New Feature Examples, Corrections & Rewrites

README.md

@@ -8,6 +8,7 @@ includes tests to verify that the code in the book is correct.
 
 > NOTE: Do not attempt to use JDK 16 or greater with gradle. 
 > This produces a `BUG!` message from Gradle, which is broken for those versions.
+> To test new Java features in JDK 16 or 17 you must compile and run those examples by hand.
 
 ## Contents
 

collectiontopics/CanonicalMapping.java

@@ -4,49 +4,29 @@
 // Visit http://OnJava8.com for more book information.
 // Demonstrates WeakHashMap
 import java.util.*;
-
-class Element {
-  private String ident;
-  Element(String id) { ident = id; }
-  @Override public String toString() { return ident; }
-  @Override public int hashCode() {
-    return Objects.hashCode(ident);
-  }
-  @Override public boolean equals(Object r) {
-    return r instanceof Element &&
-      Objects.equals(ident, ((Element)r).ident);
-  }
-  @SuppressWarnings("deprecation")
-  @Override protected void finalize() {
-    System.out.println("Finalizing " +
-      getClass().getSimpleName() + " " + ident);
-  }
-}
-
-class Key extends Element {
-  Key(String id) { super(id); }
-}
-
-class Value extends Element {
-  Value(String id) { super(id); }
-}
+import java.util.stream.*;
 
 public class CanonicalMapping {
+  static void showKeys(Map<String, String> m) {
+    // Display sorted keys
+    List<String> keys = new ArrayList<>(m.keySet());
+    Collections.sort(keys);
+    System.out.println(keys);
+  }
   public static void main(String[] args) {
-    int size = 1000;
-    // Or, choose size via the command line:
-    if(args.length > 0)
-      size = Integer.valueOf(args[0]);
-    Key[] keys = new Key[size];
-    WeakHashMap<Key,Value> map =
+    int size = 100;
+    String[] savedKeys = new String[size];
+    WeakHashMap<String,String> map =
       new WeakHashMap<>();
     for(int i = 0; i < size; i++) {
-      Key k = new Key(Integer.toString(i));
-      Value v = new Value(Integer.toString(i));
+      String key = String.format("%03d", i);
+      String value = Integer.toString(i);
       if(i % 3 == 0)
-        keys[i] = k; // Save as "real" references
-      map.put(k, v);
+        savedKeys[i] = key; // Save as "real" references
+      map.put(key, value);
     }
+    showKeys(map);
     System.gc();
+    showKeys(map);
   }
 }

collectiontopics/ListSortSearch.java

@@ -13,9 +13,9 @@ public class ListSortSearch {
     System.out.println(list);
     Collections.shuffle(list, new Random(47));
     System.out.println("Shuffled: " + list);
-    // Use ListIterator to trim off last elements:
-    ListIterator<String> it = list.listIterator(10);
-    while(it.hasNext()) {
+    ListIterator<String> it =
+      list.listIterator(10);               // [1]
+    while(it.hasNext()) {                  // [2]
       it.next();
       it.remove();
     }

collectiontopics/QueueBehavior.java

@@ -15,7 +15,7 @@ public class QueueBehavior {
   }
   static void test(int id, Queue<String> queue) {
     System.out.print(id + ": ");
-    strings().map(queue::offer).count();
+    strings().forEach(queue::offer);
     while(queue.peek() != null)
       System.out.print(queue.remove() + " ");
     System.out.println();

concurrent/PSP2.txt

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-1: ForkJoinPool.commonPool-worker-2
+1: main
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enumerations/ArrowInSwitch.java

@@ -0,0 +1,42 @@
+// enumerations/ArrowInSwitch.java
+// (c)2021 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.
+// {NewFeature} Since JDK 14
+import static java.util.stream.IntStream.range;
+
+public class ArrowInSwitch {
+  static void colons(int i) {
+    switch(i) {
+      case 1: System.out.println("one");
+              break;
+      case 2: System.out.println("two");
+              break;
+      case 3: System.out.println("three");
+              break;
+      default: System.out.println("default");
+    }
+  }
+  static void arrows(int i) {
+    switch(i) {
+      case 1 -> System.out.println("one");
+      case 2 -> System.out.println("two");
+      case 3 -> System.out.println("three");
+      default -> System.out.println("default");
+    }
+  }
+  public static void main(String[] args) {
+    range(0, 4).forEach(i -> colons(i));
+    range(0, 4).forEach(i -> arrows(i));
+  }
+}
+/* Output:
+default
+one
+two
+three
+default
+one
+two
+three
+*/

enumerations/CaseNull.java

@@ -0,0 +1,92 @@
+// enumerations/CaseNull.java
+// (c)2021 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.
+// {NewFeature} Preview in JDK 17
+// Compile with javac flags:
+//   --enable-preview --source 17
+// Run with java flag: --enable-preview
+import java.util.*;
+import java.util.function.*;
+
+public class CaseNull {
+  static void old(String s) {
+    if(s == null) {
+      System.out.println("null");
+      return;
+    }
+    switch(s) {
+      case "XX" -> System.out.println("XX");
+      default   -> System.out.println("default");
+    }
+  }
+  static void checkNull(String s) {
+    switch(s) {
+      case "XX" -> System.out.println("XX");
+      case null -> System.out.println("null");
+      default   -> System.out.println("default");
+    }
+    // Works with colon syntax, too:
+    switch(s) {
+      case "XX": System.out.println("XX");
+                 break;
+      case null: System.out.println("null");
+                 break;
+      default  : System.out.println("default");
+    }
+  }
+  static void defaultOnly(String s) {
+    switch(s) {
+      case "XX" -> System.out.println("XX");
+      default   -> System.out.println("default");
+    }
+  }
+  static void combineNullAndCase(String s) {
+    switch(s) {
+      case "XX", null -> System.out.println("XX|null");
+      default -> System.out.println("default");
+    }
+  }
+  static void combineNullAndDefault(String s) {
+    switch(s) {
+      case "XX" -> System.out.println("XX");
+      case null, default -> System.out.println("both");
+    }
+  }
+  static void test(Consumer<String> cs) {
+    cs.accept("XX");
+    cs.accept("YY");
+    try {
+      cs.accept(null);
+    } catch(NullPointerException e) {
+      System.out.println(e.getMessage());
+    }
+  }
+  public static void main(String[] args) {
+    test(CaseNull::old);
+    test(CaseNull::checkNull);
+    test(CaseNull::defaultOnly);
+    test(CaseNull::combineNullAndCase);
+    test(CaseNull::combineNullAndDefault);
+  }
+}
+/* Output:
+XX
+default
+null
+XX
+XX
+default
+default
+null
+null
+XX
+default
+Cannot invoke "String.hashCode()" because "<local1>" is null
+XX|null
+default
+XX|null
+XX
+both
+both
+*/

enumerations/Dominance.java

@@ -0,0 +1,20 @@
+// enumerations/Dominance.java
+// (c)2021 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.
+// {NewFeature} Preview in JDK 17
+// Compile with javac flags:
+//   --enable-preview --source 17
+import java.util.*;
+
+sealed interface Base {}
+record Derived() implements Base {}
+
+public class Dominance {
+  static String test(Base base) {
+    return switch(base) {
+      case Derived d -> "Derived";
+      case Base b -> "B";            // [1]
+    };
+  }
+}

enumerations/EnumSwitch.java

@@ -0,0 +1,17 @@
+// enumerations/EnumSwitch.java
+// (c)2021 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.
+// {NewFeature} Since JDK 14
+
+public class EnumSwitch {
+  enum Signal { GREEN, YELLOW, RED, }
+  Signal color = Signal.RED;
+  public void change() {
+    color = switch(color) {
+      case RED -> Signal.GREEN;
+      case GREEN -> Signal.YELLOW;
+      case YELLOW -> Signal.RED;
+    };
+  }
+}

enumerations/NormalLiskov.java

@@ -0,0 +1,40 @@
+// enumerations/NormalLiskov.java
+// (c)2021 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.stream.*;
+
+interface LifeForm {
+  String move();
+  String react();
+}
+
+class Worm implements LifeForm {
+  @Override public String move() {
+    return "Worm::move()";
+  }
+  @Override public String react() {
+    return "Worm::react()";
+  }
+}
+
+class Giraffe implements LifeForm {
+  @Override public String move() {
+    return "Giraffe::move()";
+  }
+  @Override public String react() {
+    return "Giraffe::react()";
+  }
+}
+
+public class NormalLiskov {
+  public static void main(String[] args) {
+    Stream.of(new Worm(), new Giraffe())
+      .forEach(lf -> System.out.println(
+        lf.move() + " " + lf.react()));
+  }
+}
+/* Output:
+Worm::move() Worm::react()
+Giraffe::move() Giraffe::react()
+*/

enumerations/ObjectMatch.java

@@ -0,0 +1,46 @@
+// enumerations/ObjectMatch.java
+// (c)2021 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.
+// {NewFeature} Preview in JDK 17
+// Compile with javac flags:
+//   --enable-preview --source 17
+// Run with java flag: --enable-preview
+import java.util.*;
+
+record XX() {}
+
+public class ObjectMatch {
+  static String match(Object o) {
+    return switch(o) {
+      case Dog d -> "Walk the dog";
+      case Fish f -> "Change the fish water";
+      case Pet sp -> "Not dog or fish";
+      case String s -> "String " + s;
+      case Integer i -> "Integer " + i;
+      case String[] sa -> String.join(", ", sa);
+      case null, XX xx -> "null or XX: " + xx;
+      default -> "Something else";
+    };
+  }
+  public static void main(String[] args) {
+    List.of(new Dog(), new Fish(), new Pet(),
+      "Oscar", Integer.valueOf(12),
+      Double.valueOf("47.74"),
+      new String[]{ "to", "the", "point" },
+      new XX()
+    ).forEach(
+      p -> System.out.println(match(p))
+    );
+  }
+}
+/* Output:
+Walk the dog
+Change the fish water
+Not dog or fish
+String Oscar
+Integer 12
+Something else
+to, the, point
+null or Object: XX[]
+*/

enumerations/OddScoping.java

@@ -0,0 +1,27 @@
+// enumerations/OddScoping.java
+// (c)2021 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.
+// {NewFeature} Since JDK 16
+
+public class OddScoping {
+  static void f(Object o) {
+    if(!(o instanceof String s)) {
+      System.out.println("Not a String");
+      throw new RuntimeException();
+    }
+    // s is in scope here!
+    System.out.println(s.toUpperCase());  // [1]
+  }
+  public static void main(String[] args) {
+    f("Curiouser and Curiouser");
+    f(null);
+  }
+}
+/* Output:
+CURIOUSER AND CURIOUSER
+Not a String
+Exception in thread "main" java.lang.RuntimeException
+        at OddScoping.f(OddScoping.java:8)
+        at OddScoping.main(OddScoping.java:15)
+*/

enumerations/People.java

@@ -0,0 +1,46 @@
+// enumerations/People.java
+// (c)2021 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.
+// {NewFeature} Preview in JDK 17
+// Compile with javac flags:
+//   --enable-preview --source 17
+// Run with java flag: --enable-preview
+import java.util.*;
+
+record Person(String name, int age) {}
+
+public class People {
+  static String categorize(Person person) {
+    return switch(person) {
+      case Person p && p.age() > 40          // [1]
+        -> p + " is middle aged";
+      case Person p &&
+        (p.name().contains("D") || p.age() == 14)
+        -> p + " D or 14";
+      case Person p && !(p.age() >= 100)     // [2]
+        -> p + " is not a centenarian";
+      case Person p -> p + " Everyone else";
+    };
+  }
+  public static void main(String[] args) {
+    List.of(
+      new Person("Dorothy", 15),
+      new Person("John Bigboote", 42),
+      new Person("Morty", 14),
+      new Person("Morty Jr.", 1),
+      new Person("Jose", 39),
+      new Person("Kane", 118)
+    ).forEach(
+      p -> System.out.println(categorize(p))
+    );
+  }
+}
+/* Output:
+Person[name=Dorothy, age=15] D or 14
+Person[name=John Bigboote, age=42] is middle aged
+Person[name=Morty, age=14] D or 14
+Person[name=Morty Jr., age=1] is not a centenarian
+Person[name=Jose, age=39] is not a centenarian
+Person[name=Kane, age=118] is middle aged
+*/

enumerations/Pet.java

@@ -0,0 +1,16 @@
+// enumerations/Pet.java
+// (c)2021 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.
+
+public class Pet {
+  void feed() {}
+}
+
+class Dog extends Pet {
+  void walk() {}
+}
+
+class Fish extends Pet {
+  void changeWater() {}
+}

enumerations/PetPatternMatch.java

@@ -0,0 +1,22 @@
+// enumerations/PetPatternMatch.java
+// (c)2021 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.
+// {NewFeature} Preview in JDK 17
+// Compile with javac flags:
+//   --enable-preview --source 17
+import java.util.*;
+
+public class PetPatternMatch {
+  static void careFor(Pet p) {
+    switch(p) {
+      case Dog d -> d.walk();
+      case Fish f -> f.changeWater();
+      case Pet sp -> sp.feed();
+    };
+  }
+  static void petCare() {
+    List.of(new Dog(), new Fish())
+      .forEach(p -> careFor(p));
+  }
+}

enumerations/PetPatternMatch2.java

@@ -0,0 +1,36 @@
+// enumerations/PetPatternMatch2.java
+// (c)2021 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.
+// {NewFeature} Preview in JDK 17
+// Compile with javac flags:
+//   --enable-preview --source 17
+package sealedpet;
+import java.util.*;
+
+sealed interface Pet {
+  void feed();
+}
+
+final class Dog implements Pet {
+  @Override public void feed() {}
+  void walk() {}
+}
+
+final class Fish implements Pet {
+  @Override public void feed() {}
+  void changeWater() {}
+}
+
+public class PetPatternMatch2 {
+  static void careFor(Pet p) {
+    switch(p) {
+      case Dog d -> d.walk();
+      case Fish f -> f.changeWater();
+    };
+  }
+  static void petCare() {
+    List.of(new Dog(), new Fish())
+      .forEach(p -> careFor(p));
+  }
+}

enumerations/Planets.java

@@ -0,0 +1,36 @@
+// enumerations/Planets.java
+// (c)2021 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.
+// {NewFeature} Since JDK 14
+
+enum CelestialBody {
+  MERCURY, VENUS, EARTH, MARS, JUPITER,
+  SATURN, URANUS, NEPTUNE, PLUTO
+}
+
+public class Planets {
+  public static String classify(CelestialBody b) {
+    var result = switch(b) {
+      case  MERCURY, VENUS, EARTH,
+            MARS, JUPITER,
+            SATURN, URANUS, NEPTUNE -> {
+              System.out.print("A planet: ");
+              yield b.toString();
+            }
+      case  PLUTO -> {
+              System.out.print("Not a planet: ");
+              yield b.toString();
+            }
+    };
+    return result;
+  }
+  public static void main(String[] args) {
+    System.out.println(classify(CelestialBody.MARS));
+    System.out.println(classify(CelestialBody.PLUTO));
+  }
+}
+/* Output:
+A planet: MARS
+Not a planet: PLUTO
+*/

enumerations/SealedPatternMatch.java

@@ -0,0 +1,48 @@
+// enumerations/SealedPatternMatch.java
+// (c)2021 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.
+// {NewFeature} Preview in JDK 17
+// Compile with javac flags:
+//   --enable-preview --source 17
+// Run with java flag: --enable-preview
+import java.util.*;
+
+sealed interface Transport {};
+record Bicycle(String id) implements Transport {};
+record Glider(int size) implements Transport {};
+record Surfboard(double weight) implements Transport {};
+// If you uncomment this:
+// record Skis(int length) implements Transport {};
+// You get an error: "the switch expression
+// does not cover all possible input values"
+
+public class SealedPatternMatch {
+  static String exhaustive(Transport t) {
+    return switch(t) {
+      case Bicycle b -> "Bicycle " + b.id();
+      case Glider g -> "Glider " + g.size();
+      case Surfboard s -> "Surfboard " + s.weight();
+    };
+  }
+  public static void main(String[] args) {
+    List.of(
+      new Bicycle("Bob"),
+      new Glider(65),
+      new Surfboard(6.4)
+    ).forEach(
+      t -> System.out.println(exhaustive(t))
+    );
+    try {
+      exhaustive(null); // Always possible!  // [1]
+    } catch(NullPointerException e) {
+      System.out.println("Not exhaustive: " + e);
+    }
+  }
+}
+/* Output:
+Bicycle Bob
+Glider 65
+Surfboard 6.4
+Not exhaustive: java.lang.NullPointerException
+*/

enumerations/Shapes.java

@@ -0,0 +1,53 @@
+// enumerations/Shapes.java
+// (c)2021 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.
+// {NewFeature} Preview in JDK 17
+// Compile with javac flags:
+//   --enable-preview --source 17
+// Run with java flag: --enable-preview
+import java.util.*;
+
+sealed interface Shape {
+  double area();
+}
+
+record Circle(double radius) implements Shape {
+  @Override public double area() {
+    return Math.PI * radius * radius;
+  }
+}
+
+record Rectangle(double side1, double side2)
+  implements Shape {
+  @Override public double area() {
+    return side1 * side2;
+  }
+}
+
+public class Shapes {
+  static void classify(Shape s) {
+    System.out.println(switch(s) {
+      case Circle c && c.area() < 100.0
+        -> "Small Circle: " + c;
+      case Circle c -> "Large Circle: " + c;
+      case Rectangle r && r.side1() == r.side2()
+        -> "Square: " + r;
+      case Rectangle r -> "Rectangle: " + r;
+    });
+  }
+  public static void main(String[] args) {
+    List.of(
+      new Circle(5.0),
+      new Circle(25.0),
+      new Rectangle(12.0, 12.0),
+      new Rectangle(12.0, 15.0)
+    ).forEach(t -> classify(t));
+  }
+}
+/* Output:
+Small Circle: Circle[radius=5.0]
+Large Circle: Circle[radius=25.0]
+Square: Rectangle[side1=12.0, side2=12.0]
+Rectangle: Rectangle[side1=12.0, side2=15.0]
+*/

enumerations/SmartCasting.java

@@ -0,0 +1,36 @@
+// enumerations/SmartCasting.java
+// (c)2021 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.
+// {NewFeature} Since JDK 16
+
+public class SmartCasting {
+  static void dumb(Object x) {
+    if(x instanceof String) {
+      String s = (String)x;
+      if(s.length() > 0) {
+        System.out.format(
+          "%d %s%n", s.length(), s.toUpperCase());
+      }
+    }
+  }
+  static void smart(Object x) {
+    if(x instanceof String s && s.length() > 0) {
+      System.out.format(
+        "%d %s%n", s.length(), s.toUpperCase());
+    }
+  }
+  static void wrong(Object x) {
+    // "Or" never works:
+    // if(x instanceof String s || s.length() > 0) {}
+    // error: cannot find symbol   ^
+  }
+  public static void main(String[] args) {
+    dumb("dumb");
+    smart("smart");
+  }
+}
+/* Output:
+4 DUMB
+5 SMART
+*/

enumerations/SwitchExpression.java

@@ -0,0 +1,38 @@
+// enumerations/SwitchExpression.java
+// (c)2021 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.
+// {NewFeature} Since JDK 14
+import java.util.*;
+
+public class SwitchExpression {
+  static int colon(String s) {
+    var result = switch(s) {
+      case "i": yield 1;
+      case "j": yield 2;
+      case "k": yield 3;
+      default:  yield 0;
+    };
+    return result;
+  }
+  static int arrow(String s) {
+    var result = switch(s) {
+      case "i" -> 1;
+      case "j" -> 2;
+      case "k" -> 3;
+      default  -> 0;
+    };
+    return result;
+  }
+  public static void main(String[] args) {
+    for(var s: new String[]{"i", "j", "k", "z"})
+      System.out.format(
+        "%s %d %d%n", s, colon(s), arrow(s));
+  }
+}
+/* Output:
+i 1 1
+j 2 2
+k 3 3
+z 0 0
+*/

enumerations/Tanks.java

@@ -0,0 +1,47 @@
+// enumerations/Tanks.java
+// (c)2021 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.
+// {NewFeature} Preview in JDK 17
+// Compile with javac flags:
+//   --enable-preview --source 17
+// Run with java flag: --enable-preview
+import java.util.*;
+
+enum Type { TOXIC, FLAMMABLE, NEUTRAL }
+
+record Level(int percent) {
+  Level {
+    if(percent < 0 || percent > 100)
+      throw new IndexOutOfBoundsException(
+        percent + " percent");
+  }
+}
+
+record Tank(Type type, Level level) {}
+
+public class Tanks {
+  static String check(Tank tank) {
+    return switch(tank) {
+      case Tank t && t.type() == Type.TOXIC
+        -> "Toxic: " + t;
+      case Tank t && (                 // [1]
+          t.type() == Type.TOXIC &&
+          t.level().percent() < 50
+        ) -> "Toxic, low: " + t;
+      case Tank t && t.type() == Type.FLAMMABLE
+        -> "Flammable: " + t;
+      // Equivalent to "default":
+      case Tank t -> "Other Tank: " + t;
+    };
+  }
+  public static void main(String[] args) {
+    List.of(
+      new Tank(Type.TOXIC, new Level(49)),
+      new Tank(Type.FLAMMABLE, new Level(52)),
+      new Tank(Type.NEUTRAL, new Level(75))
+    ).forEach(
+      t -> System.out.println(check(t))
+    );
+  }
+}

housekeeping/ForTypeInference.java

@@ -10,7 +10,7 @@ public class ForTypeInference {
       System.out.println(s);
   }
 }
-/* Ouput:
+/* Output:
 NOT
 MILD
 MEDIUM

serialization/AStoreCADState.java

@@ -11,49 +11,37 @@ enum Color { RED, BLUE, GREEN }
 
 abstract class Shape implements Serializable {
   private int xPos, yPos, dimension;
-  private static Random rand = new Random(47);
-  private static int counter = 0;
-  public abstract void setColor(Color newColor);
-  public abstract Color getColor();
   Shape(int xVal, int yVal, int dim) {
     xPos = xVal;
     yPos = yVal;
     dimension = dim;
   }
+  public abstract void setColor(Color newColor);
+  public abstract Color getColor();
   @Override public String toString() {
-    return getClass() + "Color[" + getColor() +
-      "] xPos[" + xPos + "] yPos[" + yPos +
-      "] dim[" + dimension + "]\n";
+    return "\n" + getClass() + " " + getColor() +
+      " xPos[" + xPos + "] yPos[" + yPos +
+      "] dim[" + dimension + "]";
   }
+  private static Random rand = new Random(47);
+  private static int counter = 0;
   public static Shape randomFactory() {
     int xVal = rand.nextInt(100);
     int yVal = rand.nextInt(100);
     int dim = rand.nextInt(100);
-    switch(counter++ % 3) {
+    switch(counter++ % 2) {
       default:
       case 0: return new Circle(xVal, yVal, dim);
-      case 1: return new Square(xVal, yVal, dim);
-      case 2: return new Line(xVal, yVal, dim);
+      case 1: return new Line(xVal, yVal, dim);
     }
   }
 }
 
 class Circle extends Shape {
-  private static Color color = Color.RED;
   Circle(int xVal, int yVal, int dim) {
     super(xVal, yVal, dim);
   }
-  @Override public void setColor(Color newColor) {
-    color = newColor;
-  }
-  @Override public Color getColor() { return color; }
-}
-
-class Square extends Shape {
   private static Color color = Color.RED;
-  Square(int xVal, int yVal, int dim) {
-    super(xVal, yVal, dim);
-  }
   @Override public void setColor(Color newColor) {
     color = newColor;
   }
@@ -61,35 +49,36 @@ class Square extends Shape {
 }
 
 class Line extends Shape {
+  Line(int xVal, int yVal, int dim) {
+    super(xVal, yVal, dim);
+  }
   private static Color color = Color.RED;
+  @Override public void setColor(Color newColor) {
+    color = newColor;
+  }
+  @Override public Color getColor() { return color; }
   public static void
   serializeStaticState(ObjectOutputStream os)
-  throws IOException { os.writeObject(color); }
+  throws IOException {
+    os.writeObject(color);
+  }
   public static void
   deserializeStaticState(ObjectInputStream os)
   throws IOException, ClassNotFoundException {
     color = (Color)os.readObject();
   }
-  Line(int xVal, int yVal, int dim) {
-    super(xVal, yVal, dim);
-  }
-  @Override public void setColor(Color newColor) {
-    color = newColor;
-  }
-  @Override public Color getColor() { return color; }
 }
 
 public class AStoreCADState {
   public static void main(String[] args) {
     List<Class<? extends Shape>> shapeTypes =
-      Arrays.asList(
-        Circle.class, Square.class, Line.class);
-    List<Shape> shapes = IntStream.range(0, 10)
+      Arrays.asList(Circle.class, Line.class);
+    List<Shape> shapes = IntStream.range(0, 5)
       .mapToObj(i -> Shape.randomFactory())
       .collect(Collectors.toList());
     // Set all the static colors to GREEN:
     shapes.forEach(s -> s.setColor(Color.GREEN));
-    // Save the state vector:
+    // Serialize everything to CADState.dat:
     try(
       ObjectOutputStream out =
         new ObjectOutputStream(
@@ -106,15 +95,10 @@ public class AStoreCADState {
   }
 }
 /* Output:
-[class CircleColor[GREEN] xPos[58] yPos[55] dim[93]
-, class SquareColor[GREEN] xPos[61] yPos[61] dim[29]
-, class LineColor[GREEN] xPos[68] yPos[0] dim[22]
-, class CircleColor[GREEN] xPos[7] yPos[88] dim[28]
-, class SquareColor[GREEN] xPos[51] yPos[89] dim[9]
-, class LineColor[GREEN] xPos[78] yPos[98] dim[61]
-, class CircleColor[GREEN] xPos[20] yPos[58] dim[16]
-, class SquareColor[GREEN] xPos[40] yPos[11] dim[22]
-, class LineColor[GREEN] xPos[4] yPos[83] dim[6]
-, class CircleColor[GREEN] xPos[75] yPos[10] dim[42]
-]
+[
+class Circle GREEN xPos[58] yPos[55] dim[93],
+class Line GREEN xPos[61] yPos[61] dim[29],
+class Circle GREEN xPos[68] yPos[0] dim[22],
+class Line GREEN xPos[7] yPos[88] dim[28],
+class Circle GREEN xPos[51] yPos[89] dim[9]]
 */

serialization/RecoverCADState.java

@@ -19,8 +19,7 @@ public class RecoverCADState {
       List<Class<? extends Shape>> shapeTypes =
         (List<Class<? extends Shape>>)in.readObject();
       Line.deserializeStaticState(in);
-      List<Shape> shapes =
-        (List<Shape>)in.readObject();
+      List<Shape> shapes = (List<Shape>)in.readObject();
       System.out.println(shapes);
     } catch(IOException | ClassNotFoundException e) {
       throw new RuntimeException(e);
@@ -28,15 +27,10 @@ public class RecoverCADState {
   }
 }
 /* Output:
-[class CircleColor[RED] xPos[58] yPos[55] dim[93]
-, class SquareColor[RED] xPos[61] yPos[61] dim[29]
-, class LineColor[GREEN] xPos[68] yPos[0] dim[22]
-, class CircleColor[RED] xPos[7] yPos[88] dim[28]
-, class SquareColor[RED] xPos[51] yPos[89] dim[9]
-, class LineColor[GREEN] xPos[78] yPos[98] dim[61]
-, class CircleColor[RED] xPos[20] yPos[58] dim[16]
-, class SquareColor[RED] xPos[40] yPos[11] dim[22]
-, class LineColor[GREEN] xPos[4] yPos[83] dim[6]
-, class CircleColor[RED] xPos[75] yPos[10] dim[42]
-]
+[
+class Circle RED xPos[58] yPos[55] dim[93],
+class Line GREEN xPos[61] yPos[61] dim[29],
+class Circle RED xPos[68] yPos[0] dim[22],
+class Line GREEN xPos[7] yPos[88] dim[28],
+class Circle RED xPos[51] yPos[89] dim[9]]
 */

streams/StreamOfRandoms.java

@@ -15,6 +15,5 @@ public class StreamOfRandoms {
   }
 }
 /* Output:
-58 -1 55 93 -1 61 61 29 -1 68 0 22 7 -1 88 28 51 89 9
--1
+58 -1 55 93 -1 61 61 29 -1 68 0 22 7 -1 88 28 51 89 9 -1
 */

strings/BackSlashes.java

@@ -0,0 +1,26 @@
+// strings/BackSlashes.java
+// (c)2021 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.
+
+public class BackSlashes {
+  public static void main(String[] args) {
+    String one = "\\";
+    String two = "\\\\";
+    String three = "\\\\\\";
+    System.out.println(one);
+    System.out.println(two);
+    System.out.println(three);
+    System.out.println(one.matches("\\\\"));
+    System.out.println(two.matches("\\\\\\\\"));
+    System.out.println(three.matches("\\\\\\\\\\\\"));
+  }
+}
+/* Output:
+\
+\\
+\\\
+true
+true
+true
+*/

strings/IntegerMatch.java

@@ -2,13 +2,17 @@
 // (c)2021 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.stream.*;
 
 public class IntegerMatch {
   public static void main(String[] args) {
-    System.out.println("-1234".matches("-?\\d+"));
-    System.out.println("5678".matches("-?\\d+"));
-    System.out.println("+911".matches("-?\\d+"));
-    System.out.println("+911".matches("(-|\\+)?\\d+"));
+    String possiblyMinus = "-?\\d+";
+    Stream.of(
+      "-1234".matches(possiblyMinus),
+      "5678".matches(possiblyMinus),
+      "+911".matches(possiblyMinus),
+      "+911".matches("(-|\\+)?\\d+")
+    ).forEach(System.out::println);
   }
 }
 /* Output:

strings/JGrep.java

@@ -4,7 +4,7 @@
 // Visit http://OnJava8.com for more book information.
 // A very simple version of the "grep" program
 // {java JGrep
-// WhitherStringBuilder.java 'return|for|String'}
+// WhitherStringBuilder.java "return|for|String"}
 import java.util.regex.*;
 import java.nio.file.*;
 import java.util.stream.*;
@@ -18,19 +18,33 @@ public class JGrep {
       System.exit(0);
     }
     Pattern p = Pattern.compile(args[1]);
-    // Iterate through the lines of the input file:
-    int index = 0;
     Matcher m = p.matcher("");
-    for(String line :
-        Files.readAllLines(Paths.get(args[0]))) {
+    // Iterate through the lines of the input file:
+    Files.readAllLines(Paths.get(args[0])).forEach(
+      line -> {
         m.reset(line);
         while(m.find())
-        System.out.println(index++ + ": " +
+          System.out.println(
             m.group() + ": " + m.start());
       }
+    );
   }
 }
 /* Output:
-0: for: 4
-1: for: 4
+String: 18
+String: 20
+String: 9
+String: 25
+String: 4
+for: 4
+String: 8
+return: 4
+String: 9
+String: 25
+String: 4
+String: 31
+for: 4
+String: 8
+return: 4
+String: 20
 */

validating/SimpleDebugging.java

@@ -23,18 +23,3 @@ public class SimpleDebugging {
     foo1();
   }
 }
-/* Output:
-In foo1
-In foo2
-In foo3
-___[ Error Output ]___
-Exception in thread "main"
-java.lang.ArithmeticException: / by zero
-        at
-SimpleDebugging.foo3(SimpleDebugging.java:17)
-        at
-SimpleDebugging.foo2(SimpleDebugging.java:11)
-        at SimpleDebugging.foo1(SimpleDebugging.java:7)
-        at
-SimpleDebugging.main(SimpleDebugging.java:20)
-*/