How can Eclipse create a class with unresolved compilation problems?

Issue

When I try to compile this class with javac, I get a compilation error and Test.class is not created.

public class Test {
    public static void main(String[] args) {
        int x = 1L;  // <- this cannot compile
    }
}

But when I create this class in Eclipse, I can see that Test.class appears in target/classes. When I try to run this class from command line with java.exe, I get

Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Type mismatch: cannot convert from long to int

Does Eclipse use its own special Java compiler to create a broken .class? How does java.exe know about complilation problems in .class?

Solution

If you decompile your class file, you can see the below main() method. That is how the Java compiler knows about the compilation error in the class.

public static void main(String[] paramArrayOfString)
{
    throw new Error("Unresolved compilation problem: \n\tType mismatch: cannot convert from long to int.\n");
}

And all this happens because the compiler (Eclipse Compiler for Java), which Eclipse uses by default/comes bundled with, is not the same as the standard Java compiler!

Answered By - Rahul