code called before constructor

[varun mathur]

public class TestStaticBlock {
{
System.out.println("Varun");
}
public static void main(String[] args) {
new TestStaticBlock();
}
public TestStaticBlock() {
System.out.println("Sumit");
}

}


The output is:
Varun
Sumit

Can anyone please explain this program

[Ram Narayan.M]

public class TestStaticBlock { 
{ 
System.out.println("Varun"); 
} 
public static void main(String[] args) { 
new TestStaticBlock(); 
} 
public TestStaticBlock() { 
System.out.println("Sumit"); 
} 

} 

Varun string printing block is called "Initialization Block" which is executed during each instance creation...

What happens is... in each constructor, super() method is first method call to be executed... After finishing this constructor execution, secondly, Initialization block will be executed...

So that only, after super() call, init block is executed first, so prints "Varun" and then followed by the other instructions in the constructor...

[Abimaran Kugathasan]

UseCodeTags when you post code snaps! Have look on here

[varun mathur]

Thanks Ram
One more query . Is this initialization block is also known as static block.
If not then is there a thing such as static block?

[Abimaran Kugathasan]

There are instance initialization block and static initialization blocks! There are used for different uses! Try to find the usage with the meanings!

[varun mathur]

Abhiraman actually i got a bit confused in naming.
I read your post of "java free blocks" and now I completely understand how this code works.
thanks

[Abimaran Kugathasan]

varun mathur wrote: Abhiraman actually ....

BTW, Who is this?

[Campbell Ritchie]

What's a Java free block? I've never heard of it. What was shown in that thread was a static initialiser.

[varun mathur]

Extremely sorry for wrongly spelling out your name Abhimaran.
i was just referring to post topic when i wrote "java free block".

[Campbell Ritchie]

As I said, it's not a free block, but an initialiser. Note there are two kinds of initialiser: static and instance. You can read about them in the Java™ Language Specification §8.3.2.1 and §8.3.2.2 and §8.6 and §8.7. It isn't easy to read, however.

[Abimaran Kugathasan]

Campbell Ritchie wrote:What's a Java free block? I've never heard of it.

Are there any thing like Java free floating blocks?

[Jelle Klap]

The closest thing to a "free-floating block" - purely syntactially - is an init-block, as included in the starting post of this thread.
It seems to be unrelated to any constructor or method, but it only seems that way. This becomes very clear when you dissasemble the byte code of a class file.
You'll find that the body of an init block is copied into every constructor, default or otherwise, immidiately after the call to super(), and before the rest of the constructor body. *

For example:

package nl.jekl.javaranch;

public class Foo {
    
  { System.out.println("I'll end up a part of both constructors!"); }
  
  private String someString = "Me too!";
  
  
  public Foo() {
    System.out.println("I'm part of the explicit no-arg constructor!");
  }
  
  
  public Foo(String arg) {
    System.out.println(arg);
  }  
}

public class nl.jekl.javaranch.Foo extends java.lang.Object{
public nl.jekl.javaranch.Foo();
  Code:
   0:	aload_0
   1:	invokespecial    #10; //Method java/lang/Object."<init>":()V
   4:	getstatic	     #12; //Field java/lang/System.out:Ljava/io/PrintStream;
   7:	ldc	             #18; //String I'll end up a part of both constructors!
   9:	invokevirtual	 #20; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   12:	aload_0
   13:	ldc	             #26; //String Me too!
   15:	putfield	     #28; //Field someString:Ljava/lang/String;
   18:	getstatic	     #12; //Field java/lang/System.out:Ljava/io/PrintStream;
   21:	ldc	             #30; //String I'm part of the explicit no-arg constructor!
   23:	invokevirtual    #20; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   26:	return

public nl.jekl.javaranch.Foo(java.lang.String);
  Code:
   0:	aload_0
   1:	invokespecial    #10; //Method java/lang/Object."<init>":()V
   4:	getstatic	     #12; //Field java/lang/System.out:Ljava/io/PrintStream;
   7:	ldc	             #18; //String I'll end up a part of both constructors!
   9:	invokevirtual	 #20; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   12:	aload_0
   13:	ldc	             #26; //String Me too!
   15:	putfield	     #28; //Field someString:Ljava/lang/String;
   18:	getstatic	     #12; //Field java/lang/System.out:Ljava/io/PrintStream;
   21:	aload_1
   22:	invokevirtual    #20; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   25:	return

}

* Had the parameterized constructor included a call to this(), then the body of the init block and the initialization of someString would not have been copied (needlessly) into it.

[Campbell Ritchie]

Abimaran Kugathasan wrote: . . . Are there any thing like Java free floating blocks?

Look in the Java Language Specification. I couldn't find it there, and have never heard of it before.

[Campbell Ritchie]

Jelle Klap wrote:The closest thing to a "free-floating block" . . . is an init-block . . .

As I said earlier, what was shown previously were initialiser blocks.