a simple quetion,help

[andy lau]

when will a block without static(like this:
{//code})be execute???

[Corey McGlone]

Code within {} is known as an instance initializer and will be executed when an instance of that class is initialized. You can look in the JLS, §8.6 Instance Initializers for details.
Corey

[Ase Lindskog]

It will execute each time you construct by new Xxx() and execute before the constructor.

[andy lau]

can you explain this ? thank you very much!

  
  /*class A {
   public A() {
      System.out.println("AAA");
   }
    {System.out.println("456");}
}
public class B extends A {
   B() {
      this(12);
      System.out.println("BBB");
   }
   B(int x) {
      System.out.println("CCC");
   }
   {System.out.println("123");}
   public static void main(String[] args) {
      new B();
   }
}

/*
456
AAA
123
CCC
BBB
*/
/*

class A {
   public A() {
      System.out.println("AAA");
   }
   static {System.out.println("456");}
}
public class B extends A {
   B() {
      this(12);
      System.out.println("BBB");
   }
   B(int x) {
      System.out.println("CCC");
   }
   static {System.out.println("123");}
   public static void main(String[] args) {
      new B();
   }
}

/*456
123
AAA
CCC
BBB
*/
/*

class A {
   public A() {
      System.out.println("AAA");
   }
    {System.out.println("456");}
}
public class B extends A {
   B() {
      this(12);
      System.out.println("BBB");
   }
   B(int x) {
      System.out.println("CCC");
   }
   static {System.out.println("123");}
   public static void main(String[] args) {
      new B();
   }
}

/*123
456
AAA
CCC
BBB
*/

class A {
   public A() {
      System.out.println("AAA");
   }
   static{System.out.println("456");}
}
public class B extends A {
   B() {
      this(12);
      System.out.println("BBB");
   }
   B(int x) {
      System.out.println("CCC");
   }
    {System.out.println("123");}
   public static void main(String[] args) {
      new B();
   }
}

/*456
AAA
123
CCC
BBB*/

[ April 17, 2002: Message edited by: Cindy Glass ]

[Brian Lugo]

I will attempt to explain the first one ...
The rest you can figure out ...

class BasInvTst1 { 
public BasInvTst1() {
System.out.println("AAA");
} 
{
System.out.println("456");
}
}
public class DerInvTst1 extends BasInvTst1 {
DerInvTst1() {
this(12); 
System.out.println("BBB");
}  
DerInvTst1(int x) {
System.out.println("CCC");
}   
{
System.out.println("123");
}   
public static void main(String[] args) { 
new DerInvTst1(); 
}
}

I changed the class names.
The output is:
456
AAA
123
CCC
BBB
Here is what happens:
1. DerInvTst1 constructor with no args is called.
2. This constructor calls DerInvTst1 constructor that takes an int. arg.
3. Since there is no "this()" call on the first line, the super class's default constructor is called and super class is initialized.
4. This results in printing 456.
5. Next AAA is printed from BasInvTst1 constructor.
6. Now the derived class initialization occurs
and "123" is printed.
7. The control is then transfered to the constructor, which prints "CCC"
8. In the end the control is transfered back to DerInvTst1's no-arg constructor and "BBB" is printed.
Hope this helps,
Brian

[andy lau]

it seems that the initialiaze block is not executed before the constructor??? (because the 123 is not the first line of output)
can you tell me the exactly time when the initialize block will be executed???
[ April 17, 2002: Message edited by: andy lau ]