Java Development Kit (JDK) 7 is a version of the Java Development Kit released by Oracle. It introduced several new features and improvements to the Java programming language and platform. Here are some key features and changes introduced in JDK 7:

1. Strings in Switch: JDK 7 introduced the ability to use strings in the switch statement. This means you can switch on a string value, making your code more expressive when dealing with string-based conditions.

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   String fruit = "apple";
switch (fruit) {
case "apple":
System.out.println("It's an apple.");
break;
case "banana":
System.out.println("It's a banana.");
break;
default:
System.out.println("Unknown fruit.");
break;
}


2. Try-With-Resources: The try-with-resources statement was introduced to simplify resource management. It allows you to automatically close resources like streams, files, and sockets at the end of a try block, reducing the need for explicit finally blocks.

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   try (BufferedReader reader = new BufferedReader(new FileReader("file.txt"))) {
String line = reader.readLine();
// Process the data
} catch (IOException e) {
e.printStackTrace();
}


3. Diamond Operator: JDK 7 introduced the diamond operator (<>), which allows you to omit the explicit type declaration when creating instances of generic classes. This enhances code readability.

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   List<String> names = new ArrayList<>();


4. Fork/Join Framework: JDK 7 introduced the Fork/Join Framework, a powerful concurrency framework for parallel processing. It simplifies the development of multi-threaded applications by providing a high-level API for dividing tasks among multiple threads.

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

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   try {
// Code that may throw exceptions
} catch (IOException | SQLException e) {
// Handle multiple exception types
}


6. 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.

7. 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).

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

9. 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.

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

Java 7 was a significant release that introduced several language enhancements and performance improvements, making it a noteworthy milestone in the evolution of the Java platform. However, it’s essential to note that Java 7 reached its end of life and is no longer officially supported by Oracle. For development and production use, it’s recommended to use a more recent version of Java, such as Java 8, Java 11, or a newer release, which offer improved features and security updates.