Use list-head-tail (#64)

The HeadTail interface has been extracted to its own project for reuse.

pom.xml

@@ -22,6 +22,7 @@
         <tiles-maven-plugin.version>2.16</tiles-maven-plugin.version>
         <kemitix-maven-tiles.version>2.4.1</kemitix-maven-tiles.version>
         <kemitix-checkstyle.version>5.4.0</kemitix-checkstyle.version>
+        <list-head-tail.version>1.0.0</list-head-tail.version>
         <lombok.version>1.18.12</lombok.version>
         <assertj.version>3.15.0</assertj.version>
         <trajano-commons-testing.version>2.1.0</trajano-commons-testing.version>
@@ -46,6 +47,11 @@
     <inceptionYear>2016</inceptionYear>
 
     <dependencies>
+        <dependency>
+            <groupId>net.kemitix</groupId>
+            <artifactId>list-head-tail</artifactId>
+            <version>${list-head-tail.version}</version>
+        </dependency>
         <dependency>
             <groupId>org.projectlombok</groupId>
             <artifactId>lombok</artifactId>

src/main/java/net/kemitix/node/HeadTail.java

@@ -1,62 +0,0 @@
-/**
- * The MIT License (MIT)
- *
- * Copyright (c) 2018 Paul Campbell
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
- * and associated documentation files (the "Software"), to deal in the Software without restriction,
- * including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
- * and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
- * subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all copies
- * or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
- * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
- * AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
- * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
-package net.kemitix.node;
-
-import java.util.Collections;
-import java.util.List;
-import java.util.Optional;
-
-/**
- * Provides a simple implementation of head() and tail() for {@link List}s.
- */
-public interface HeadTail {
-
-    /**
-     * Returns the first item in the list as an {@link Optional}.
-     *
-     * @param list the list
-     * @param <X> the type of the lists contents
-     * @return an Optional containing the first item in the list, or empty if
-     * the list is empty.
-     */
-    static <X> Optional<X> head(final List<X> list) {
-        if (list.isEmpty()) {
-            return Optional.empty();
-        }
-        return Optional.ofNullable(list.get(0));
-    }
-
-    /**
-     * Returns the list, minus the first item.
-     *
-     * @param list the list
-     * @param <X> the type of the lists contents
-     * @return a view of the list starting with the second item, or an empty
-     * list if the original list has less than two items.
-     */
-    static <X> List<X> tail(final List<X> list) {
-        if (list.size() < 1) {
-            return Collections.emptyList();
-        }
-        return list.subList(1, list.size());
-    }
-}

src/main/java/net/kemitix/node/NodeItem.java

@@ -30,8 +30,8 @@ import java.util.*;
 import java.util.function.Function;
 import java.util.stream.Stream;
 
-import static net.kemitix.node.HeadTail.head;
-import static net.kemitix.node.HeadTail.tail;
+import static net.kemitix.list.HeadTail.head;
+import static net.kemitix.list.HeadTail.tail;
 
 /**
  * Represents a tree of nodes.

src/test/java/net/kemitix/node/HeadTailTest.java

@@ -1,53 +0,0 @@
-package net.kemitix.node;
-
-import org.junit.jupiter.api.Test;
-
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.List;
-import java.util.UUID;
-
-import static net.kemitix.node.HeadTail.head;
-import static net.kemitix.node.HeadTail.tail;
-import static org.assertj.core.api.Assertions.assertThat;
-
-public class HeadTailTest {
-
-    private String headValue = "1-" + UUID.randomUUID().toString();
-    private String secondValue = "2-" +  UUID.randomUUID().toString();
-    private String thirdValue = "3-" + UUID.randomUUID().toString();
-    private List<String> emptyList = Collections.emptyList();
-    private List<String> singletonList = Collections.singletonList(headValue);
-    private List<String> aList = Arrays.asList(
-            headValue, secondValue, thirdValue
-    );
-    private List<String> tailValue = Arrays.asList(
-            secondValue, thirdValue
-    );
-
-    @Test
-    public void headOfAnEmptyListIsEmpty() {
-        assertThat(head(emptyList)).isEmpty();
-    }
-    @Test
-    public void headOfASingletonListIsTheItem() {
-        assertThat(head(singletonList)).contains(headValue);
-    }
-    @Test
-    public void headOfAListIsTheFirstItem() {
-        assertThat(head(aList)).contains(headValue);
-    }
-
-    @Test
-    public void tailOfAnEmptyListIsEmpty() {
-        assertThat(tail(emptyList)).isEmpty();
-    }
-    @Test
-    public void tailOfASingletonListIsEmpty() {
-        assertThat(tail(singletonList)).isEmpty();
-    }
-    @Test
-    public void tailOfAListIsMinusTheHead() {
-        assertThat(tail(aList)).isEqualTo(tailValue);
-    }
-}