CODEWITHSUNDEEP
java
Abhishek Singh
Abhishek Singh

Reputation: 9765

Keeping only semicolon in code is allowed in java. What happens behind the scene ? How compiler and JVM treats them?

public static void main(String[] args) {
    File dir = new File("dir");
    dir.mkdir();

    File file = new File(dir,"file.txt");;;;;
    ;
    ;
    ;
    try {
        file.createNewFile();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        ;
        ;
        ;
        ;
    }



}

Compiler shows no error for the extra semi-colons. And code runs as if nothing wrong happened. I want to know what happens behind scene ? Does including such semi-colon consume more of stack memory , and thus require more processor cycles to run ?

Upvotes: 1

Views: 395

Answers (2)

aioobe
aioobe

Reputation: 421100

I want to know what happens behind scene ?

An extra ; turns up as a skip statement in the AST.

They are typically used instead of empty bodies in for instance while loops:

while (expression)
    ;

Does including such semi-colon consume more of stack memory , and thus require more processor cycles to run ?

No, it does not show up in the byte code. (Which is why they typically can't be used as break statements when debugging.)

Some trivia:

You may actually have skip statements outside of classes:

class MyClass {
    // ...
}

;;;;;

These are ignored, and allowed simply to not annoy people coming from C++ and are used to put ; after a class:

class MyClass {
    // ...
};

Upvotes: 10

Aniket Thakur
Aniket Thakur

Reputation: 68975

They are removed by compiler just like comments. You can see the bytecode - 

public class Test
{
    public static void main(String args[])
    {
        System.out.println("Hi there!");
        ;
        //this is a comment
        System.out.println("Bye there!");
    }
}

and bytecode is

Compiled from "test.java"
public class Test extends java.lang.Object{
public Test();
  Code:
   0:   aload_0
   1:   invokespecial   #1; //Method java/lang/Object."<init>":()V
   4:   return

public static void main(java.lang.String[]);
  Code:
   0:   getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   3:   ldc     #3; //String Hi there!
   5:   invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

   8:   getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   11:  ldc     #5; //String Bye there!
   13:  invokevirtual   #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

   16:  return

}

As it does not every generate a byte code no extra memory is taken by it.

Upvotes: 1

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