add an example of record equals/hashCode/toString

Author: forax

chapter12-equals_hashCode_toString.jsh

@@ -125,4 +125,14 @@ System.out.println(user1);
 
 // For a record, the methods `equals()`/`hashCode()` and `toString()` are already provided
 // so usually you don't have to provide a new implementation.
-
+record User(String name, int age) {
+  public User {
+    Objects.requireNonNull(name);
+  }
+  // the compiler automatically adds equals/hashCode/toString !
+}
+var user1 = new User("Bob", 31);
+var user2 = new User("Bob", 31);
+System.out.println(user1.equals(user2));
+System.out.println(user1.hashCode() == user2.hashCode());
+System.out.println(user1);

guide/chapter12-equals_hashCode_toString.md

@@ -127,4 +127,16 @@ System.out.println(user1);
 
 For a record, the methods `equals()`/`hashCode()` and `toString()` are already provided
 so usually you don't have to provide a new implementation.
-
+```java
+record User(String name, int age) {
+  public User {
+    Objects.requireNonNull(name);
+  }
+  // the compiler automatically adds equals/hashCode/toString !
+}
+var user1 = new User("Bob", 31);
+var user2 = new User("Bob", 31);
+System.out.println(user1.equals(user2));
+System.out.println(user1.hashCode() == user2.hashCode());
+System.out.println(user1);
+```

jupyter/chapter12-equals_hashCode_toString.ipynb

@@ -82,6 +82,14 @@
   "metadata": {},
   "source": ["For a record, the methods `equals()`/`hashCode()` and `toString()` are already provided\n", "so usually you don't have to provide a new implementation.\n"]
 }
+,
+{
+  "cell_type": "code",
+  "execution_count": null,
+  "metadata": {},
+  "outputs": [],
+  "source": ["record User(String name, int age) {\n", "  public User {\n", "    Objects.requireNonNull(name);\n", "  }\n", "  // the compiler automatically adds equals/hashCode/toString !\n", "}\n", "var user1 = new User(\"Bob\", 31);\n", "var user2 = new User(\"Bob\", 31);\n", "System.out.println(user1.equals(user2));\n", "System.out.println(user1.hashCode() == user2.hashCode());\n", "System.out.println(user1);\n"]
+}
 ],
   "metadata": {
     "kernelspec": {