Add NaturalComparator and PathNaturalComparator

app/src/test/java/com/hippo/util/NaturalComparatorTest.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2018 Hippo Seven
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.hippo.util;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class NaturalComparatorTest {
+
+  @Test
+  public void testOrder() {
+    assertOrder("1", "2");
+    assertOrder("2", "11");
+    assertOrder("2", "00011");
+
+    assertOrder("a2", "a11");
+    assertOrder("a2a", "a11a");
+  }
+
+  @Test
+  public void testEquals() {
+    assertEquals("2", "2");
+    assertEquals("11", "11");
+    assertEquals("a11", "a11");
+    assertEquals("a2", "a2");
+    assertEquals("a2a", "a2a");
+  }
+
+  @Test
+  public void testEmpty() {
+    assertOrder("", "1");
+    assertEquals("", "");
+  }
+
+  @Test
+  public void testNull() {
+    assertEquals(null, null);
+    assertOrder(null, "1");
+  }
+
+  private void assertOrder(String s1, String s2) {
+    NaturalComparator comparator = new NaturalComparator();
+    assertTrue(comparator.compare(s1, s2) < 0);
+    assertTrue(comparator.compare(s2, s1) > 0);
+  }
+
+  private void assertEquals(String s1, String s2) {
+    NaturalComparator comparator = new NaturalComparator();
+    Assert.assertEquals(0, comparator.compare(s1, s2));
+    Assert.assertEquals(0, comparator.compare(s2, s1));
+  }
+}