Day 2 Final question

Questions.txt

@@ -501,3 +501,76 @@ D) at line n1
    }
 E) at line n1
    Client {}
+
+Q)
+interface Int1 {
+  default void doStuff() {
+    System.out.println("Int1.doStuff()");
+  }
+}
+class Cl1 implements Int1 {
+  void doStuff() {
+    System.out.println("Cl1.doStuff");
+  }
+}
+What is the result of a call:
+new Cl1().doStuff();
+
+A) Compilation fails
+B) RuntimeException
+C) Int1.doStuff()
+D) Cl1.doStuff()
+E) Int1.doStuff()
+   Cl1.doStuff()
+
+Q) Given:
+interface IntX {
+  default void doStuff() {
+    System.out.println("IntX.doStuff()");
+  }
+}
+interface IntY {
+  default void doStuff() {
+    System.out.println("IntY.doStuff()");
+  }
+}
+class ClQ implements IntX, IntY {}
+
+What is the result of a call:
+new ClQ().doStuff();
+
+A) Compilation fails
+B) RuntimeException
+C) IntX.doStuff()
+D) IntY.doStuff()
+E) C1QdoStuff()
+
+Q) Given:
+class Parent {
+  Parent(int x) { y += x; out.print(", P-c: y is " + y); }
+  static { out.print(", P-si: x is " + Parent.x); }
+  static int x = 99;
+  int y = 100;
+  { y++; out.print(", P-i: y is " + y); }
+}
+class Child extends Parent {
+  int x = 200;
+  static int y = 300;
+  Child() { super(x); }
+  Child(int x) { this(); }
+  { out.print(", C-i x: is " + x); }
+  static { out.print(", C-si: y is " + y); }
+}
+class InitOrder3 {
+  public static void main(String[] args) {
+    out.print("Hello!");
+    new Child(-1);
+    out.println(" Goodbye!");
+  }
+}
+What is the result?
+A) Compilation fails
+B) Exception at runtime
+C) Hello!, P-si: x is 0, C-si: y is 300, P-i: y is 101, P-c: y is 401, C-i x: is 200 Goodbye!
+D) , P-si: x is 0, C-si: y is 300Hello!, P-i: y is 101, P-c: y is 401, C-i x: is 200 Goodbye!
+E) Hello!, P-si: x is 99, C-si: y is 300, P-i: y is 101, P-c: y is 100Goodbye!

src/main/java/defaultmethods/Examples.java

@@ -0,0 +1,27 @@
+package defaultmethods;
+
+interface IntX {
+//  void doStuff();
+  default void doStuff() {
+    System.out.println("IntX.doStuff()");
+  }
+}
+interface IntY {
+//  default void doStuff() {
+//    System.out.println("IntY.doStuff()");
+//  }
+  void doStuff();
+}
+class ClQ implements IntX, IntY {
+  @Override
+  public void doStuff() {
+    IntX.super.doStuff();
+//    IntY.super.doStuff();
+  }
+}
+
+public class Examples {
+  public static void main(String[] args) {
+    new ClQ().doStuff();
+  }
+}

src/main/java/recordstuff/Example.java

@@ -6,6 +6,8 @@
 // has the type of the component (if varags then array)
 // components create final fields with the same name
 // components cannot have the name of an Object method (e.g. wait, toString :)
+// all records are subtypes of java.lang.Record, but MUST NOT use extends
+// and are implicitly final
 record Client(String name, int creditLimit) { // these two are "components"
   // line n1
   // not permitted to add any instance fields
@@ -19,6 +21,44 @@ public String toString() {
 //    return super.toString(); // NOPE, there is no super...
     return "I'm a client with credit " + creditLimit;
   }
+
+  // explicit canonical constructor, must not be less accessible
+  // than the class (default canonical constructor has same access as class
+  // MUST initialize the fields from the components
+  // argument names MUST match the components!!!
+//  public Client(String name, int credit) { // NOPE
+  Client(String name, int creditLimit) {
+//    super(); // NOPE! This must be left to the system
+    // most likely reason to create explicit constructor would be
+    // validation:
+    if (name == null || name.length() == 0) {
+      throw new IllegalArgumentException("bad name");
+    }
+
+    this.name = name;
+    this.creditLimit = creditLimit;
+//    this.creditLimit = credit; // this can't happen
+  }
+
+  // because hand-coded constructor most likely just does validation,
+  // we can define "compact constructor"
+//  Client { // must not have both this compact AND explicit canonical
+//    if (name == null || name.length() == 0) {
+//      throw new IllegalArgumentException("bad name");
+//    }
+//    name = "Mr/Mrs/Ms/Mx " + name; // "Normalization"
+//    // compact constructor MUST NOT mention the fields
+//    // this code "runs into" the default canonical constructor :)
+//  }
+
+  // are allowed overloaded constructors
+  // which are allowed to be less accessible?
+  // all routes through construction MUST end up at the
+  // canonical constructor (whichever form it took)
+  // that's where the final fields are initialized
+  private Client(String name) {
+    this(name, 1000);
+  }
 }
 
 public class Example {