Java what is package protected

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.

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Различие между модификаторами доступа public, protected, package-private и private в Java

Часто, при работе с классами и интерфейсами в Java, перед разработчиками встает вопрос выбора подходящего модификатора доступа. Иногда сложно понять, в каких случаях лучше использовать public , protected , private или package-private (по умолчанию).

Для примера, представим класс, который содержит различные методы и переменные. В этом классе есть некоторые методы, которые должны быть доступны только внутри класса, некоторые доступны только в пределах одного пакета, некоторые доступны в классах-наследниках, а некоторые должны быть доступны в любом месте программы. Вот здесь и начинают играть роль модификаторы доступа.

Модификатор private делает члены класса (переменные, методы и т.д.) доступными только внутри самого этого класса. Они не будут доступны ни в пределах пакета, ни в классах-наследниках, ни где-либо ещё. Этот модификатор обычно используется для скрытия внутренней реализации класса.

Package-private (по умолчанию)

Если модификатор доступа не указан, то он считается package-private . Члены класса с таким модификатором доступа будут доступны только в пределах того же пакета. Это полезно, когда требуется разделить код на логические модули, но при этом дать доступ к некоторым составляющим модулю другим его частям.

Члены класса, помеченные модификатором protected , будут доступны в пределах того же пакета и во всех классах-наследниках, независимо от того, в каком пакете они находятся. Это обычно используется в ситуациях, когда нужно предоставить расширяемую функциональность в подклассах.

Если член класса объявлен как public , он будет доступен в любом месте программы. Этот модификатор доступа часто используется для общедоступных методов и переменных, которые должны быть доступны везде.

Таким образом, выбор модификатора доступа зависит от того, где и как планируется использовать члены класса. Нужно внимательно продумать архитектуру программы и определить, какой уровень доступа необходим для каждого элемента класса.

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What is package protected in Java?

The protected modifier specifies that the member can only be accessed within its own package (as with package-private), and furthermore by a subclass of its class in another package. The third column indicates whether subclasses of the class declared outside of this package have access to the member.

What is protected CS?

The protected keyword is a member access modifier. This page covers protected access. The protected keyword is also part of the protected internal and private protected access modifiers. A protected member is accessible within its class and by instances of derived classes.

Does the Java package provide access protection?

In java, access modifiers define the accessibility of the class and its members. For example, private members can only be accessed within members of the same class. 🔔 Private members can only be accessed within the same class. …

Which access modifier is also known as a package-level access modifier?

If a class is declared as default, we can access that class only inside the current package, that is, from the external package we cannot access it. Therefore, the default access modifier is also known as the package-level access modifier.

How do I access protected methods?

The protected keyword in Java refers to one of its access modifiers. Methods or data members declared as protected can be accessed from: Within the same class. Subclasses of the same packages.

Why is the void protected?

protected is an access modifier and means that access is limited to the containing class or types derived from the containing class. void is the return type of the method and means that it does not return anything.

How do packages provide access protection?

Access modifiers in Java specify the accessibility or scope of a field, method, constructor, or class. Protected: The access level of a protected modifier is inside the package and outside the package through the child class. If you don’t create the child class, it can’t be accessed from outside the package.

What is package in Java with example?

Package in Java is a mechanism for encapsulating a group of classes, subpackages, and interfaces. Packages are used to: Prevent name conflicts. For example, there may be two classes named Employee in two packages, college. Employee and university.

Can a class declared as private be accessed outside of its package?

Can a class declared as private be accessed outside of its package? Impossible. Protected access modifier cannot be applied to class or interfaces. Methods and fields can be declared protected, however methods and fields in an interface cannot be declared protected.

Can a class be private in Java?

Java only allows public and default modifiers for top level classes in Java. Inner classes can be private.

How do packages avoid namespace collision in Java?

Packages avoid namespace collision: a package cannot contain two classes with the same names, but two different packages can have a class with the same name. The exact name of the class is identified by its package structure. They can be divided into two categories: User-defined packages.

What makes a package a package in Java?

Packages in Java A package is a collection of similar types of Java entities, such as classes, interfaces, subclasses, exceptions, errors, and enumerations. A package can also contain sub-packages. Advantages of using Packages in Java

Where to find package version information in Java?

See Java Language Changes for a summary of updated language features in Java SE 9 and later. See the JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK versions. You may need to include package version information in the manifest of a JAR file.

What is an example of access protection in Java?

For example, private members can only be accessed within members of the same class. Java has four access modifiers, and they are default, private, protected, and public. In java, package is a container of classes, subclasses, interfaces, and subpackages.

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