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Editor to share with you what Java modifiers are, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

Java modifier

The Java language provides many modifiers, which are mainly divided into two categories: access modifiers and non-access modifiers

Modifiers are used to define classes, methods, or variables, usually at the front of the statement. Let's use the following example to illustrate:

Public class className {

/ /...

}

Private boolean myFlag

Static final double weeks = 9.5

Protected static final int BOXWIDTH = 42

Public static void main (String [] arguments) {

/ / method body

}

. . .

Access control modifier

In Java, access controllers can be used to protect access to classes, variables, methods, and constructors. Java supports four different access rights.

-the default, also known as default, is visible in the same package without any modifiers.

-Private, specified with the private modifier, visible within the same class.

Common, specified with the public modifier, visible to all classes.

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-protected, specified with the protected modifier, visible to classes and all subclasses in the same package.

1. Default access modifier-do not use any keywords

Variables and methods declared with the default access modifier are visible to classes in the same package. Variables in the interface are implicitly declared as public static final, while methods in the interface have access permissions of public by default.

Example:

As shown in the following example, variables and methods can be declared without any modifiers.

String version = "1.5.1"

Boolean processOrder () {

Return true

}

two。 Private access modifier-private

Private access modifiers are the strictest access level, so methods, variables, and constructors declared as private can only be accessed by the class to which they belong, and classes and interfaces cannot be declared as private.

Variables declared as private access types can only be accessed by external classes through public getter methods in the class.

The use of Private access modifiers is mainly used to hide the implementation details of the class and protect the data of the class.

The following classes use private access modifiers:

Public class Logger {

Private String format

Public String getFormat () {

Return this.format

}

Public void setFormat (String format) {

This.format = format

}

}

Instance, the format variable in the Logger class is a private variable, so other classes cannot directly get and set the value of the variable. To enable other classes to manipulate the variable, two public methods are defined: getFormat (), which returns the value of format, and setFormat (String), which sets the value of format.

3. Public access modifier-public

Classes, methods, constructors, and interfaces declared as public can be accessed by any other class.

If several public classes that access each other are distributed in different packages, you need to import the package where the corresponding public class resides. Because of the inheritance of the class, all public methods and variables of the class can be inherited by its subclasses.

The following functions use public access control:

Public static void main (String [] arguments) {

/ /...

}

The main () method of the Java program must be set to public, otherwise the Java interpreter will not be able to run the class.

4. Protected access modifier-protected

Variables, methods, and constructors declared as protected can be accessed by any other class in the same package or by subclasses in different packages.

Protected access modifiers cannot modify classes and interfaces, methods and member variables can be declared as protected, but interface member variables and member methods cannot be declared as protected.

Subclasses can access the methods and variables declared by the Protected modifier, thus protecting unrelated classes from using these methods and variables.

The following parent class uses the protected access modifier, and the child class overloads the parent class's openSpeaker () method.

Class AudioPlayer {

Protected boolean openSpeaker (Speaker sp) {

/ / implementation details

}

}

Class StreamingAudioPlayer {

Boolean openSpeaker (Speaker sp) {

/ / implementation details

}

}

If you declare the openSpeaker () method as private, classes other than AudioPlayer will not be able to access the method. If you declare openSpeaker () as public, then all classes can access the method. If we only want the method to be visible to the subclasses of its class, declare the method as protected.

. .

Access control and inheritance

Note the rules inherited by the following methods:

Methods declared as public in the parent class must also be public in the subclass.

Methods declared as protected in the parent class are either declared as protected or public in the subclass. Cannot be declared as private.

Methods declared by default modifiers in the parent class can be declared as private in the subclass.

Methods declared as private in the parent class cannot be inherited.

.

Non-access modifier

To implement some other functions, Java also provides a number of non-access modifiers.

The static modifier is used to create class methods and class variables.

Final modifiers are used to modify classes, methods, and variables. Final-modified classes cannot be inherited, modified methods cannot be redefined by inherited classes, and modified variables are constants and cannot be modified.

Abstract modifier, which is used to create abstract classes and abstract methods.

Synchronized and volatile modifiers, mainly for thread programming.

. . .

1. Static modifier

Static variable:

The static keyword is used to declare static variables independent of objects, and no matter how many objects a class instantiates, its static variables have only one copy. Static variables are also called class variables. Local variables cannot be declared as static variables.

Static method:

The static keyword is used to declare static methods independent of the object. Static methods cannot use non-static variables of a class. The static method takes the data from the parameter list and calculates the data.

Access to class variables and methods can be directly accessed using classname.variablename and classname.methodname.

2. Final modifier

Final variable:

Final variables can be explicitly initialized and can only be initialized once. References to objects declared as final cannot point to different objects. But the data in the final object can be changed. That is, the reference to the final object cannot be changed, but the value inside can be changed.

The final modifier is usually used with the static modifier to create class constants.

. .

Final method

Final methods in a class can be inherited by subclasses, but cannot be modified by subclasses.

The main purpose of declaring the final method is to prevent the contents of the method from being modified.

. .

Final class

The final class cannot be inherited, and no class can inherit any feature of the final class.

3. Abstract modifier

Abstract classes:

Abstract classes cannot be used to instantiate objects, and the only purpose of declaring an abstract class is to extend it in the future.

A class cannot be modified by both abstract and final. If a class contains abstract methods, the class must be declared as an abstract class, otherwise a compilation error will occur.

Abstract classes can contain abstract and non-abstract methods.

. .

Abstract method

An abstract method is a method without any implementation, and the concrete implementation of this method is provided by subclasses. Abstract methods cannot be declared as final and static.

Any subclass that inherits an abstract class must implement all abstract methods of the parent class, unless the subclass is also an abstract class.

If a class contains several abstract methods, the class must be declared abstract. An abstract class may not contain abstract methods.

The declaration of an abstract method ends with a semicolon, for example: public abstract sample ()

4. Synchronized modifier

Methods declared by the synchronized keyword can only be accessed by one thread at a time. The Synchronized modifier can be applied to four access modifiers.

5. Transient modifier

When the serialized object contains an instance variable decorated by transient, the java virtual machine (JVM) skips that specific variable.

This modifier is included in the statement that defines the variable and is used to preprocess the data type of the class and variable.

6. Volatile modifier

Each time a volatile-decorated member variable is accessed by a thread, it forces the value of the member variable to be reread from shared memory. Also, when a member variable changes, the thread is forced to write back the change value to shared memory. So that at any time, two different threads always see the same value of a member variable. A volatile object reference may be null.

The above is all the content of the article "what are the modifiers of Java". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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