using the string builder

exercises/practice/reverse-string/.approaches/string-builder/content.md

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+# String builder
+
+```clojure
+(defn reverse-string [s]
+  (.toString
+    (.reverse
+      (StringBuilder. s))))
+```
+
+In Clojure, as in Java, strings are immutable.
+It means that with every change we want to make to any string, we create a new string in memory.
+
+String recreation can be very resource-intensive, especially when new strings are created in many steps.
+This is a common problem, so Java provides the `StringBuilder` class, which holds characters as a collection,
+allowing for modifications until we are ready to create the string by calling `toString()` method.
+
+String builder has a built-in `reverse()` method, which we can use as shown above.
+The complete approach is to initialise a `StringBuilder` with the string we want to reverse.
+Then reverse it, and finally convert it back to string.
+
+## The shortcut
+
+Is accessing the underlying Java Virtual Machine and Java classes necessary?
+Couldn't we just use the `clojure.string/reverse` function instead?
+
+We could! This is the alternative way to reverse a string:
+
+```clojure
+(defn reverse-string [s]
+  (clojure.string/reverse s))
+```
+
+In fact, at some level, we could consider both approaches to be equivalent.
+Let's have a look at [the implementation of the `clojure.string/reverse`][implementation] function.
+
+```clojure
+(defn ^String reverse
+  "Returns s with its characters reversed."
+  {:added "1.2"}
+  [^CharSequence s]
+  (.toString (.reverse (StringBuilder. s))))
+```
+
+While there is a little bit more going on in the syntax, at its core, it is the same as the code at the top of this approach.
+
+[implementation]: https://github.com/clojure/clojure/blob/08a2d9bdd013143a87e50fa82e9740e2ab4ee2c2/src/clj/clojure/string.clj#L48C3-L48C3

exercises/practice/reverse-string/.approaches/string-builder/snippet.txt

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+(defn reverse-string [s]
+  (.toString
+    (.reverse
+      (StringBuilder. s))))