如果编译一个空的Java文件会怎样？

Question

When I compiled an empty Java file it didn't produce any class file. So I want to know how compiler react when compiling an empty Java file? I thought it should generate an empty class file in this case, but it did not. So why it didn't?

Answer 1

javac starts, sees there is no class declared in the file, and finishes. In order for a .class file to be created you must at least have the class declaration in the file.

Answer 2

What most of the answers are saying is really that a class file is not a compiled java file but a binary representation of a class.

Compiling a java file could result in two class files if the java file contains two classes (although only one can be public) and that is why compiling something with zero classes will result in zero class files.

Answer 3

Well given that a Java file could be like this:

// Foo.java 
class Bar
{
}

How would it know what to call the thing? Also should it make it a class or an interface or an enum?

Rather than make the choice for you it does nothing (I would have expected an error myself... but nothing is a sane thing to do as well).

Answer 4

If the file is totally empty and just called .java then there is nothing for the compiler to do when you attempt to generate a class file. If you do have a

class Foo {
}

segment in the .java file then an empty calss file (Foo.class) will be generated

Answer 5

javac creates a class file for each class declaration (explicit or anonymous). since your java file contained none, the compiler justly didn't generate any class files.

Answer 6

If you would've declared the class, (eg, public class test{ } ), it would compile and create test.class file. It would not run b'cos it doesn't have a main method.

Answer 7

class Emptyclass { }

//Emptyclass can be compiled sucessfully and .class file is also generated, but during execution it fails, because JVM doesnot find 'Main Method' in class 'Emptyclass'

Answer 8

Java will not create class file of that java file. Because First it will look for class name. So nothing will happen

Answer 9

Javac启动并检查文件的大小，如果大小为零，则它仅返回而未创建任何.class文件。