class InterviewBit{ INT i; static int J; { System.out.println(" Instance Block 1. Value of i = "+i); } static{ System.out.println(" Static Block 1. Value of j = "+j); method_2(); } { i = 5; } static{ j = 10; } InterviewBit(){ System.out.println(" Welcome to InterviewBit "); } public static void main(String[] args){ InterviewBit ib = new InterviewBit(); } public void method_1(){ System.out.println(" Instance method. "); } static{ System.out.println(" Static Block 2. Value of j = "+j); } { System.out.println(" Instance Block 2. Value of i = "+i); method_1(); } public static void method_2(){ System.out.println(" Static method. "); }}

The Output we get by executing this program will be

Static Block 1. Value of j = 0
Static method. 
Static Block 2. Value of j = 10
Instance Block 1. Value of i = 0
Instance Block 2. Value of i = 5
Instance method. 
Welcome to InterviewBit

This is a java tricky interview question frequently asked in java interviews for the EXPERIENCED. The output will be like this because, when the java program is compiled and gets executed, then there are various steps followed for execution. And the steps are - 

• Identification of Static Members from top to bottom.
• Execution of Static variable assignment and a Static block from top to bottom.
• Execution of the main method.
• Identification of Instance Members from top to bottom.
• Execution of Instance variable assignment and Instance block from top to bottom.
• Execution of Constructor.

In above steps from 4 to 6, will be executed for EVERY object creation. If we create multiple objects then for every object these steps will be performed.

Now from the above code, the execution will happen like this - 

1. In the step of identification of static members. It is found that -

• static int j.
• static block.
• main method.
• static method_2.

During identification, the JVM will assign the default value in the static int j variable. Then it is currently in the state of reading and indirectly writing. Because the original value is not assigned.

2. In the next step, it will execute the static block and assign the value in static variables.

• First static block it will print and because execution from top to bottom and original value in j is not assigned. So it will print the default value of 0.
• After executing static block 1. It will execute the static method_1 because it is called from the static block 1.
• Then it will assign the original value of 5 in the j variable. And executes the remaining static block.

3. Now it will execute the main method. In which it will create an object for the class InterviewBit. And then the execution of INSTANCES will happen.

4. Identify the instance variables and blocks from top to bottom. 

• int i.
• Instance block 1.
• Instance method_1.

Like a static variable, the instance variable also has been initialized with the default value 0 and will be in the state of reading and writing indirectly.

5. It will execute the instance methods and assign the original value to the instance variable.

• Prints the Instance block 1. And the current value of i is not assigned till now, so it will print 0.
• Assign the original value to i. Then print instance block 2. And after that instance method will be called and printed because it is being called in the instance block.

6. And at the last step, the constructor will be invoked and the lines will be executed in the constructor.

This is how the java program gets executed.