new appendix

collectiontopics/Bits.java

@@ -14,7 +14,7 @@ public class Bits {
     System.out.println("bit pattern: " + bbits);
   }
   public static void main(String[] args) {
-    SplittableRandom rand = new SplittableRandom(47);
+    Random rand = new Random(47);
     // Take the LSB of nextInt():
     byte bt = (byte)rand.nextInt();
     BitSet bb = new BitSet();

collectiontopics/CanonicalMapping.java

@@ -11,7 +11,9 @@ class Element {
   @Override
   public String toString() { return ident; }
   @Override
-  public int hashCode() { return ident.hashCode(); }
+  public int hashCode() {
+    return Objects.hashCode(ident);
+  }
   @Override
   public boolean equals(Object r) {
     return r instanceof Element &&

collectiontopics/Prediction.java

@@ -1,18 +0,0 @@
-// collectiontopics/Prediction.java
-// (c)2017 MindView LLC: see Copyright.txt
-// We make no guarantees that this code is fit for any purpose.
-// Visit http://OnJava8.com for more book information.
-// Predicting the weather with groundhogs
-import java.util.*;
-
-public class Prediction {
-  private static SplittableRandom rand = new SplittableRandom(47);
-  private boolean shadow = rand.nextDouble() > 0.5;
-  @Override
-  public String toString() {
-    if(shadow)
-      return "Six more weeks of Winter!";
-    else
-      return "Early Spring!";
-  }
-}

collectiontopics/SpringDetector.java

@@ -1,39 +0,0 @@
-// collectiontopics/SpringDetector.java
-// (c)2017 MindView LLC: see Copyright.txt
-// We make no guarantees that this code is fit for any purpose.
-// Visit http://OnJava8.com for more book information.
-// What will the weather be?
-import java.lang.reflect.*;
-import java.util.*;
-
-public class SpringDetector {
-  // Uses a Groundhog or class derived from Groundhog:
-  public static <T extends Groundhog>
-  void detectSpring(Class<T> type) throws Exception {
-    Constructor<T> ghog = type.getConstructor(int.class);
-    Map<Groundhog,Prediction> map = new HashMap<>();
-    for(int i = 0; i < 10; i++)
-      map.put(ghog.newInstance(i), new Prediction());
-    System.out.println("map = " + map);
-    Groundhog gh = ghog.newInstance(3);
-    System.out.println("Looking up prediction for " + gh);
-    if(map.containsKey(gh))
-      System.out.println(map.get(gh));
-    else
-      System.out.println("Key not found: " + gh);
-  }
-  public static void
-  main(String[] args) throws Exception {
-    detectSpring(Groundhog.class);
-  }
-}
-/* Output:
-map = {Groundhog #2=Early Spring!, Groundhog #5=Early
-Spring!, Groundhog #6=Early Spring!, Groundhog #4=Early
-Spring!, Groundhog #9=Six more weeks of Winter!, Groundhog
-#8=Six more weeks of Winter!, Groundhog #0=Early Spring!,
-Groundhog #1=Early Spring!, Groundhog #3=Early Spring!,
-Groundhog #7=Six more weeks of Winter!}
-Looking up prediction for Groundhog #3
-Key not found: Groundhog #3
-*/

collectiontopics/SpringDetector2.java

@@ -1,22 +0,0 @@
-// collectiontopics/SpringDetector2.java
-// (c)2017 MindView LLC: see Copyright.txt
-// We make no guarantees that this code is fit for any purpose.
-// Visit http://OnJava8.com for more book information.
-// A working key
-
-public class SpringDetector2 {
-  public static void
-  main(String[] args) throws Exception {
-    SpringDetector.detectSpring(Groundhog2.class);
-  }
-}
-/* Output:
-map = {Groundhog #0=Early Spring!, Groundhog #1=Early
-Spring!, Groundhog #2=Early Spring!, Groundhog #3=Early
-Spring!, Groundhog #4=Early Spring!, Groundhog #5=Early
-Spring!, Groundhog #6=Early Spring!, Groundhog #7=Six more
-weeks of Winter!, Groundhog #8=Six more weeks of Winter!,
-Groundhog #9=Six more weeks of Winter!}
-Looking up prediction for Groundhog #3
-Early Spring!
-*/

equalshashcode/ComposedEquality.java

@@ -1,4 +1,4 @@
-// collectiontopics/ComposedEquality.java
+// equalshashcode/ComposedEquality.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.

equalshashcode/CountedString.java

@@ -1,4 +1,4 @@
-// collectiontopics/CountedString.java
+// equalshashcode/CountedString.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.
@@ -41,8 +41,7 @@ public class CountedString {
       Objects.equals(id, ((CountedString)o).id);
   }
   public static void main(String[] args) {
-    Map<CountedString,Integer> map =
+    Map<CountedString,Integer> map = new HashMap<>();
-      new HashMap<>();
     CountedString[] cs = new CountedString[5];
     for(int i = 0; i < cs.length; i++) {
       cs[i] = new CountedString("hi");

equalshashcode/DefaultComparison.java

@@ -0,0 +1,24 @@
+// equalshashcode/DefaultComparison.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+
+class DefaultComparison {
+  private int i, j, k;
+  public DefaultComparison(int i, int j, int k) {
+    this.i = i;
+    this.j = j;
+    this.k = k;
+  }
+  public static void main(String[] args) {
+    DefaultComparison
+      a = new DefaultComparison(1, 2, 3),
+      b = new DefaultComparison(1, 2, 3);
+    System.out.println(a == a);
+    System.out.println(a == b);
+  }
+}
+/* Output:
+true
+false
+*/

equalshashcode/Equality.java

@@ -1,4 +1,4 @@
-// collectiontopics/Equality.java
+// equalshashcode/Equality.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.

equalshashcode/EqualityFactory.java

@@ -1,4 +1,4 @@
-// collectiontopics/EqualityFactory.java
+// equalshashcode/EqualityFactory.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.

equalshashcode/Groundhog.java

@@ -1,4 +1,4 @@
-// collectiontopics/Groundhog.java
+// equalshashcode/Groundhog.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.

equalshashcode/Groundhog2.java

@@ -1,4 +1,4 @@
-// collectiontopics/Groundhog2.java
+// equalshashcode/Groundhog2.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.

equalshashcode/IndividualTest.java

@@ -1,4 +1,4 @@
-// collectiontopics/IndividualTest.java
+// equalshashcode/IndividualTest.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.
@@ -13,12 +13,19 @@ public class IndividualTest {
         MapOfList.petPeople.values())
       for(Pet p : lp)
         pets.add(p);
-    System.out.println(pets);
+    pets.forEach(System.out::println);
   }
 }
 /* Output:
-[Cat Elsie May, Cat Pinkola, Cat Shackleton, Cat Stanford
+Cat Elsie May
-aka Stinky el Negro, Cymric Molly, Dog Margrett, Mutt Spot,
+Cat Pinkola
-Pug Louie aka Louis Snorkelstein Dupree, Rat Fizzy, Rat
+Cat Shackleton
-Freckly, Rat Fuzzy]
+Cat Stanford aka Stinky el Negro
+Cymric Molly
+Dog Margrett
+Mutt Spot
+Pug Louie aka Louis Snorkelstein Dupree
+Rat Fizzy
+Rat Freckly
+Rat Fuzzy
 */

equalshashcode/MapEntry.java

@@ -1,4 +1,4 @@
-// collectiontopics/MapEntry.java
+// equalshashcode/MapEntry.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.
@@ -24,21 +24,19 @@ public class MapEntry<K, V> implements Map.Entry<K, V> {
   }
   @Override
   public int hashCode() {
-    return (key==null ? 0 : key.hashCode()) ^
+    return Objects.hash(key, value);
-      (value==null ? 0 : value.hashCode());
   }
-  @Override
-  public boolean equals(Object o) {
-    if(!(o instanceof MapEntry)) return false;
   @SuppressWarnings("unchecked")
-    MapEntry<K, V> me = (MapEntry<K, V>)o;
+  @Override
-    return
+  public boolean equals(Object rval) {
-      (key == null ? me.getKey() == null :
+    return rval instanceof MapEntry &&
-        key.equals(me.getKey()))
+      Objects.equals(key,
-       &&
+        ((MapEntry<K, V>)rval).getKey()) &&
-      (value == null ? me.getValue() == null :
+      Objects.equals(value,
-        value.equals(me.getValue()));
+        ((MapEntry<K, V>)rval).getValue());
   }
   @Override
-  public String toString() { return key + "=" + value; }
+  public String toString() {
+    return key + "=" + value;
+  }
 }

equalshashcode/Prediction.java

@@ -0,0 +1,15 @@
+// equalshashcode/Prediction.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+// Predicting the weather
+import java.util.*;
+
+public class Prediction {
+  private static Random rand = new Random(47);
+  @Override
+  public String toString() {
+    return rand.nextBoolean() ?
+      "Six more weeks of Winter!" : "Early Spring!";
+  }
+}

equalshashcode/SimpleHashMap.java

@@ -1,4 +1,4 @@
-// collectiontopics/SimpleHashMap.java
+// equalshashcode/SimpleHashMap.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.
@@ -62,30 +62,29 @@ class SimpleHashMap<K, V> extends AbstractMap<K, V> {
   public static void main(String[] args) {
     SimpleHashMap<String,String> m =
       new SimpleHashMap<>();
-    m.putAll(Countries.capitals(25));
+    m.putAll(Countries.capitals(8));
-    System.out.println(m);
+    m.forEach((k, v) ->
-    System.out.println(m.get("ERITREA"));
+      System.out.println(k + "=" + v));
-    System.out.println(m.entrySet());
+    System.out.println(m.get("BENIN"));
+    m.entrySet().forEach(System.out::println);
   }
 }
 /* Output:
-{CAPE VERDE=Praia, ANGOLA=Luanda, ETHIOPIA=Addis Ababa,
+CAMEROON=Yaounde
-BENIN=Porto-Novo, CONGO=Brazzaville, LESOTHO=Maseru,
+ANGOLA=Luanda
-CENTRAL AFRICAN REPUBLIC=Bangui, EQUATORIAL GUINEA=Malabo,
+BURKINA FASO=Ouagadougou
-ERITREA=Asmara, COMOROS=Moroni, BURKINA FASO=Ouagadougou,
+BURUNDI=Bujumbura
-GABON=Libreville, THE GAMBIA=Banjul, GUINEA=Conakry,
+ALGERIA=Algiers
-EGYPT=Cairo, BURUNDI=Bujumbura, ALGERIA=Algiers,
+BENIN=Porto-Novo
-CAMEROON=Yaounde, GHANA=Accra, KENYA=Nairobi, COTE D'IVOIR
+CAPE VERDE=Praia
-(IVORY COAST)=Yamoussoukro, BISSAU=Bissau,
+BOTSWANA=Gaberone
-DJIBOUTI=Dijibouti, CHAD=N'djamena, BOTSWANA=Gaberone}
+Porto-Novo
-Asmara
+CAMEROON=Yaounde
-[CAPE VERDE=Praia, ANGOLA=Luanda, ETHIOPIA=Addis Ababa,
+ANGOLA=Luanda
-BENIN=Porto-Novo, CONGO=Brazzaville, LESOTHO=Maseru,
+BURKINA FASO=Ouagadougou
-CENTRAL AFRICAN REPUBLIC=Bangui, EQUATORIAL GUINEA=Malabo,
+BURUNDI=Bujumbura
-ERITREA=Asmara, COMOROS=Moroni, BURKINA FASO=Ouagadougou,
+ALGERIA=Algiers
-GABON=Libreville, THE GAMBIA=Banjul, GUINEA=Conakry,
+BENIN=Porto-Novo
-EGYPT=Cairo, BURUNDI=Bujumbura, ALGERIA=Algiers,
+CAPE VERDE=Praia
-CAMEROON=Yaounde, GHANA=Accra, KENYA=Nairobi, COTE D'IVOIR
+BOTSWANA=Gaberone
-(IVORY COAST)=Yamoussoukro, BISSAU=Bissau,
-DJIBOUTI=Dijibouti, CHAD=N'djamena, BOTSWANA=Gaberone]
 */

equalshashcode/SlowMap.java

@@ -1,4 +1,4 @@
-// collectiontopics/SlowMap.java
+// equalshashcode/SlowMap.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.
@@ -36,24 +36,29 @@ public class SlowMap<K, V> extends AbstractMap<K, V> {
   }
   public static void main(String[] args) {
     SlowMap<String,String> m= new SlowMap<>();
-    m.putAll(Countries.capitals(15));
+    m.putAll(Countries.capitals(8));
-    System.out.println(m);
+    m.forEach((k, v) ->
-    System.out.println(m.get("BULGARIA"));
+      System.out.println(k + "=" + v));
-    System.out.println(m.entrySet());
+    System.out.println(m.get("BENIN"));
+    m.entrySet().forEach(System.out::println);
   }
 }
 /* Output:
-{ANGOLA=Luanda, CAPE VERDE=Praia, EGYPT=Cairo,
+CAMEROON=Yaounde
-BURUNDI=Bujumbura, BENIN=Porto-Novo, ALGERIA=Algiers,
+ANGOLA=Luanda
-CAMEROON=Yaounde, CONGO=Brazzaville, CENTRAL AFRICAN
+BURKINA FASO=Ouagadougou
-REPUBLIC=Bangui, EQUATORIAL GUINEA=Malabo, COMOROS=Moroni,
+BURUNDI=Bujumbura
-DJIBOUTI=Dijibouti, BURKINA FASO=Ouagadougou,
+ALGERIA=Algiers
-CHAD=N'djamena, BOTSWANA=Gaberone}
+BENIN=Porto-Novo
-null
+CAPE VERDE=Praia
-[ANGOLA=Luanda, CAPE VERDE=Praia, EGYPT=Cairo,
+BOTSWANA=Gaberone
-BURUNDI=Bujumbura, BENIN=Porto-Novo, ALGERIA=Algiers,
+Porto-Novo
-CAMEROON=Yaounde, CONGO=Brazzaville, CENTRAL AFRICAN
+CAMEROON=Yaounde
-REPUBLIC=Bangui, EQUATORIAL GUINEA=Malabo, COMOROS=Moroni,
+ANGOLA=Luanda
-DJIBOUTI=Dijibouti, BURKINA FASO=Ouagadougou,
+BURKINA FASO=Ouagadougou
-CHAD=N'djamena, BOTSWANA=Gaberone]
+BURUNDI=Bujumbura
+ALGERIA=Algiers
+BENIN=Porto-Novo
+CAPE VERDE=Praia
+BOTSWANA=Gaberone
 */

equalshashcode/SpringDetector.java

@@ -0,0 +1,62 @@
+// equalshashcode/SpringDetector.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+// What will the weather be?
+import java.util.*;
+import java.util.stream.*;
+import java.util.function.*;
+import java.lang.reflect.*;
+
+public class SpringDetector {
+  public static <T extends Groundhog>
+  void detectSpring(Class<T> type) {
+    try {
+      Constructor<T> ghog =
+        type.getConstructor(int.class);
+      Map<Groundhog, Prediction> map =
+        IntStream.range(0, 10)
+        .mapToObj(i -> {
+          try {
+            return ghog.newInstance(i);
+          } catch(Exception e) {
+            throw new RuntimeException(e);
+          }
+        })
+        .collect(Collectors.toMap(
+          Function.identity(),
+          gh -> new Prediction()));
+      map.forEach((k, v) ->
+        System.out.println(k + ": " + v));
+      Groundhog gh = ghog.newInstance(3);
+      System.out.println(
+        "Looking up prediction for " + gh);
+      if(map.containsKey(gh))
+        System.out.println(map.get(gh));
+      else
+        System.out.println("Key not found: " + gh);
+    } catch(NoSuchMethodException |
+            IllegalAccessException |
+            InvocationTargetException |
+            InstantiationException e) {
+      throw new RuntimeException(e);
+    }
+  }
+  public static void main(String[] args) {
+    detectSpring(Groundhog.class);
+  }
+}
+/* Output:
+Groundhog #3: Six more weeks of Winter!
+Groundhog #0: Early Spring!
+Groundhog #8: Six more weeks of Winter!
+Groundhog #6: Early Spring!
+Groundhog #4: Early Spring!
+Groundhog #2: Six more weeks of Winter!
+Groundhog #1: Early Spring!
+Groundhog #9: Early Spring!
+Groundhog #5: Six more weeks of Winter!
+Groundhog #7: Six more weeks of Winter!
+Looking up prediction for Groundhog #3
+Key not found: Groundhog #3
+*/

equalshashcode/SpringDetector2.java

@@ -0,0 +1,25 @@
+// equalshashcode/SpringDetector2.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+// A working key
+
+public class SpringDetector2 {
+  public static void main(String[] args) {
+    SpringDetector.detectSpring(Groundhog2.class);
+  }
+}
+/* Output:
+Groundhog #0: Six more weeks of Winter!
+Groundhog #1: Early Spring!
+Groundhog #2: Six more weeks of Winter!
+Groundhog #3: Early Spring!
+Groundhog #4: Early Spring!
+Groundhog #5: Six more weeks of Winter!
+Groundhog #6: Early Spring!
+Groundhog #7: Early Spring!
+Groundhog #8: Six more weeks of Winter!
+Groundhog #9: Six more weeks of Winter!
+Looking up prediction for Groundhog #3
+Early Spring!
+*/

equalshashcode/StringHashCode.java

@@ -1,4 +1,4 @@
-// collectiontopics/StringHashCode.java
+// equalshashcode/StringHashCode.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.

equalshashcode/SubtypeEquality.java

@@ -0,0 +1,60 @@
+// equalshashcode/SubtypeEquality.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+import java.util.*;
+
+enum Size { SMALL, MEDIUM, LARGE }
+
+class Animal {
+  private static int counter = 0;
+  private final int id = counter++;
+  private final String name;
+  private final Size size;
+  public Animal(String name, Size size) {
+    this.name = name;
+    this.size = size;
+  }
+  @Override
+  public boolean equals(Object rval) {
+    return rval instanceof Animal &&
+      // Objects.equals(id, ((Animal)rval).id) && // [1]
+      Objects.equals(name, ((Animal)rval).name) &&
+      Objects.equals(size, ((Animal)rval).size);
+  }
+  @Override
+  public int hashCode() {
+    return Objects.hash(name, size);
+    // return Objects.hash(name, size, id);  // [2]
+  }
+  @Override
+  public String toString() {
+    return String.format("%s[%d]: %s %s %x",
+      getClass().getSimpleName(), id,
+      name, size, hashCode());
+  }
+}
+
+class Dog extends Animal {
+  public Dog(String name, Size size) {
+    super(name, size);
+  }
+}
+
+class Pig extends Animal {
+  public Pig(String name, Size size) {
+    super(name, size);
+  }
+}
+
+public class SubtypeEquality {
+  public static void main(String[] args) {
+    Set<Animal> pets = new HashSet<>();
+    pets.add(new Dog("Ralph", Size.MEDIUM));
+    pets.add(new Pig("Ralph", Size.MEDIUM));
+    pets.forEach(System.out::println);
+  }
+}
+/* Output:
+Dog[0]: Ralph MEDIUM a752aeee
+*/

equalshashcode/SubtypeEquality2.java

@@ -0,0 +1,40 @@
+// equalshashcode/SubtypeEquality2.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+import java.util.*;
+
+class Dog2 extends Animal {
+  public Dog2(String name, Size size) {
+    super(name, size);
+  }
+  @Override
+  public boolean equals(Object rval) {
+    return rval instanceof Dog2 &&
+      super.equals(rval);
+  }
+}
+
+class Pig2 extends Animal {
+  public Pig2(String name, Size size) {
+    super(name, size);
+  }
+  @Override
+  public boolean equals(Object rval) {
+    return rval instanceof Pig2 &&
+      super.equals(rval);
+  }
+}
+
+public class SubtypeEquality2 {
+  public static void main(String[] args) {
+    Set<Animal> pets = new HashSet<>();
+    pets.add(new Dog2("Ralph", Size.MEDIUM));
+    pets.add(new Pig2("Ralph", Size.MEDIUM));
+    pets.forEach(System.out::println);
+  }
+}
+/* Output:
+Dog2[0]: Ralph MEDIUM a752aeee
+Pig2[1]: Ralph MEDIUM a752aeee
+*/

equalshashcode/SuccinctEquality.java

@@ -1,4 +1,4 @@
-// collectiontopics/SuccinctEquality.java
+// equalshashcode/SuccinctEquality.java
 // (c)2017 MindView LLC: see Copyright.txt
 // We make no guarantees that this code is fit for any purpose.
 // Visit http://OnJava8.com for more book information.

generics/Holder.java

@@ -17,7 +17,7 @@ public class Holder<T> {
   }
   @Override
   public int hashCode() {
-    return Objects.hash(value);
+    return Objects.hashCode(value);
   }
   public static void main(String[] args) {
     Holder<Apple> apple = new Holder<>(new Apple());

gradle/subprojects.gradle

@@ -5,13 +5,16 @@ project(':validating') {
 }
 
 project(':collectiontopics') {
+    jmh {
+        include = 'collectiontopics.jmh.*'
+    }
+}
+
+project(':equalshashcode') {
     dependencies {
         compile project(':typeinfo')
         compile project(':collections')
     }
-    jmh {
-        include = 'collectiontopics.jmh.*'
-    }
 }
 
 project(':lowlevel') {

onjava/CountMap.java

@@ -44,7 +44,7 @@ extends AbstractMap<Integer,String> {
     }
     @Override
     public int hashCode() {
-      return Integer.valueOf(index).hashCode();
+      return Objects.hashCode(index);
     }
   }
   @Override
@@ -64,7 +64,7 @@ extends AbstractMap<Integer,String> {
       .limit(LIM)
       .forEach(System.out::println);
     System.out.println();
-    new Random().ints(LIM, 0, 1000)
+    new Random(47).ints(LIM, 0, 1000)
       .mapToObj(cm::get)
       .forEach(System.out::println);
   }
@@ -86,10 +86,10 @@ D0
 E0
 F0
 
-E4
+Y9
-X33
+J21
-P15
+R26
-L28
+D33
-M24
+Z36
-Y36
+N16
 */

onjava/Countries.java

@@ -225,7 +225,7 @@ public class Countries {
       }
       @Override
       public int hashCode() {
-        return DATA[index][0].hashCode();
+        return Objects.hashCode(DATA[index][0]);
       }
       @Override
       public String getKey() { return DATA[index][0]; }

typeinfo/pets/Individual.java

@@ -26,11 +26,7 @@ Individual implements Comparable<Individual> {
   }
   @Override
   public int hashCode() {
-    int result = 17;
+    return Objects.hash(name, id);
-    if(name != null)
-      result = 37 * result + name.hashCode();
-    result = 37 * result + (int)id;
-    return result;
   }
   @Override
   public int compareTo(Individual arg) {