How to check if a Java source file is valid (has no errors)?

Question

In my code I open my file.java and parse him with JavaParser.

FileInputStream in = new FileInputStream(".../file.java");

        CompilationUnit cu;

        try {
            // parse the file
            cu = JavaParser.parse(in);
        } finally {
            in.close();
        }

........

file.java:

public class File{

     public void ownMethod(){...}

     public static void main(String[] args){

          ownMethod(5); //Note the extra parameter

     }
}

In file.java there is an error: The method main calls the method ownMethod with one parameter, but ownMethod expects 0 parameters. JavaParser doesn't detect this error and parses file.java with this error. How can I know (in my code) whether file.java has no errors? Is it posible without using a java compiler?

No problem, its those small things you never see yourself. :) — Phiwa
– Phiwa, Commented Dec 7, 2014 at 18:25
This is possible with the Eclipse JDT eclipse.org/jdt . Of course, this is a Java Compiler in some sense, but it can be deployed as a bunch of JARs. — Marco13
– Marco13, Commented Dec 8, 2014 at 9:21

ursa · Accepted Answer · 2014-12-07 18:31:45Z

5

Is it posible without using java compiler?

No. Any solution, which your (re?)invent, will lead you to yet-another-one compiler. Parse & validate for errors is an essential part of compiler's job.

answered Dec 7, 2014 at 18:31

ursa

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3 Comments

MightyPork Over a year ago

Well IDE can verify that without explicitly compiling it (yes, it actually DOES compile it, but in background and you never see it, so that counts I guess)

lexicore Over a year ago

@MightyPork Explicitly or implicitly, it does compile it. So ursa's point stands.

Federico Tomassetti Over a year ago

I agree: there are many things for which you basically need a compiler. However we are planning to build some validation in JavaParser itself in the future, so we can check if the AST is valid. For a full validation we would also need to use JavaSymbolSolver, which resolve types and method calls. It basically re-implement a lot of stuff you find in a compiler.

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