When is static block executed in java

This approach works well when you know the initial value. If initialization requires some logic for example some conditional statements or exception handling , this approach is not sufficient.

That is where initialization blocks are quite useful. There are two types of initializer blocks in java :. These blocks are generally used to initialize static or class variables. A static initializer block is also known as static block. The syntax of declaring a static block is :. As soon as your class is loaded by java virtual machine , all static blocks given inside your class is executed.

As you can see from the output, static blocks are executed from top to bottom. It is executed even before main method is executed. You have a static method which is using value of static variable serverUrl. If static method executed before static block then there will not be server url value assigned to the static variable serverUrl you will get default value and not the value from the static block.

To avoid this problem static block always gets executed before static method to ensure that the static variables will get value before their use. If you use a static method to initialize static variable then there is no guarantee that the static method will execute before executing other methods and assign value to the static variable before its use.

Instead static initalizer block always execute before all methods therefore there is guarantee that instance variables get value before their use. Previous Topic. Next Topic.

Rules and Uses of Static Initializer Block in Java With Example Static block also called initializer block is mostly used for changing the default values of static variables. Static block cannot return a value. Static block cannot be called explicitly. Static block cannot throws an exception.

However, order does matter between an initialization block and a field initializer. In your code the parent static blocks will be executed first and then the child class static blocks. Static block in java is executed before main method. If we declare a Static block in java class it is executed when class loads.

This is initialize with the static variables. It is mostly used in JDBC. Static block in java is executed every time when a class loads. This is also known as Static initialization block. Static block in java initializes when class load into memory , it means when JVM read the byte code.

Initialization can be anything; it can be variable initialization or anything else which should be shared by all objects of that class. It would be very helpful to ckeck out the object construction process with a step by step debuger, having a view in which you can see how your object is goning through the phases.

I found this very useful for clearing the perspective from a higher point of view. Eclipse can help you with this with it's debugger step into function. Just wanted to share my findings. I read in one of the answers on another thread that static blocks are executed first before static fields which is not correct.

It depends on which comes first, static field or static block. Have a look at below code. It will try to put things in perspective. If multiple static blocks are there, it will execute it in the order in which it appears,.

Static block gets executed when a class is loaded into JVM. While init block gets copied into the Constructor whose object will be created and runs before creation of object.

JVM Load this class. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. In what order do static blocks and initialization blocks execute when using inheritance?

Ask Question. Asked 8 years ago. Active 11 months ago. Viewed 88k times. With the newer version of Java 1. Add a comment. Active Oldest Votes. Ky Leggiero Ky Leggiero Please accompany any downvotes with a reason, so I know how to write better answers in the future : — Ky Leggiero. Your output doesn't disprove this.