Access modifier private java

Содержание

Java — Access Modifiers
Example
Private Access Modifier — Private
Example
Public Access Modifier — Public
Example
Protected Access Modifier — Protected
Example
Access Control and Inheritance
Controlling Access to Members of a Class
Модификатор доступа (Access modifiers) в Java
1- Modifier в Java
2- Обзор access modifier
3- private access modifier
4- private constructor
5- Access modifier по умолчанию
6- protected access modifier
7- public access modifier
8- Метод переопределения
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Access modifier private java

Java — Access Modifiers

Default access modifier means we do not explicitly declare an access modifier for a class, field, method, etc.

A variable or method declared without any access control modifier is available to any other class in the same package. The fields in an interface are implicitly public static final and the methods in an interface are by default public.

Example

Variables and methods can be declared without any modifiers, as in the following examples −

String version = «1.5.1»; boolean processOrder()

Private Access Modifier — Private

Methods, variables, and constructors that are declared private can only be accessed within the declared class itself.

Private access modifier is the most restrictive access level. Class and interfaces cannot be private.

Variables that are declared private can be accessed outside the class, if public getter methods are present in the class.

Using the private modifier is the main way that an object encapsulates itself and hides data from the outside world.

Example

The following class uses private access control −

public class Logger < private String format; public String getFormat() < return this.format; >public void setFormat(String format) < this.format = format; >>

Here, the format variable of the Logger class is private, so there’s no way for other classes to retrieve or set its value directly.

So, to make this variable available to the outside world, we defined two public methods: getFormat(), which returns the value of format, and setFormat(String), which sets its value.

Public Access Modifier — Public

A class, method, constructor, interface, etc. declared public can be accessed from any other class. Therefore, fields, methods, blocks declared inside a public class can be accessed from any class belonging to the Java Universe.

However, if the public class we are trying to access is in a different package, then the public class still needs to be imported. Because of class inheritance, all public methods and variables of a class are inherited by its subclasses.

Example

The following function uses public access control −

public static void main(String[] arguments) < // . >

The main() method of an application has to be public. Otherwise, it could not be called by a Java interpreter (such as java) to run the class.

Protected Access Modifier — Protected

Variables, methods, and constructors, which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members’ class.

The protected access modifier cannot be applied to class and interfaces. Methods, fields can be declared protected, however methods and fields in a interface cannot be declared protected.

Protected access gives the subclass a chance to use the helper method or variable, while preventing a nonrelated class from trying to use it.

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Example

The following parent class uses protected access control, to allow its child class override openSpeaker() method −

class AudioPlayer < protected boolean openSpeaker(Speaker sp) < // implementation details >> class StreamingAudioPlayer extends AudioPlayer < boolean openSpeaker(Speaker sp) < // implementation details >>

Here, if we define openSpeaker() method as private, then it would not be accessible from any other class other than AudioPlayer. If we define it as public, then it would become accessible to all the outside world. But our intention is to expose this method to its subclass only, that’s why we have used protected modifier.

Access Control and Inheritance

The following rules for inherited methods are enforced −

Methods declared public in a superclass also must be public in all subclasses.
Methods declared protected in a superclass must either be protected or public in subclasses; they cannot be private.
Methods declared private are not inherited at all, so there is no rule for them.

Источник

Controlling Access to Members of a Class

Access level modifiers determine whether other classes can use a particular field or invoke a particular method. There are two levels of access control:

At the top level public , or package-private (no explicit modifier).
At the member level public , private , protected , or package-private (no explicit modifier).

A class may be declared with the modifier public , in which case that class is visible to all classes everywhere. If a class has no modifier (the default, also known as package-private), it is visible only within its own package (packages are named groups of related classes you will learn about them in a later lesson.)

At the member level, you can also use the public modifier or no modifier (package-private) just as with top-level classes, and with the same meaning. For members, there are two additional access modifiers: private and protected . The private modifier specifies that the member can only be accessed in its own class. The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package.

The following table shows the access to members permitted by each modifier.

Access Levels

Modifier	Class	Package	Subclass	World
public	Y	Y	Y	Y
protected	Y	Y	Y	N
no modifier	Y	Y	N	N
private	Y	N	N	N

The first data column indicates whether the class itself has access to the member defined by the access level. As you can see, a class always has access to its own members. The second column indicates whether classes in the same package as the class (regardless of their parentage) have access to the member. The third column indicates whether subclasses of the class declared outside this package have access to the member. The fourth column indicates whether all classes have access to the member.

Access levels affect you in two ways. First, when you use classes that come from another source, such as the classes in the Java platform, access levels determine which members of those classes your own classes can use. Second, when you write a class, you need to decide what access level every member variable and every method in your class should have.

Let’s look at a collection of classes and see how access levels affect visibility. The following figure shows the four classes in this example and how they are related.

Classes and Packages of the Example Used to Illustrate Access Levels

The following table shows where the members of the Alpha class are visible for each of the access modifiers that can be applied to them.

Visibility

Modifier	Alpha	Beta	Alphasub	Gamma
public	Y	Y	Y	Y
protected	Y	Y	Y	N
no modifier	Y	Y	N	N
private	Y	N	N	N

If other programmers use your class, you want to ensure that errors from misuse cannot happen. Access levels can help you do this.

Use the most restrictive access level that makes sense for a particular member. Use private unless you have a good reason not to.
Avoid public fields except for constants. (Many of the examples in the tutorial use public fields. This may help to illustrate some points concisely, but is not recommended for production code.) Public fields tend to link you to a particular implementation and limit your flexibility in changing your code.

Источник

Модификатор доступа (Access modifiers) в Java

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1- Modifier в Java

private
(По умолчанию)
protected
public

2- Обзор access modifier

Access Modifier	Доступ внутри класса?	Доступ внутри пакета?	Доступ снаружи пакета подклассом?	Доступ снаружи пакета не в подклассе?
private	Y
по умолчанию	Y	Y
protected	Y	Y	Y
public	Y	Y	Y	Y

3- private access modifier

Вы не можете получить доступ к полю private вне класса, который определяет его как private. Java оповестить об ошибке во время компиляции класса.

4- private constructor

Если вы создаете класс и имеете конструктор private, вы не можете создать объект этого класса из того конструктора private, вне этого класса. Посмотрим изображенный пример:

5- Access modifier по умолчанию

В случае, если вы объявляете поле, метод, или конструктор (constructor), class, .. но не пишете точно access modifier, это означает что он является access modifier по умолчанию.

Рамки доступа access modifier по умолчанию это внутри package.

 // A class with default access modifier // (Not public). class MyClass < // A field with private access modifier. private int myField; // A field with default access modifier. // (not specified public, protected, private). String myField2; // A method with default access modifier. // (not specified public, protected, private). void showMe() < >>

С интерфейсом, когда вы объявляете поле (Field) или метод (Method) вам всегда нужно объявлять public или ставить по умолчанию, но Java всегда будет понимать это как public.

 public interface MyInterface < // This is a field, you can not declare private or protected. public static int MY_FIELD1 = 100; // This is a field with default access modifier // But Java considering this is a public. static int MY_FIELD2 = 200; // This is a method, with default access modifier // But Java considering this is a public. void showInfo(); >

6- protected access modifier

protected access modifier может получить доступ внутри package, или снаружи package но только через наследственность.

protected access modifier применяется только для поля, метода и конструктора. Не может применяться для класса (class, interface, enum, annotation).

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7- public access modifier

public access modifier это самы сильный и может получить доступ везде. Он имеет самый широкий диапазон доступа по сравнению с другими modifier.

8- Метод переопределения

Вы можете переопределить метод родительского класса, метод которого имеет одинаковое название и параметр в подклассе. Но вы не можете ограничить рамки доступа этого метода.

Class Cat расширенный из class Animal и переопределить метод move(), переопределть рамки доступа из protected в public, это действительно.
Class Mouse расширенный из class Animal и переопределить метод move(), ереопределть рамки доступа из protected в по умолчанию, уменьшает рамки доступа корневого метода, это неразрешено.