feat: File processing.

src/main/java/eu/ztsh/lfr/model/YearDataAccumulator.java

@@ -0,0 +1,25 @@
+package eu.ztsh.lfr.model;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.DoubleAdder;
+
+public class YearDataAccumulator {
+
+    private final DoubleAdder sum = new DoubleAdder();
+    private final AtomicInteger counter = new AtomicInteger();
+
+    public void add(double value) {
+        synchronized (this) {
+            sum.add(value);
+            counter.incrementAndGet();
+        }
+    }
+
+    public BigDecimal getAverage() {
+        return BigDecimal.valueOf(sum.sum()).setScale(2, RoundingMode.HALF_UP)
+            .divide(BigDecimal.valueOf(counter.get()), RoundingMode.HALF_UP);
+    }
+
+}