docs: parallelStream hyperlink add

exercises/practice/parallel-letter-frequency/.approaches/introduction.md

@@ -10,11 +10,11 @@ A [`map`][map], being a key-value pair structure, is suitable for recording freq
 If the data being counted has a limited range (e.g., `Characters` or `Integers`), an `int[] array` or [`List<Integer>`][list] can be used to record frequencies.
 
 Parallel processing typically takes place in a multi-[`thread`][thread] environment.
-The Java 8 [`stream`][stream] API provides methods that make parallel processing easier, including the `parallelStream()` method.
-With `parallelStream()`, developers can use the [`ForkJoinPool`][ForkJoinPool] model for workload division and parallel execution, without the need to manually manage threads or create custom thread pools.
+The Java 8 [`stream`][stream] API provides methods that make parallel processing easier, including the [`parallelStream()`][stream] method.
+With [`parallelStream()`][stream], developers can use the [`ForkJoinPool`][ForkJoinPool] model for workload division and parallel execution, without the need to manually manage threads or create custom thread pools.
 
 The [`ForkJoinPool`][ForkJoinPool] class, optimized for dividing and managing tasks, makes parallel processing efficient.
-However, `parallelStream()` uses the common [`ForkJoinPool`][ForkJoinPool] by default, meaning multiple `parallelStream` instances share the same thread pool unless configured otherwise.  
+However, [`parallelStream()`][stream] uses the common [`ForkJoinPool`][ForkJoinPool] by default, meaning multiple [`parallelStream`][stream] instances share the same thread pool unless configured otherwise.  
 
 As a result, parallel streams may interfere with each other when sharing this thread pool, potentially affecting performance.
 Although this doesn’t directly impact solving the Parallel Letter Frequency problem, it may introduce issues when thread pool sharing causes conflicts in other applications.  
@@ -130,7 +130,7 @@ For more information, check the [`fork/join` approach][approach-fork-join].
 
 ## Which approach to use?
 
-When tasks are simple or do not require a dedicated thread pool (such as in this case), the `parallelStream` approach is recommended.
+When tasks are simple or do not require a dedicated thread pool (such as in this case), the [`parallelStream`][stream] approach is recommended.
 However, if the work is complex or there is a need to isolate thread pools from other concurrent tasks, the [`ForkJoinPool`][ForkJoinPool] approach is preferable.
 
 [thread]: https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html