java中访问修饰符

Java非访问修饰符 (Java non access modifiers)

We have 7 non-access modifiers in Java. The name of these non-access modifiers are given below,

Java中有7个非访问修饰符 。 这些非访问修饰符的名称如下所示：

1. native

   本机

2. synchronized

   已同步

3. transient

   短暂的

4. volatile

   易挥发的

5. final

   最后

6. abstract

   抽象

7. static

   静态的

We will learn all the non access modifiers one by one...

我们将一一学习所有非访问修饰符...

1)本地的 (1) native)

• "native" is a keyword which is introduced in java.

  “ native”是在Java中引入的关键字。

• "native" is the modifier applicable for methods only but it is not applicable for variable and classes.

  “本机”是仅适用于方法的修饰符，但不适用于变量和类。

• The native methods are implemented in some other language like C, C++, etc.

  本机方法以其他一些语言(如C，C ++等)实现。

• The purpose of the native method is to improve the performance of the system.

  本机方法的目的是提高系统性能。

• We know that the implementation of native methods is available in other languages so we don't need to care about the implementation.

  我们知道本机方法的实现在其他语言中也可用，因此我们不需要关心实现。

Example: We will see the way of writing native methods

示例：我们将看到编写本机方法的方式

class Native {static {// Load Native Library
System.loadLibrary("native library");
}
// Native Method Declaration
public native void display();
}
class Main {public static void main(String[] args) {Native native = new Native();
native.display();
}
}

2)同步 (2) synchronized)

• "synchronized" is the keyword applicable for methods and block.

  “已同步”是适用于方法和块的关键字。

• "synchronized" keyword is not applicable for classes and variables.

  “ synchronized”关键字不适用于类和变量。

• "synchronized" keyword is useful for multithreading if we declare a method as synchronized then at a time only one thread is allowed to operate on an object.

  如果我们将一个方法声明为“ synchronized”，那么“ synchronized”关键字对于多线程很有用，那么一次只能在一个对象上运行一个线程。

Example:

例：

class SynchronizedDisplay {public synchronized void display(String msg) {for (int i = 0; i < 2; ++i) {System.out.println(msg);
try {Thread.sleep(500);
} catch (Exception ex) {System.out.println(ex.getMessage());
}
}
}
}
class MyThread extends Thread {SynchronizedDisplay sd;
MyThread(SynchronizedDisplay sd) {this.sd = sd;
}
public void run() {sd.display("hi");
}
}
class SynchronizedClass {public static void main(String[] args) {SynchronizedDisplay sd1 = new SynchronizedDisplay();
MyThread mt1 = new MyThread(sd1);
mt1.start();
MyThread mt2 = new MyThread(sd1);
mt2.start();
}
}

Output

输出量

E:\Programs>javac SynchronizedClass.java
E:\Programs>java SynchronizedClass
hi
hi
hi
hi

3)瞬态 (3) transient)

• "transient" is a keyword introduced in java.

  “ transient”是Java中引入的关键字。

• "transient" is the modifier applicable only for variables.

  “瞬态”是仅适用于变量的修饰符。

• "transient" is the modifier not applicable for classes and methods.

  “瞬态”是不适用于类和方法的修饰符。

• "transient" is useful for serialization because at the time of serialization if we don't want to save the value of the variable to meet some security constraints.

  “瞬态”对于序列化很有用，因为在序列化时，如果我们不想保存变量的值以满足某些安全性约束。

Example:

例：

Let suppose we have a class named Transient in that class we have two-three data member fname (first name), lname (last name) and address, so the address member declared as transient so its values will not be serialized (i.e. in case of deserialization of an object we will get the default value of address variable and its defined value will be erased).

假设我们有一个名为Transient的类，在该类中，我们有2-3个数据成员fname (名字)， lname (姓氏)和address ，因此地址成员声明为transient，因此其值将不被序列化(例如，对对象进行反序列化后，我们将获取地址变量的默认值，并将其定义的值删除)。

import java.io.*;
class Serialization implements Serializable {public String fname, lname;
transient String address;
public Serialization(String fname, String lname, String address) {this.fname = fname;
this.lname = lname;
this.address = address;
}
}
public class Deserialization {public static void main(String[] args) {Serialization serialize = new Serialization("Ronit", "Jain", "Mayur vihar 1");
try {FileOutputStream fos = new FileOutputStream("E:\\Programs\\myjava.txt");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(serialize);
oos.close();
fos.close();
} catch (IOException ex) {System.out.println(ex.getMessage());
}
serialize = null;
try {FileInputStream fis = new FileInputStream("E:\\Programs\\myjava.txt");
ObjectInputStream ois = new ObjectInputStream(fis);
serialize = (Serialization) ois.readObject();
ois.close();
fis.close();
System.out.println("His full name and address is :" + serialize.fname + " " + serialize.lname + " " + serialize.address);
} catch (IOException ex) {System.out.println(ex.getMessage());
} catch (ClassNotFoundException ex) {System.out.println(ex.getMessage());
}
}
}

Output

输出量

E:\Programs>javac Deserialization.java
E:\Programs>java Deserialization
His full name and address is :Ronit Jain null

4)易挥发 (4) volatile)

• "volatile" is a keyword which is introduced in java.

  “ volatile”是在Java中引入的关键字。

• "volatile" is the modifier applicable only for variables but not for methods and classes.

  “ volatile”是仅适用于变量的修饰符，不适用于方法和类。

• If the value of variable keep on changing such type of variable we have to declare with the volatile modifier.

  如果变量的值继续更改此类变量，则必须使用volatile修饰符进行声明。

• Any intermediate operation will be performed in local copy instead of the final copy.

  任何中间操作都将在本地副本而不是最终副本中执行。

Example:

例：

class VolatileVariable {// volatile keyword here makes sure that
// the changes made in one class are
// immediately reflect in other class
static volatile int volatile_var = 10;
}
class Main {public static void main(String[] args) {System.out.println("The previous value of volatile variable in one class is " + VolatileVariable.volatile_var);
VolatileVariable.volatile_var++;
System.out.println("The value changes made to the volatile variable in other class is" + VolatileVariable.volatile_var);
}
}

Output

输出量

E:\Programs>javac Main.java
E:\Programs>java Main
The previous value of volatile variable in one class is 10
The value changes made to the volatile variable in other class is 11

5)最终 (5) final)

• "final" is a keyword which is introduced in java.

  “ final”是在Java中引入的关键字。

• "final" is the modifier applicable for methods, classes, and variables.

  “最终”是适用于方法，类和变量的修饰符。

• We cannot override in child class.

  我们不能在子类中重写。

Example: Declare class as "final" and variable as final and method as final

示例：将类声明为“ final”，将变量声明为final，将方法声明为final

final class Final {final String str = "we are accessible final variable";
final void printMethod() {System.out.println("we are in final method");
}
public static void main(String[] args) {Final f = new Final();
System.out.println("final variable :" + f.str);
f.printMethod();
}
}

Output

输出量

E:\Programs>javac Final.java
E:\Programs>java Final
final variable :we are accessible final variable
we are in final method.

6)摘要 (6) abstract)

• "abstract" is a keyword which is introduced in java.

  “抽象”是在Java中引入的关键字。

• "abstract" is the modifier applicable for classes and methods.

  “抽象”是适用于类和方法的修饰语。

• If a class is abstract then we need to implement all methods of abstract class in our class.

  如果一个类是抽象的，那么我们需要在我们的类中实现所有抽象类的方法。

Example:

例：

abstract class AbstractClass {abstract void printMethod();
}
public class AbstractImplementation {public static void main(String[] args) {AbstractClass ac = new AbstractClass() {void printMethod() {System.out.println("Hi, We are in abstract class");
}
};
ac.printMethod();
}
}

Output

输出量

E:\Programs>javac AbstractImplementation.java
E:\Programs>java AbstractImplementation
Hi, We are in abstract class

7)静态 (7) static)

• "static" is a keyword introduced in java.

  “ static”是Java中引入的关键字。

• "static" member create one copy of the whole program and share it with other objects of the same program.

  “静态”成员创建整个程序的一个副本，并与同一程序的其他对象共享。

• "static" can access only static methods.

  “静态”只能访问静态方法。

Example:

例：

class StaticClass {public static int div(int a, int b) {return a / b;
}
}
class Main {public static void main(String[] args) {int p = 20, q = 10;
int div = StaticClass.div(p, q);
System.out.println("The div of p , q is" + div);
}
}

Output

输出量

E:\Programs>javac Main.java
E:\Programs>java Main
The div of p , q is2

翻译自: https://www.includehelp.com/java/what-are-the-non-access-modifiers-in-java.aspx

java中访问修饰符