What is an object reference?

See also: Q2.8, JLS p. 39

Subclassing, Overloading, and Overriding

Q1.11
What is a subclass?

See also: Q1.12, Q1.25

Q1.12
What is inheritance?

See also: Q1.5, Q1.6, Q5.1

Q1.13
What is an overloaded method?

See also: Q1.2, Q1.3, Q1.4, Q1.12, Q1.14

Q1.14
What does it mean to override a method?

OverrideMethodExample.html

See also: Q1.4, Q1.12, Q1.16, Q1.17, Q2.26, Q5.1, Q8.5

Q1.15
What is the difference between overloading and overriding?

See also: Q1.13, Q1.14, Q1.16

Q1.16
Can I override the equals method or clone method from class Object to take a parameter or return a value of the type that I specify?

See also: Q1.4, Q1.13, Q1.14, Q1.15, Q2.9

Q1.17
What is the super keyword used for?

SuperExample.html

See also: Q1.11, Q1.12

Q1.18
Does the Java language provide virtual methods, like C++?

See also: Q1.10, Q1.12, Q1.14, Q1.19, Q1.26

Q1.19
What is a final class?

See also: Q1.18

Interfaces and Abstract Classes

Q1.20
What is an interface?

See also: Q1.2, Q1.21, Q1.24, JLS pp. 186–188

Q1.21
How does a class implement an interface?

See also: Q1.9, Q1.20, Q1.22, Q9.16

Q1.22
Can I instantiate an interface?

InstantiateInterfaceExample.html

See also: Q1.7, Q1.20, Q1.21

Q1.23
Why does a method in an interface appear to be public even though I didn't declare it to be public?

See also: Q1.8, Q1.20, Q1.32, JLS p. 187

Q1.24
How is an abstract class different from an interface?

See also: Q1.9, Q1.20, Q1.25

Q1.25
Does the Java language allow multiple inheritance?

See also: Q1.2, Q1.11, Q1.12, Q1.20

Q1.26
What is the instanceof keyword, and what does it do?

InstanceofExample.html

Q1.27
Why do I get the error message Can't access protected method clone... when I try to clone an object?

See also: Q1.28, Q1.33

Q1.28
How do I design a class so that it supports cloning?

CloneExample.html

See also: Q1.27, Q1.32, Q1.33

Packages and Access Modifiers

Q1.29
What are packages, and what are they used for?

See also: Q1.2, Q1.20, Q1.30, Q1.32, JLS p. 119

Q1.30
I've seen both java.applet.Applet and Applet used to refer to the Applet class -- what's the difference?

See also: Q1.29, Q1.31, JLS pp. 120ff

Q1.31
Why can I get some simple class names "for free," without using an import declaration?

See also: Q1.29, Q1.30, JLS p. 119

Q1.32
Is there a default access modifier for classes and interfaces? For class members (methods, constructors, and fields)?

See also: Q1.27, Q1.29, Q1.33

Q1.33
What does protected access mean?

See also: Q1.29, Q1.32, JLS p. 100

Q1.34
What is the accessibility of a public method or field inside a nonpublic class or interface?

See also: Q1.18, Q1.29, Q1.32