Online Java Compiler — Compile & Run Java 21
CodePocket provides an online Java compiler powered by OpenJDK 21 LTS. Practice object-oriented design, data structures, Streams API, and competitive programming with zero local JDK installation.
> Output (32ms): Java 21 Streams Output: [SARAH, ELENA, DAVID, MARCUS] > [Process exited with code 0]
Why use CodePocket for Java Development?
CodePocket provides an isolated, zero-configuration cloud container environment for writing and running Java code. Whether you are learning core language fundamentals, preparing for technical coding interviews, or testing algorithm prototypes, CodePocket delivers instant execution feedback without local setup.
OpenJDK 21 LTS Features
Support for record patterns, pattern matching for switch, sequenced collections, and virtual threads.
Interactive Scanner & STDIN
Read dynamic user inputs using java.util.Scanner with real-time terminal stream feedback.
Full Collections Framework
Access ArrayList, HashMap, PriorityQueue, LinkedList, and the Java Streams API.
Common Java Errors & Quick Fixes
Cause: The public class name does not match the file name.
Fix: Keep the main class named public class Main or remove public from class definition.
Cause: Attempting to call methods or access properties on an object reference that is null.
Fix: Ensure objects are initialized before invocation or check if (obj != null).
Cause: Using an undeclared variable, misspelled method, or forgetting import statements.
Fix: Import required packages like import java.util.*; and check spelling.