文件名和类名在java中不同 [英] File name and class name different in java

问题描述

我创建了一个名为In.java的文件，输入以下代码：

  class In {
 int a; 
 
 public static void main（
 String args []）{
继承h = new Inheritance（）; $ b $ h h.set（6）; 
 System.out.println（h.get（））; 
} 
 
 void set（
 int a）{
 this.a = a; 
} 
 
 int get（）{
 System.out.println（a）; 
 return a; 
} 
} 
  

当我编译它时显示了一个关于继承的错误。然后我重命名为In as I Inheritance

  class Inheritance {
 int a; 
 
 public static void main（
 String args []）{
继承h = new Inheritance（）; 
 h.set（6）; 
 System.out.println（h.get（））; 
} 
 
 void set（
 int a）{
 this.a = a; 
} 
 
 int get（）{
 System.out.println（a）; 
 return a; 
} 
} 
  

现在当我编译它编译并创建Inheritance.class但文件名是In.java，当我编译为 public class Inheritance 它提醒我该类应该更改为Inheritance.java。现在当我运行 java在它显示一个错误为错误：无法找到或加载主类在将类重命名为In as

  class In {
 int a; 
 
 public static void main（
 String args []）{
继承h = new Inheritance（）; 
 h.set（6）; 
 System.out.println（h.get（））; 
} 
 
 void set（
 int a）{
 this.a = a; 
} 
 
 int get（）{
 System.out.println（a）; 
 return a; 
} 
} 
  

现在当我编译时编译为In.class当我运行输出它运行程序显示

6
6

该程序与In.java并运行类的名称为类继承它编译并给出了Inheritance.class。
1.如果类名和文件名不同，编译器会出现错误吗？
当我运行 java In 它显示错误：无法找到或加载主类在因为生成了In.class文件为什么在编译In.java时没有检测到类名为Inheritance的类？所以一个类文件可以在同一目录中使用任何其他类文件？

解决方案

> public 应保存在同名的文件中。如果公用类的名称和包含它的文件不同，那么这是一个编译错误。未声明为 public 的类可以保存在不同名称的文件中。

请注意，生成的类文件是以java类命名的，而不是文件名。下面的例子中， X 是任何有效的名称（除外） Foo 和 Bar ）。

示例1：

  // filename X.java（不编译）
 public class Foo {
 
} 
 public class Bar {
 
} 
  

编译器抱怨公共类 Foo 和 Bar 不在自己的 .java 文件中。 / p>

示例2：

  // filename Foo.java t compile）
 public class Foo {
 
} 
 public class Bar {
 
} 
  pre> 
 
 
错误与上述相同，但此次只适用于 Bar 。
 
 
 
示例3：
  // filename Foo.java（compiles）
 public class Foo { 
 
} 
 class Bar {
 
} 
  
 
 $ b b 
生成的文件是 Foo.class 和 Bar.class 。
 
 
 
示例4：
  // filename X.java（compiles）
 class Foo {
 
} 
 class Bar {
 
} 
  
生成的文件是 Foo.class 和 Bar.class 。
 
I created a file named In.java an entered the following code
class In {
   int a;

   public static void main(
      String args[] ) {
      Inheritance h = new Inheritance();
      h.set( 6 );
      System.out.println( h.get() );
   }

   void set(
      int a ) {
      this.a = a;
   }

   int get() {
      System.out.println( a );
      return a;
   }
}
When I compiled it showed me an error regarding Inheritance. Then I renamed In as I Inheritance
class Inheritance {
   int a;

   public static void main(
      String args[] ) {
      Inheritance h = new Inheritance();
      h.set( 6 );
      System.out.println( h.get() );
   }

   void set(
      int a ) {
      this.a = a;
   }

   int get() {
      System.out.println( a );
      return a;
   }
}
Now when I compiled it compiled and created Inheritance.class but the file name was In.java still when I compile as public class Inheritance it alerts me that the class should be changed as Inheritance.java . now when I run java Init shows an error as Error: Could not find or load main class In Now I again renamed the class as In as
class In {
   int a;

   public static void main(
      String args[] ) {
      Inheritance h = new Inheritance();
      h.set( 6 );
      System.out.println( h.get() );
   }

   void set(
      int a ) {
      this.a = a;
   }

   int get() {
      System.out.println( a );
      return a;
   }
}
Now when I compiled it compiled as In.class and when I run the output it had run the program showing

6
6

When I created the program with In.java and run the class with name as Class Inheritance it compiled and gave the Inheritance.class . 
1. If the class name and file name are different won't the compiler show up an error?
2. when I run the java In it shows Error: Could not find or load main class In as the In.class file is generated Why doesn't it detect it while compiling In.java with class name as Inheritance ? so can one class file use any other class file in the same directory?
解决方案
Any class which is declared public should be kept in a file of the same name. It is a compilation error if the names of the public class and the file which contains it are different. A class which isn't declared public can be kept in a file of a different name. 

Note that the generated class files are named after the java classes, not the file names. Look at below examples.

In the below illustrations X is any valid name (except Foo and Bar).

Example 1:
// filename X.java (doesn't compile)
public class Foo {

}
public class Bar {

}
compiler complains about public classes Foo and Bar not being present in their own .java files.

Example 2:
// filename Foo.java (doesn't compile)
public class Foo {

}
public class Bar {

}
error same as above but applies only to Bar this time.

Example 3:
// filename Foo.java (compiles)
public class Foo {

}
class Bar {

}
generated files are Foo.class and Bar.class.

Example 4:
// filename X.java (compiles)
class Foo {

}
class Bar {

}
generated files are Foo.class and Bar.class.

                        
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