String vs StringBuilder in Java - Visual Side-by-Side Comparison

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Concept Flow - String vs StringBuilder

Create String or StringBuilder

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Modify content?

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String: create new String

↓

Use updated value

↓

End

Shows how String creates new objects on change, while StringBuilder modifies content without new objects.

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Execution Sample

Java

String s = "Hi";
s = s + "!";

StringBuilder sb = new StringBuilder("Hi");
sb.append("!");

System.out.println(s);
System.out.println(sb.toString());

This code shows adding "!" to a String and a StringBuilder, then prints both.

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Execution Table

Step	Variable	Action	Value After Action	Notes
1	s	Initialize with "Hi"	"Hi"	String s points to "Hi"
2	s	Concatenate "!" to s	"Hi!"	New String created, s points to "Hi!"
3	sb	Create StringBuilder with "Hi"	StringBuilder("Hi")	sb holds mutable sequence "Hi"
4	sb	Append "!" to sb	StringBuilder("Hi!")	sb content changed in place
5	s	Print s	"Hi!"	Outputs Hi!
6	sb	Print sb.toString()	"Hi!"	Outputs Hi!
7	-	End of program	-	Execution stops

💡 Program ends after printing both values.

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Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
s	"Hi"	"Hi!"	"Hi!"	"Hi!"
sb	null	null	StringBuilder("Hi!")	StringBuilder("Hi!")

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Key Moments - 3 Insights

▶Why does String s change reference after concatenation?

▶Does StringBuilder create a new object when appending?

▶Why do both s and sb print the same output even though they behave differently?

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Visual Quiz - 3 Questions

Look at the execution_table, what is the value of s after step 2?

A "Hi"

B null

C "Hi!"

D "!"

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Concept Snapshot

String vs StringBuilder in Java:
- String is immutable; changes create new objects.
- StringBuilder is mutable; changes happen in place.
- Use StringBuilder for many modifications to improve performance.
- String concatenation creates new Strings each time.
- StringBuilder has append() method to add content efficiently.

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Full Transcript

This visual trace compares Java String and StringBuilder. Initially, String s is "Hi". When concatenated with "!", a new String "Hi!" is created and s points to it. StringBuilder sb starts with "Hi" and appends "!" by modifying its content in place. Both print "Hi!" at the end. Key points: String is immutable and creates new objects on change; StringBuilder is mutable and changes content without new objects. This helps understand performance and behavior differences.