JDK 7, also known as Java Development Kit 7, is an older version of the Java Development Kit released by Oracle. It introduced several new features and improvements to the Java programming language and platform. However, it’s important to note that Java 7 has reached its end of life and is no longer officially supported by Oracle. Here are some key features and changes introduced in JDK 7:

1. Language Enhancements:

   • Strings in switch: The switch statement can now use String objects as case values, making it more versatile.
   • Try with Resources: The try-with-resources statement (also known as “automatic resource management”) simplifies resource management by automatically closing resources such as streams, files, and sockets when they are no longer needed.

2. Diamond Operator: The diamond operator (<>) allows you to use type inference when creating instances of generic classes, reducing the need for explicit type declarations.

3. Fork/Join Framework: JDK 7 introduced the Fork/Join Framework, a concurrency framework for parallel programming that simplifies the development of multi-threaded applications.

4. Improved Exception Handling: JDK 7 introduced multi-catch and rethrowing exceptions, making exception handling more flexible and concise.

5. New File I/O and NIO.2: The new File I/O and NIO.2 (New I/O) APIs provide enhanced support for file and file system operations, including asynchronous file I/O.

6. Support for Dynamic Languages: JDK 7 introduced the InvokeDynamic bytecode instruction, which improved support for dynamic languages like JavaScript and Ruby on the Java Virtual Machine (JVM).

7. Performance Improvements: JDK 7 included various performance enhancements, including the G1 Garbage Collector, which was made available as an experimental feature.

8. Project Coin: Project Coin was an umbrella project for small language enhancements in JDK 7, which aimed to improve the readability and maintainability of Java code. Some of these enhancements included try-with-resources, the diamond operator, and the underscore as a variable name.

9. Removal of PermGen Space: JDK 7 started the process of removing the Permanent Generation (PermGen) space and introduced the Metaspace to store class metadata.

It’s worth noting that while JDK 7 introduced many improvements, it is considered outdated, and security updates are no longer provided. For development and production use, it’s recommended to use a more recent version of Java, such as Java 8 (a long-term support version) or a newer release. These newer versions offer improved performance, security, and language features.