CODEWITHSUNDEEP
java
João Pedro Schmitt
João Pedro Schmitt

Reputation: 1498

Java 11 doesn't run main method if the public class is not declared first

I created the following Chimpazee.java file with the following content:

class Primate {
    public Primate() {
        System.out.print("Primate-");
    }
}

class Ape extends Primate {
    public Ape(int fur) {
        System.out.print("Ape1-");
    }
    public Ape() {
        System.out.print("Ape2-");
    }
}

public class Chimpazee extends Ape {
    public Chimpazee() {
        super(2);
        System.out.print("Chimpazee-");
    }
    public static void main(String[] args) {
        new Chimpazee();
    }
}

However, when I try to execute this file on Windows 10 + PowerShell using Java 11...

PS C:\projects\ocp-java-se\java-se-11\chapter8> java -version
java version "11.0.11" 2021-04-20 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.11+9-LTS-194)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.11+9-LTS-194, mixed mode)

I'm getting a runtime error with the following command

PS C:\projects\ocp-java-se\java-se-11\chapter8> java .\Chimpazee.java
error: can't find main(String[]) method in class: Primate

If I move the Chimpazee class to the beginning of the file it works fine. Isn't suppose to Java compile this independent of the sequence of the classes?

Upvotes: 5

Views: 506

Answers (1)

Arvind Kumar Avinash
Arvind Kumar Avinash

Reputation: 79425

JEP 330 mentions it as:

The class to be executed is the first top-level class found in the source file. It must contain a declaration of the standard public static void main(String[]) method.

i.e. you need to make public class Chimpanzee as the top-level class as follows:

public class Chimpanzee extends Ape {
    public Chimpanzee() {
        super(2);
        System.out.print("Chimpanzee-");
    }
    public static void main(String[] args) {
        new Chimpanzee();
    }
}

class Primate {
    public Primate() {
        System.out.print("Primate-");
    }
}

class Ape extends Primate {
    public Ape(int fur) {
        System.out.print("Ape1-");
    }
    public Ape() {
        System.out.print("Ape2-");
    }
}

Then, run it as

java Chimpanzee.java

Output:

Primate-Ape1-Chimpanzee-

Upvotes: 5

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