Order of Execution with inheritance hierarchy

[Thomas Hauck]

Question:
Why does the constructor in the parent class get executed before the "initializer statement" in the subclass?

I read that the order of execution is as follows:

1) First, static statements/blocks are called IN THE ORDER they are defined.
2) Next, instance initializer statements or blocks are called IN THE ORDER they are defined.
3) Finally, the constructor is called.

For 2) above, the 'initializer statement' in the subclass Teacher is.

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

class Person {
	Person() {
		System.out.print("CP ");
	}

	static {System.out.print("SP ");}
}

class Teacher extends Person {
	Teacher() {
		System.out.print("CT ");
	}
	{
		System.out.print("IT ");
	}
}

class Pro {
	public static void main(String[] args) {
		Person p1 = new Teacher();
	}
}
/* Program output 
SP CP IT CT 
*/

Question: Does rule number 2 above apply only for an individual class and not for a hierarchy of classes?

I would have thought that the output for the program would be

SP IT CP CT

but the program produces the output

SP CP IT CT

Please confirm.

[Jeanne Boyarsky]

Thomas Hauck wrote:
Why does the constructor in the parent class get executed before the "initializer statement" in the subclass?

... Does rule number 2 above apply only for an individual class and not for a hierarchy of classes?

Correct. The superclass has to be fully instantiated before the subclass starts. That's why the superclass initialization gets printed out first. The rules you are cited are for within the same class.

[Thomas Hauck]

For a static block in the subclass it will be executed immediately after the
static block in the parent class because it has nothing to do with inheritance.

package com.java.inheritance4;

class Person {
	Person() {
		System.out.print("CP ");
	}

	static {System.out.print("SP ");}
}

class Teacher extends Person {
	Teacher() {
		System.out.print("CT ");
	}
	static {System.out.print("AB ");} //added
	{
		System.out.print("IT ");
	}
}

class Pro {
	public static void main(String[] args) {
		Person p1 = new Teacher();
	}
}
/* Program output 
SP AB CP IT CT 
*/

Is this correct?

[E Armitage]

Static blocks are executed when the classes are accessed before objects of those classes are created.

[Thomas Hauck]

I understand that, and the program verifies that all static blocks

in the
a) parent class and
b) subclass
are executed before returning to the parent class.

The order of execution is:
1. static block in parent class
2. static block in subclass
3. Constructor in parent class
4. Initializer block in subclass
5. Constructor in Subclass

class Person {
	Person() {
		System.out.print("CP "); //3. Constructor parent class
	}

	static {System.out.print("SP ");} // 1. static block parent class 
}

class Teacher extends Person {
	Teacher() {
		System.out.print("CT "); //5. Constructor in Subclass
	}
	static {System.out.print("AB ");} //2. static block in subclass
	{
		System.out.print("IT ");// 4. Initializer block in subclass 
	}
}

class Pro {
	public static void main(String[] args) {
		Person p1 = new Teacher();
	}
}
/* Program output 
SP AB CP IT CT 
*/

[Roel De Nijs]

Thomas Hauck wrote:The order of execution is:
1. static block in parent class
2. static block in subclass
3. Constructor in parent class
4. Initializer block in subclass
5. Constructor in Subclass

Maybe add different (static) initializer blocks into parent and subclass. And also add 1 (or more) initializer block(s) in the parent class. Then you'll have a complete overview of the order of execution (even with multiple initializer blocks per class).