java

[floodfill]

an empty .java is compilable by javac, or even class A{} in A.java is compilable.

[mathiasbynens]

Could you send a pull request for this?

[alrra]

Personally, I don't think this should be included in this project.

an empty .java is compilable by javac

That is because javac reads the file, sees that no class is declared, and finishes. Therefore, no .class files will be created, so there is nothing for the JVM to execute.

or even class A{} in A.java.

$ ls 
A.java
$ cat A.java 
class A{}
$ javac A.java 
$ ls 
A.class A.java
$ java A
Exception in thread "main" java.lang.NoSuchMethodError: main

[mukulgoel1989]

Yes, that is true and it is supposed to compile. The purpose of compiler is to compile the code and generate bytecode that can then be executed by the JVM

In the two cases you point.

An empty .java file : here in this case javac compiles the file, checks for syntax errors (which there are none) and then finishes compilation. No .class file is generated as the javac generates .class file for each class and anonymous classes. Since there is no class hence no .class file.

An A.java file with class A{} : here the javac compile the file, checks syntax errors (which are none) and generates an A.class file.

in either of the case, its not the compilers job to check if the .java file makes sense or not or it will give an runtime error or not. Compiler checks for syntax and compile time issues and generates bytecode if successful.

[wakingrufus]

As of Java 21, this is a valid program:

void main() {}

Reference: https://openjdk.org/jeps/445