StringBuilder and StringBuffer in Java - Practice Problems & Coding Challenges

trophy

Challenge - 5 Problems

💻 code output

intermediate

Output of StringBuilder append operations

What is the output of the following Java code snippet?

Java

StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");
sb.append('!');
System.out.println(sb.toString());

A !dlroW olleH

B Hello World

C HelloWorld!

D Hello World!

💻 code output

intermediate

Thread safety difference between StringBuilder and StringBuffer

What will happen if multiple threads modify a StringBuffer and a StringBuilder concurrently without synchronization?

A StringBuffer operations are thread-safe; StringBuilder operations may cause data corruption.

B Neither StringBuffer nor StringBuilder is thread-safe.

C Both StringBuffer and StringBuilder are thread-safe.

D StringBuilder is thread-safe; StringBuffer is not.

🔧 debug

advanced

Identify the error in StringBuilder usage

What error will the following code produce?

Java

StringBuilder sb = null;
sb.append("Test");

A NullPointerException

B StringIndexOutOfBoundsException

C No error, prints 'Test'

D Compilation error

📝 syntax

advanced

Correct way to convert StringBuilder to String

Which option correctly converts a StringBuilder object to a String?

Java

StringBuilder sb = new StringBuilder("example");

A String s = (String) sb;

B String s = sb.convert();

C String s = sb.toString();

D String s = sb.stringValue();

🚀 application

expert

Predict the final content after multiple StringBuffer operations

Given the following code, what is the final output?

Java

StringBuffer sb = new StringBuffer("Start");
sb.insert(5, " Middle");
sb.replace(0, 5, "Begin");
sb.delete(6, 13);
System.out.println(sb.toString());

A nigeB

B Begin

C Begin Middle

D Start Middle