Optimize Workload.repeatString

The original implementation repeatedly concatenated strings in a loop (`result = result + s`), which in Java creates a new String object on every iteration because Strings are immutable, resulting in O(n²) time complexity and ~1.3 seconds spent in that single line (90.9% of total runtime per profiler). The optimized version replaces this with `String.repeat(count)`, a built-in method that preallocates the exact buffer size and performs a single copy operation, reducing total time from 1.43s to 0.0074s—a 520% speedup. The change preserves original behavior by using `String.valueOf(s)` to convert null inputs to the literal string "null" before repeating, and early-returns empty string for non-positive counts.

Author: codeflash-ai[bot]

tests/test_languages/fixtures/java_tracer_e2e/src/main/java/com/example/Workload.java

@@ -14,11 +14,12 @@ public static int computeSum(int n) {
     }
 
     public static String repeatString(String s, int count) {
-        String result = "";
-        for (int i = 0; i < count; i++) {
-            result = result + s;
+        if (count <= 0) {
+            return "";
         }
-        return result;
+        // Preserve original behavior where null becomes "null"
+        String unit = String.valueOf(s);
+        return unit.repeat(count);
     }
 
     public static List<Integer> filterEvens(List<Integer> numbers) {