Partial update to JDK 17 Features

Author: BruceEckel

collections/BasicRecord.java

@@ -0,0 +1,29 @@
+// collections/BasicRecord.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
+import java.util.*;
+
+record Employee(String name, int id) {}
+
+public class BasicRecord {
+  public static void main(String[] args) {
+    var bob = new Employee("Bob Dobbs", 11);
+    var dot = new Employee("Dorothy Gale", 9);
+    // bob.id = 12; // Error:
+    // id has private access in Employee
+    System.out.println(bob.name()); // Accessor
+    System.out.println(bob.id()); // Accessor
+    System.out.println(bob); // toString()
+    // Employee works as the key in a Map:
+    var map = Map.of(bob, "A", dot, "B");
+    System.out.println(map);
+  }
+}
+/* Output:
+Bob Dobbs
+11
+Employee[name=Bob Dobbs, id=11]
+{Employee[name=Dorothy Gale, id=9]=B, Employee[name=Bob Dobbs, id=11]=A}
+*/

collections/CompactConstructor.java

@@ -0,0 +1,16 @@
+// collections/CompactConstructor.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
+
+record Point(int x, int y) {
+  void assertPositive(int val) {
+    if(val < 0)
+      throw new IllegalArgumentException("negative");
+  }
+  Point { // Compact: No parameter list
+    assertPositive(x);
+    assertPositive(y);
+  }
+}

collections/ComposedRecord.java

@@ -0,0 +1,10 @@
+// collections/ComposedRecord.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
+
+record Company(Employee[] e) {}
+
+// class Conglomerate extends Company {}
+// error: cannot inherit from final Company

collections/CopyRecord.java

@@ -0,0 +1,18 @@
+// collections/CopyRecord.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
+
+record R(int a, double b, char c) {}
+
+public class CopyRecord {
+  public static void main(String[] args) {
+    var r1 = new R(11, 2.2, 'z');
+    var r2 = new R(r1.a(), r1.b(), r1.c());
+    System.out.println(r1.equals(r2));
+  }
+}
+/* Output:
+true
+*/

collections/FinalFields.java

@@ -0,0 +1,12 @@
+// collections/FinalFields.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
+import java.util.*;
+
+record FinalFields(int i) {
+  int timesTen() { return i * 10; }
+  // void tryToChange() { i++; } // Error:
+  // cannot assign a value to final variable i
+}

collections/GenericTypeInference.java

@@ -0,0 +1,20 @@
+// collections/GenericTypeInference.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 11
+import java.util.*;
+
+public class GenericTypeInference {
+  void old() {
+    ArrayList<Apple> apples = new ArrayList<>();
+  }
+  void modern() {
+    var apples = new ArrayList<Apple>();
+  }
+  void pitFall() {
+    var apples = new ArrayList<>();
+    apples.add(new Apple());
+    apples.get(0); // Comes back as plain Object
+  }
+}

collections/ImplementingRecord.java

@@ -0,0 +1,14 @@
+// collections/ImplementingRecord.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
+
+interface Star {
+  double brightness();
+  double density();
+}
+
+record RedDwarf(double brightness) implements Star {
+  @Override public double density() { return 100.0; }
+}

collections/NestedLocalRecords.java

@@ -0,0 +1,12 @@
+// collections/NestedLocalRecords.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 NestedLocalRecords {
+  record Nested(String s) {}
+  void method() {
+    record Local(String s) {}
+  }
+}

collections/NormalConstructor.java

@@ -0,0 +1,11 @@
+// collections/NormalConstructor.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
+
+record Value(int x) {
+  Value(int x) { // With the parameter list
+    this.x = x; // Must explicitly initialize
+  }
+}

collections/PlusTen.java

@@ -0,0 +1,20 @@
+// collections/PlusTen.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
+
+record PlusTen(int x) {
+  PlusTen {
+    x += 10;
+  }
+  // Adjustment to field can only happen in
+  // the constructor. Still not legal:
+  // void mutate() { x += 10; }
+  public static void main(String[] args) {
+    System.out.println(new PlusTen(10));
+  }
+}
+/* Output:
+PlusTen[x=20]
+*/