Instance initializer blocks in Java

Came across this for the first time today!  Java has instance initializer blocks for initializing instance variables, similar to static inilializer blocks for static varaibles.

Order of execution of instance initializer blocks is interesting:
  • First, any parent class constructor (called by a super method invocation in the constuctor, or the default parent class constructor) gets called.
  • Then, the instance initializer block gets called.
  • And after that, the remaining part of the constructor, after the super method call (if any) gets executed.


class Animal{  
        System.out.println("Animal constructor called");
class Cat extends Animal {
    double whiskerLength;

    Cat() {
        System.out.println("Cat constructor is executing");
    // instance initializer block
        whiskerLength = 4;
        System.out.println("instance initializer block is executing");
    public static void main(String args[]){  
        Cat cat = new Cat();

The above will output:

Animal constructor called
instance initializer block is executing
Cat constructor is executing

See also: