Java and C# are both commonly used programming languages. While Java was historically dominant, C# has gained popularity with new features. Both are object-oriented, high-level languages that can handle large data and scale well. However, Java was designed to execute on any Java platform using JRE, while C# was designed to run on .NET framework. Java is generally used more for messaging, web apps, and concurrent apps, while C# is more common for games, mobile development and virtual reality. They also differ in data types, with Java having primitive types and C# using simple value types.