add bubblesort

app/src/main/java/de/uni_marburg/powersort/sort/BubbleSort.java

@@ -0,0 +1,49 @@
+package de.uni_marburg.powersort.sort;
+
+import java.util.Comparator;
+
+/**
+ * This utility class provides a method
+ * to sort a list of integers in ascending order.
+ */
+public final class BubbleSort {
+    private BubbleSort() {
+    }
+
+    /**
+     * Algorithm form lecture with addition of early exit if no more swaps occur.
+     */
+    public static <T> void sort(final T[] list, Comparator<T> c) {
+        // Only lists with 2 or more elements need to be sorted.
+        final boolean greaterThan2 = list.length >= 2;
+        if (greaterThan2) {
+            sortGreaterThan2(list, c);
+        }
+    }
+
+    /**
+     * Helper.
+     *
+     * @param list List with >= 2 elements.
+     */
+    private static <T> void sortGreaterThan2(final T[] list, Comparator<T> c) {
+        for (int i = list.length; i >= 1; i--) {
+            boolean swapped = false;
+            for (int j = list.length - 2; j >= 0; j--) {
+                if (c.compare(list[j], list[j + 1]) > 0) {
+                    swap(list, j, j + 1);
+                    swapped = true;
+                }
+            }
+            if (!swapped) {
+                return;
+            }
+        }
+    }
+
+    private static void swap(final Object[] list, final int idx1, final int idx2) {
+        final Object tmp = list[idx1];
+        list[idx1] = list[idx2];
+        list[idx2] = tmp;
+    }
+}