Initializer Block in Java

If you want to initialize an instance variable you will put that code in a constructor. In this post we'll see one alternative to using a constructor that can be used to initialize instance variables which is called initializer block in Java.

Initializer blocks for instance variables look just like static initializer blocks, but without the static keyword.

General form of Initializer block in Java

{
  // whatever code is needed for initialization 
  // goes here
}

Usage of Initializer block in Java

The Java compiler copies initializer blocks into every constructor. Therefore, this approach can be used to share a block of code between multiple constructors. If you have some common code that you want to be executed regardless of which constructor is used, that code can be put in an initializer block in Java.

Initializer block Java Example

public class InitBlockDemo {
 // no-arg constructor
 InitBlockDemo(){
  System.out.println("no-arg constructor invoked");
 }
 // constructor with one param
 InitBlockDemo(int i){
  System.out.println("constructor with one param invoked");
 }
 // initializer block
 {
  System.out.println("This will be invoked for all constructors");
 }
 public static void main(String[] args) {
  InitBlockDemo ibDemo = new InitBlockDemo();
  InitBlockDemo ibDemo1 = new InitBlockDemo(10);

 }
}

Output

This will be invoked for all constructors
no-arg constructor invoked
This will be invoked for all constructors
constructor with one param invoked

Here it can be seen that the code with in the initializer block is copied in every constructor and that code is executed when the constructor of the class is called.

That's all for this topic Initializer Block in Java. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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Related Topics

1. static Block in Java
2. Constructor Chaining in Java
3. Constructor Overloading in Java
4. Encapsulation in Java
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