什么是MyClass.class？ [英] what is MyClass.class?

问题描述

以下是MainClass.java中列出的代码。

following is the code listed in MainClass.java.

public class MainClass {

    public static void main(String[] args) {

        System.out.println("main started...");

        Class c = MyClass.class ;
                        //this class variable seems to be public static.
                        //But, as it is clearly visible in the MyClass,
                        //no reference variable is declared.
                        //My problem is that from where this class variable
                        //came from.
                        //i also check out the Object.java file, but it also don't
                        //have any public static class variable of Class class
                        //like there is
                        //out (instance of PrintStream class) in System class.
                        //Hope all u mindoverflow guys help me to sort out
                        //this probz.

        try {
            Class.forName( c.getName() ) ;

            System.out.println("classloader of MyClass : " + MyClass.class.getClassLoader());

            System.out.println("classloader of MyClass : " + String.class.getClassLoader());
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

        System.out.println("main ended...");
    }
}

class MyClass{
    static{
        System.out.println("static block of MyClass class.");
    }
}

thnx coobird ...
i找到了文章非常有用。 ：）

thnx coobird... i found the article quite useful. :)

但是，关于文学作品，我的知识仅限于：

But, about litereals my knowledge is only limited to:

int i = 5 ;  //here 5 is an integer literal

float f = 5.6f ;  //here 5.6f is a float literal

唯一的非原始文字，我知道是

the only non-primitive litereal, i know is

String str = "java" ;   //"java" is a String litereal

和类文字，你和Jon Skeet明确表示我非常好。

and class literal, which u and Jon Skeet make clear to me very well.

在java中找到更多的文字???

同意...
因此根据讨论，总文字归类为： -

agreed... so as per the discussion, total literals are categorized as:-

• 原始文字


• 字符串文字


• class literal


• null

• primitive literals
• string literals
• class literal
• null

还有更多的文字（为了让列表更长一点：））

are there some more literals (to make the list a little longer :) )

当我使用decomipler反编译MainClass.class时，两个Class
类型的静态变量（可能是因为，我使用过发现类文字2次）被自动添加，但从未在代码中找到使用
。此外，两个类文字都直接替换为我在java文件中使用它们的类文件。

when i decompile the MainClass.class using decomipler, two Class type static variables (may be coz, i have used class literal 2 times) are found to be automatically added, but never found to be used in the code. Also, both the class literals are directly replaced from the class file where i have used them in the java file.

My代码： -

public class MainClass {

    public static void main(String[] args) {

        System.out.println("main started...");

        Class c = MyClass.class ;

        try {
            Class.forName( c.getName() ) ;

            System.out.println("classloader of MyClass : " + MyClass.class.getClassLoader());

            System.out.println("classloader of MyClass : " + String.class.getClassLoader());
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

        System.out.println("main ended...");
    }
}

反编译生成的代码： -

import java.io.PrintStream;

public class MainClass
{

    public MainClass()
    {
    }

    public static void main(String args[])
    {
        System.out.println("main started...");
        Class c = MyClass;
        try
        {
            Class.forName(c.getName());
            System.out.println((new StringBuilder("classloader of MyClass : ")).append(MyClass.getClassLoader()).toString());
            System.out.println((new StringBuilder("classloader of MyClass : ")).append(java/lang/String.getClassLoader()).toString());
        }
        catch(ClassNotFoundException e)
        {
            e.printStackTrace();
        }
        System.out.println("main ended...");
    }

    static Class class$0;
    static Class class$1;
}

推荐答案

这是类文字 - 获取特定类型的类< T> 的简单方法。

It's "class literal" - a simple way of getting the Class<T> for a particular type.

参见 Java语言规范的第15.8.2节以获取更多详细信息。

See section 15.8.2 of the Java Language Specification for more details.

请注意，它不是该类的字段，它是一种特殊的语法糖。

Note that it's not a "field" of the class, it's a special piece of syntactic sugar.

由于类型擦除，您可能会遇到有关泛型的有趣限制。 TypeLiteral < Guice中引入的/ code> 提供了更多信息和解决方法。

Due to type erasure, you may run into interesting restrictions around generics. The TypeLiteral introduced in Guice gives more information and a workaround.

在实现方面，它取决于您要定位的字节码版本。如果您使用 -target 1.4 （或以下），则会在代码中插入对 Class.forName（）的调用在类型初始化期间调用的静态方法中。如果使用 -target 1.5 （或以上），常量池将获得类条目。我不知道如何处理这个细节。

In terms of implementation, it depends on which bytecode version you're targeting. If you use -target 1.4 (or below), a call to Class.forName() is inserted into your code in a static method which is called during type initialization. If you use -target 1.5 (or above) the constant pool gets a "class" entry. I don't know the details of how this is handled though.

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