Static blocks in Java - Step-by-Step Execution

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Concept Flow - Static blocks

Class Load Start

↓

Static Variables Initialized

↓

Execute Static Block

↓

Class Ready for Use

↓

Main Method or Object Creation

When the class loads, the static block runs once to initialize static variables before any object is created or main runs.

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Execution Sample

Java

class Test {
  static int x;
  static {
    x = 5;
    System.out.println("Static block runs");
  }
  public static void main(String[] args) {
    System.out.println(x);
  }
}

This code runs the static block once when the class loads, sets x to 5, then prints x in main.

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Execution Table

Step	Action	Static Variable x	Output
1	Class loads, static variables initialized	0
2	Static block runs, sets x to 5	5	Static block runs
3	Main method starts, print x	5	5
4	Program ends	5

💡 Program ends after main method finishes

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Variable Tracker

Variable	Start	After Static Block	After Main
x	0 (default)	5	5

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Key Moments - 3 Insights

▶Why does the static block run before main?

▶Does the static block run again if we create objects?

▶What is the initial value of static int x before the static block?

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Visual Quiz - 3 Questions

Look at the execution table, what is the value of x after the static block runs?

A 0

B Undefined

C 5

D 10

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Concept Snapshot

Static blocks run once when the class loads.
They initialize static variables.
Run before main or any object creation.
Syntax: static { /* code */ }
Useful for setup tasks.
Runs only once per class load.

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Full Transcript

Static blocks in Java run once when the class is loaded by the JVM. This happens before the main method starts or any objects are created. In the example, the static block sets the static variable x to 5 and prints a message. The variable x starts with a default value of 0, then changes to 5 after the static block runs. The main method then prints the value of x. Static blocks are useful to initialize static variables or run setup code. They do not run again if multiple objects are created.