K&B Ch3 Self Test Que 14: need more clarification

[Thillakan Saba]

class Bird {
{ System.out.print("bl "); }
public Bird() { System.out.print("b2 "); }
}
class Raptor extends Bird {
static { System.out.print("r1 "); }
public Raptor() { System.out.print("r2 "); }
{ System.out.print("r3 "); }
static { System.out.print("r4 "); }
}
class Hawk extends Raptor {
public static void main(String[] args) {
System.out.print("pre ");
new Hawk();
System.out.println("hawk ");
}
}

I expected :
pre r1 r4 pre bl b2 r3 r2 hawk

but output is
r1 r4 pre bl b2 r3 r2 hawk

why it does not print the first SOP?

[Akhilesh Trivedi]

Because,
1. Parent class is loaded before the child class.
2. When a class is loaded static-blocks are executed first + static variables are initialized to defaults + instance variables are set to their default values.
3. Constructor of parent class is first executed before the execution of the child class constructor.

[Thillakan Saba]

We can split these as three cases :



First case ::
class Bird {
{ System.out.print("bl "); }
public Bird() { System.out.print("b2 "); }
}
class Raptor extends Bird {
static { System.out.print("r1 "); }
public Raptor() { System.out.print("r2 "); }
{ System.out.print("r3 "); }
static { System.out.print("r4 "); }
}
class Hawk extends Raptor
{
public static void main(String[] args) {
System.out.print("pre ");
System.out.println("hawk ");
}
}

OutPut
r1 r4 pre hawk

Second Case:::

class Bird {
{
System.out.print("bl ");
}
public Bird() { System.out.print("b2 "); }
}
class Raptor extends Bird {
static {
System.out.print("r1 ");
}
public Raptor() { System.out.print("r2 "); }
{ System.out.print("r3 "); }
static { System.out.print("r4 "); }
}
class Hawk extends Raptor
{
public static void main(String[] args) {
System.out.print("pre ");
new Hawk();
System.out.println("hawk ");
}
}

output ::
r1 r4 pre bl b2 r3 r2 hawk


Third case :::

class Bird {
{
System.out.print("bl ");
}
public Bird() { System.out.print("b2 "); }
}
class Raptor extends Bird {
static {
System.out.print("r1 ");
}
public Raptor() { System.out.print("r2 "); }
{ System.out.print("r3 "); }
static { System.out.print("r4 "); }
}
class Hawk
{
public static void main(String[] args) {
System.out.print("pre ");
new Raptor ();
System.out.println("hawk ");
}
}


Output :::

pre r1 r4 bl b2 r3 r2 hawk

[Deepak Vadgama]

The static block of code is called,
when the classes are loaded,
in the same order as they appear in the source code


The code

{
System.out.print("bl "); 
}

is called, initializer block (without the static keyword)

The Java compiler copies initializer blocks into every constructor.
Thus it becomes part of constructor, called only when a Object is created,
and not when a class is loaded.


Please refer to the following link for more clarification
http://java.sun.com/docs/books/tutorial/java/javaOO/initial.html

[Burkhard Hassel]

Hi ranchers,

could you use code tags for propper indentation please? Just as Deepak did?

To indent your code properly:

At the posting page, mark the part of your posting that should be indented. Usually that will be your code (or some tabellaric output).

Hit the - Button below.
that's it!


Yours,
Bu.