Object lifetime in Java - Step-by-Step Execution

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Concept Flow - Object lifetime

Create Object with new

↓

Object exists in heap

↓

Reference variable points to object

↓

Use object via reference

↓

Reference set to null or goes out of scope

↓

No references to object

↓

Garbage Collector removes object

↓

Memory freed

This flow shows how an object is created, used, and then removed when no references point to it.

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Execution Sample

Java

public class Demo {
    public static void main(String[] args) {
        String s = new String("Hello");
        s = null;
    }
}

This code creates a String object, then removes the reference, making the object eligible for garbage collection.

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Execution Table

Step	Action	Reference Variable 's'	Object in Heap	Garbage Collection Eligible
1	Create new String object	Points to new String("Hello")	String("Hello") created	No
2	Assign null to s	null	String("Hello") still exists	Yes
3	End of main method	null	String("Hello") still exists	Yes

💡 Program ends, object without references is eligible for garbage collection.

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Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
s	undefined	points to String("Hello")	null	null

key

Key Moments - 3 Insights

▶Why does the object still exist after setting the reference to null?

▶Does setting the reference to null immediately delete the object?

▶What happens if there are multiple references to the same object?

psychology

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 's' after step 1?

A undefined

B null

C points to String("Hello")

D Garbage collected

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Concept Snapshot

Object lifetime in Java:
- Objects created with 'new' live in heap memory.
- Reference variables point to objects.
- When references are set to null or go out of scope, objects become unreachable.
- Garbage Collector removes unreachable objects to free memory.
- Object removal timing is managed by JVM, not immediate on null assignment.

contract

Full Transcript

In Java, when you create an object using 'new', it is stored in heap memory. A reference variable points to this object. You can use the object through this reference. When you set the reference to null or it goes out of scope, the object no longer has any references pointing to it. At this point, the object becomes eligible for garbage collection. The Java Garbage Collector will then remove the object from memory to free space. This process is automatic and happens sometime after the object becomes unreachable, not immediately when the reference is set to null.