Of course. Here is a comprehensive overview of the Java API 1.7, presented in English.

Java API 1.7 (Java 7) Overview

Java 7, codenamed Dolphin, was a major release that introduced several significant new features to the Java language and its core APIs. While the language features (like the diamond operator and try-with-resources) are highly visible, the API enhancements were equally important, adding new functionality and improving existing libraries.

This document covers the key additions and changes to the Java API in version 1.7.

New Packages and Major API Additions

a. java.nio.file Package (The New I/O API)

This was arguably the most significant addition in Java 7. It provided a more powerful, flexible, and scalable way to interact with the file system compared to the legacy java.io.File package.

Key Classes and Interfaces:

• Path: Represents a path in the file system. It's the central interface, replacing many of the methods in java.io.File. It's an object that can be used to locate a file or directory.

  • Example: Path path = Paths.get("/home/user/docs/report.txt");

• Paths: A utility class with static factory methods (get()) to easily create Path objects.

• Files: A utility class with static methods for performing common file operations, such as reading, writing, copying, deleting, and checking file attributes.

  • Reading all lines of a file into a List: List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);
  • Writing a string to a file: Files.write(path, "Hello, World!".getBytes(StandardCharsets.UTF_8));

• FileSystem: Represents the file system itself. It allows you to access file stores, watch for changes, and create other Path objects.

  
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• FileStore: Represents a storage volume (like a hard drive or partition). You can query it for space information.

• WatchService: A powerful mechanism for monitoring a directory (or a file) for changes (e.g., creation, deletion, modification). This is done by registering a WatchKey with a WatchService.

  // Example of watching a directory for changes
  WatchService watchService = FileSystems.getDefault().newWatchService();
  Path path = Paths.get("/path/to/directory");
  path.register(watchService, StandardWatchEventKinds.ENTRY_CREATE,
                          StandardWatchEventKinds.ENTRY_DELETE,
                          StandardWatchEventKinds.ENTRY_MODIFY);
  WatchKey key;
  while ((key = watchService.take()) != null) {
      for (WatchEvent<?> event : key.pollEvents()) {
          System.out.println("Event kind: " + event.kind() + ". File affected: " + event.context() + ".");
      }
      key.reset();
  }

b. java.util.concurrent Package Enhancements

The concurrency library received several useful additions to make concurrent programming easier.

• ForkJoinPool and RecursiveTask / RecursiveAction: These classes form the basis of the Fork/Join Framework. It's designed for work that can be broken down into smaller pieces, processed in parallel, and then combined. This is highly efficient for "divide and conquer" algorithms.

  • ForkJoinPool: The executor service that manages the worker threads.
  • RecursiveTask: A task that returns a result.
  • RecursiveAction: A task that does not return a result.

• TransferQueue: A new interface in the java.util.concurrent package. It's an extension of BlockingQueue where a producer can wait until a consumer receives the data. The transfer() method is the key addition.

• ForkJoinPool.commonPool(): A static method to get the common pool for the entire JVM, simplifying its use for applications.

c. java.lang.invoke Package (Method Handles and InvokeDynamic)

This was a highly advanced and low-level addition, primarily for use by language implementers (like the Java compiler itself) and frameworks. It provides a dynamic alternative to reflection for method and constructor invocation.

• MethodHandle: A typed, directly executable reference to a method, constructor, or field. It's more efficient and flexible than reflection.
• MethodHandles: A factory class for creating MethodHandle instances.
• CallSite and invokedynamic: The invokedynamic bytecode instruction is used to create dynamic call sites. A CallSite holds a MethodHandle that can be changed dynamically. This was the foundation for implementing dynamic languages like Groovy and JRuby on the JVM.

d. java.util.Objects Class

A small but extremely useful utility class containing static utility methods to operate on objects. It helps in writing null-safe code.

• requireNonNull(T obj): Throws a NullPointerException if the object is null. Perfect for validating method arguments.
  • Example: public void setName(String name) { this.name = Objects.requireNonNull(name); }
• equals(Object a, Object b): A null-safe equality check. It returns true if both are null, or if they are equal.
• hashCode(Object o): A null-safe hash code calculation. Returns 0 if the object is null.
• toString(Object o): A null-safe toString method. Returns "null" if the object is null.

e. java.time Package (The New Date and Time API)

Note: The full java.time package was introduced in Java 8. However, Java 7 introduced a smaller, related package: java.time.chrono. This package contained support for calendar systems other than the default ISO-8601 calendar, such as the Japanese Imperial Calendar and Thai Buddhist Calendar. This was a preparatory step for the much larger and more comprehensive java.time API in Java 8.

Enhanced APIs (Existing Packages)

a. java.lang.AutoCloseable Interface

This interface was added to the language to support the try-with-resources statement. Any resource that needs to be closed (like files, streams, database connections) should implement this interface. The close() method is automatically called when the try block is exited, either normally or due to an exception.

• Existing classes retrofitted: Many existing classes in java.io and java.nio.channels were updated to implement AutoCloseable.
  • java.io.InputStream
  • java.io.OutputStream
  • java.io.Reader
  • java.io.Writer
  • java.nio.channels.Channel

b. java.lang.ThreadLocalRandom Class

A more efficient and convenient way to generate random numbers in a multi-threaded environment. It provides a thread-local version of java.util.Random, avoiding the contention that can occur when multiple threads access a shared Random instance.

• Usage: int randomNum = ThreadLocalRandom.current().nextInt(1, 10);

c. java.util.NavigableMap and java.util.NavigableSet Enhancements

These interfaces (which are implemented by TreeMap and TreeSet) got new methods to make navigation more convenient:

• pollFirstEntry() / pollLastEntry(): Removes and returns the first/last key-value pair from a map.
• replace(K key, V oldValue, V newValue): Atomically replaces the value for a key only if it is currently mapped to a given value.

Deprecated and Removed APIs

• Deprecated: The java.util.concurrent.ConcurrentHashMap's old() method was deprecated. Many older, less secure methods in various packages were also deprecated.
• Removed: The com.sun packages, which contained internal, proprietary APIs not intended for public use, were no longer part of the standard distribution. Code that relied on these would break.

Summary of Key API Changes in Java 7

For the complete and authoritative reference, you should always consult the official Java SE 7 Documentation from Oracle.