i am not getting any error while not using main method in java 18 version

Question

i am using Static block without using main method in java version "18.0.2" 2022-07-19 the code is perfectly working without any compile error and runtime error how is this possible?

class StaticBlockPrint{

    static {

        System.out.println("Hello world!");
        int i = 8;
        i =i+8;
 
        System.out.println(i);
        System.exit(0);
    }
}

`main` is not required for compilation. it is required for execution. Try an *run* your class. — Federico klez Culloca, Aug 27 '22 at 08:19
Are you sure you are using version 18? This behaviour was legal prior to Java 7. Check your compile level, make sure it is 18 and run it again on the same version. — deHaar, Aug 27 '22 at 08:24
yes i am using java 18 E:\Software Testing\Java Program>java -version java version "18.0.2" 2022-07-19 Java(TM) SE Runtime Environment (build 18.0.2+9-61) Java HotSpot(TM) 64-Bit Server VM (build 18.0.2+9-61, mixed mode, sharing) — Mahipal bisht, Aug 27 '22 at 08:33
There's nothing mysterious to here. If the class is loaded, the static block is executed. This class must be referenced either directly or indirectly from the main class being run. — Bohemian, Aug 27 '22 at 09:13
@Bohemian Not "mysterious" but let's say "special" - that it can be run as an *application* — g00se, Aug 27 '22 at 09:21

score 4 · Answer 1 · answered Aug 27 '22 at 11:41

I can only reproduce the behavior when using java StaticBlockPrint.java but then, in all versions since JDK-11.

When I compile with javac and run with java StaticBlockPrint, all versions since Java 7, including 18.0.2.1, consistently produce an error regarding the missing main method.

Technically, the difference is tiny. The class initializer ends with System.exit(0);, so when it is executed before the missing main method is about to be reported, the process is terminated without an error message.

The following program demonstrates two variants of how a launcher could be implemented

class Initializer {
    public static void main(String... arg) {
        ClassLoader cl = Initializer.class.getClassLoader();

        // variant 1
        try {
            cl.loadClass("A").getMethod("main");
        }
        catch(Throwable t) {
            System.out.println("A: " + t);
        }

        // variant 2
        try {
            Class.forName("B", true, cl).getMethod("main");
        }
        catch(Throwable t) {
            System.out.println("B: " + t);
        }
    }
}
class A {
    static {
        System.out.println("A initialized");
    }
}
class B {
    static {
        System.out.println("B initialized");
    }
}

A: java.lang.NoSuchMethodException: A.main()
B initialized
B: java.lang.NoSuchMethodException: B.main()

i am not getting any error while not using main method in java 18 version

1 Answers1