Day 1 final

Questions.txt

@@ -209,3 +209,64 @@ B) s2 == s3
 C) s1 == s3
 D) X.h == s1
 E) None of the above
+
+Q)   Given
+class Thing {
+  int x = 99;
+
+  static void showIt() {
+    int x = 98;
+    System.out.println("x is " + x);
+  }
+}
+
+What is the effect of:
+
+Thing.showIt();
+
+A) Compilation fails
+B) Exception
+C) 99
+D) 98
+
+Q) Given:
+     class Base {
+       void doBaseStuff() { System.out.println("doBaseStuff"); }
+     }
+and:
+     class Sub extends Base {
+       void doBaseStuff() { System.out.println("doSubStuff"); }
+       void doOtherStuff() { System.out.println("doOtherStuff"); }
+     }
+and:
+       Base b = new Sub();
+       ((Runnable) b).run();
+
+What is the result?
+A) doSubStuff
+B) doOtherStuff
+C) doBaseStuff
+D) Exception at runtime
+E) Compilation failure
+
+Q) Given:
+    Object obj = "Hello";
+    boolean answered = false;
+    if (obj instanceof String) {
+      String str = (String)obj;
+      if (str.length() > 3) {
+        System.out.println(str);
+        answered = true;
+      }
+    }
+    if (!answered) System.out.println("Nope");
+
+Which replace the if clause to produce the same output?
+A)    System.out.println(obj instanceof String str && str.length() > 3 ? str : "Nope");
+B)    if (obj instanceof String str when str.length() > 3) System.out.println(str);
+      else System.out.println("Nope");
+C)    if (obj instanceof String str if str.length() > 3) System.out.println(str);
+      else System.out.println("Nope");
+D)    System.out.println(obj instanceof String.class str && str.length() > 3 ? str : "Nope");
+E)    if (!(obj instanceof String str) || str.length() <= 3) System.out.println("Nope");
+      else System.out.println(str);

src/main/java/casting/Ex.java

@@ -0,0 +1,31 @@
+package casting;
+
+public class Ex {
+  public static void main(String[] args) {
+//    Base b = new Sub();
+    Base b = new Base();
+    // compiler allows methods know to be valid based on
+    // COMPILE-TIME type of the reference...
+    // but BEHAVIOR is based on RUNTIME type of the object
+    b.doBaseStuff();
+//    ((Sub)b).doOtherStuff();
+    // impossible casts are rejected by the compiler
+//    ((String)b).length();
+
+    ((Runnable) b).run();
+  }
+}
+
+/*final*/ class Base {
+  void doBaseStuff() { System.out.println("doBaseStuff"); }
+}
+
+//class Sub extends Base implements Runnable {
+//  void doBaseStuff() { System.out.println("doSubStuff"); }
+//  void doOtherStuff() { System.out.println("doOtherStuff"); }
+//
+//  @Override
+//  public void run() {
+//
+//  }
+//}

src/main/java/casting/PatternOne.java

@@ -0,0 +1,28 @@
+package casting;
+
+public class PatternOne {
+  public static void main(String[] args) {
+    Object obj = "Hello";
+    boolean answered = false;
+    if (obj instanceof String) {
+      String str = (String)obj;
+      if (str.length() > 3) {
+        System.out.println(str);
+        answered = true;
+      }
+    }
+    if (!answered) System.out.println("Nope");
+
+    System.out.println("------------");
+
+    // this is still a boolean expression!!!
+    // Look into this Tuesday :)
+    if (obj instanceof String str) {
+      if (str.length() > 3) {
+        System.out.println(str);
+        answered = true;
+      }
+    }
+    if (!answered) System.out.println("Nope");
+  }
+}

src/main/java/intern/UseInteger.java

@@ -0,0 +1,15 @@
+package intern;
+
+public class UseInteger {
+  public static void main(String[] args) {
+    // autoboxed Integer in range of byte (-128 +127) are pooled
+//    Integer i1 = 99;
+//    Integer i2 = 99;
+    Integer i1 = Integer.valueOf(99); // this is what autoboxing creates
+//    Integer i1 = new Integer(99); // this is deprecated DON'T use constructor
+    Integer i2 = 99;
+    Integer i3 = 100;
+    System.out.println(i1 == i2);
+    System.out.println(i1 == i3);
+  }
+}

src/main/java/unqualified/Identifiers.java

@@ -0,0 +1,31 @@
+package unqualified;
+
+public class Identifiers {
+  public static void main(String[] args) {
+//    Thing.showIt();
+  }
+}
+class PThing {
+  static int x = 99;
+}
+class Thing extends PThing {
+  int x = 99;
+//  static int x = 99;
+
+  void showIt() {
+//    int x = 98;
+//    Thing t = new Thing();
+    System.out.println("x is " + x);
+  }
+}
+
+/*
+Unqualified resolution:
+- local item
+- (if no local)
+- for each level of class hierarchy until successful
+-- if instance scope (i.e. there is a "this" available)
+  -- try implied this. prefix
+-- try THIS classname implied prefix
+
+ */