The Initializer Block in Java


Initializer block contains the code that is always executed whenever an instance is created. It is used to declare/initialize the common part of various constructors of a class. For example,

public class GFG
    // Initializer block starts..
        // This code is executed before every constructor.
        System.out.println("Common part of constructors invoked !!");
    // Initializer block ends

    public GFG()
        System.out.println("Default Constructor invoked");
    public GFG(int x)
        System.out.println("Parametrized constructor invoked");
    public static void main(String arr[])
        GFG obj1, obj2;
        obj1 = new GFG();
        obj2 = new GFG(0);


Common part of constructors invoked!!
Default Constructor invoked
Common part of constructors invoked!!
Parametrized constructor invoked 

We can note that the contents of initializer block are executed whenever any constructor is invoked (before the constructor’s contents)

The order of initialization constructors and initializer block doesn’t matter, initializer block is always executed before constructor. See this for example.

Refer below article for more details in instance initialization:
Instance Initialization Block (IIB) in Java

What if we want to execute some code once for all objects of a class?
We use Static Block in Java

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