In a Java program, operations can be performed on methods, constructors, and initialization blocks. Instance Initialization Blocks or IIB are used to initialize instance variables. We know that the instance block is the name-less method in java inside which we can define logic and they possess certain characteristics. Instance block logic is common for all the objects and it will be executed only once for each object during its creation. Now, let us see the normal execution of instance blocks by creating objects.
Demonstration 1: Normal execution of instance block
Java
// Executing instance block// by creating object. // Class 1// Helper classclass GFG { { // Creation of an instance block System.out.println("Instance block called by creating objects"); }} // Class 2// Main classclass GFGJava { // main driver method public static void main(String[] args) { // Object of 1st kind GFG obj1 = new GFG(); // Object of 2nd kind GFG obj2 = new GFG(); // Object of 3rd kind GFG obj3 = new GFG(); }} |
Output:
Instance block called by creating objects Instance block called by creating objects Instance block called by creating objects
Explanation: Instance block gets executed only once for each object creation. Here it got executed for obj1, obj2, and obj3.
Demonstration 2: Executing instance block without creating an object
In Demonstration 1 we saw the execution of instance block by creating objects which are obvious but there is a misconception that an instance block can not be executed without creating an object which is not true. In our next demonstration, we will see that how can we execute an instance block without creating an object.
Java
// Executing instance// block by creating object. // Class 1// Helper classclass GFG { { // Creation of an instance block System.out.println( "Instance block called by creating objects"); }} // Class 2// Main classclass GFGJava { // main driver method public static void main(String[] args) { // Declaring instance block inside main method { System.out.println( "Instance block inside main method called without creating an object"); } // Object of 1st kind GFG obj1 = new GFG(); // Object of 2nd kind GFG obj2 = new GFG(); // Object of 3rd kind GFG obj3 = new GFG(); }} |
Output:
C:\Users\Bikash\Desktop\Lazyroar Java>javac GFG.java C:\Users\Bikash\Desktop\Lazyroar Java>java GFG Instance block inside main method called without creating an object Instance block called by creating objects Instance block called by creating objects Instance block called by creating objects
Explanation: It is also possible to execute an instance block without creating an object. To execute an instance block without creating an object we need to define it explicitly inside the main method.