Static variables in Java - Step-by-Step Execution

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Concept Flow - Static variables

Class Loaded

↓

Static Variable Created

↓

Objects Created

↓

Objects Share Static Variable

↓

Static Variable Value Changes

↓

All Objects See Updated Value

When a class loads, its static variables are created once and shared by all objects of that class. Changes to static variables affect all instances.

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Execution Sample

Java

class Counter {
  static int count = 0;
  Counter() { count++; }
  static int getCount() { return count; }
}

public class Main {
  public static void main(String[] args) {
    Counter a = new Counter();
    Counter b = new Counter();
    System.out.println(Counter.getCount());
  }
}

This code creates two Counter objects, each increments the shared static count, then prints the total count.

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Execution Table

Step	Action	Static count	Instance created	Output
1	Class Counter loaded, static count initialized to 0	0	No
2	Create object a, constructor increments count	1	a
3	Create object b, constructor increments count	2	b
4	Call Counter.getCount(), returns static count	2	a,b	2

💡 Program ends after printing static count 2

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Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
count (static)	0	1	2	2
a (instance)	null	object created	object created	object created
b (instance)	null	null	object created	object created

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Key Moments - 3 Insights

▶Why does the static variable 'count' keep the total count across all objects?

▶If we create more objects, will 'count' reset for each?

▶Can we access 'count' without creating any objects?

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Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'count' after creating object b (step 3)?

A 1

B 2

C 0

D 3

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Concept Snapshot

Static variables belong to the class, not instances.
They are created once when the class loads.
All objects share the same static variable.
Changes to static variables affect all instances.
Access static variables via ClassName.variable or ClassName.method().

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Full Transcript

Static variables in Java are variables that belong to the class itself, not to any individual object. When the class loads, the static variables are created once and shared by all objects. For example, in the code, the static variable 'count' starts at 0. Each time a new Counter object is created, the constructor increases 'count' by 1. This means all objects see the same 'count' value. After creating two objects, 'count' becomes 2. You can access static variables directly from the class without creating objects. This sharing behavior is useful for keeping track of data common to all instances, like counting how many objects have been made.