Class Design

Author: turingfly

Java-8/src/advancedClassDesign/HashCode.java

@@ -5,15 +5,17 @@
  * @author chengfeili 
  * Jun 3, 2017 1:30:00 PM
  * 
- *         Whenerver you overfride equals(), 
- *         you are also exprected to override hashCode()
+ *         Whenever you override equals(), 
+ *         you are also expected to override hashCode()
  *         
- *         1. Whithin the same program, the result of hashCode() must not change.
+ *         1. Within the same program, the result of hashCode() must not change.
  *         this means that you sholdn't include variables that change in figuring 
  *         out the hash code.
+ *         
  *         2. If equals() returns true when called with two objects, calling
  *         hashCode() on each of those objects must return the same result.
  *         This means hashCode() can use a subset of the variables that equals uses.
+ *         
  *		   3. If equals returns false when called with two objects, calling hashCode() on each of 
  *		   those objects does not have to return a different result. This means hashCode() results 
  *		   do not need to be unique when called on unequal objects.

Java-8/src/advancedClassDesign/Polymorphism.java

@@ -0,0 +1,57 @@
+package advancedClassDesign;
+
+/**
+ * 
+ * @author chengfeili 
+ * Jun 27, 2017 6:11:11 PM
+ *
+ *         Polymorphism is the ability for an object to vary its behavior based
+ *         on its type
+ * 
+ *         Even though HumanBeing is used, the JVM decides at runtime which
+ *         method to call based on the type of the object assigned, not the
+ *         variable's reference type.
+ * 
+ *         This is called virtual method invocation, a fancy name for
+ *         overriding.
+ * 
+ *         Overriding is also known as dynamic polymorphism because the type of
+ *         the object is decided at RUN time.
+ * 
+ *         In contrast, overloading is also called static polymorphism because
+ *         it's resolved at COMPILE time.
+ */
+public class Polymorphism {
+	public static void main(String[] args) {
+		HumanBeing[] someHumans = new HumanBeing[3];
+		someHumans[0] = new Man();
+		someHumans[1] = new Woman();
+		someHumans[2] = new Baby();
+		for (int i = 0; i < someHumans.length; i++) {
+			someHumans[i].dress();
+			System.out.println();
+		}
+	}
+}
+
+abstract class HumanBeing {
+	public abstract void dress();
+}
+
+class Man extends HumanBeing {
+	public void dress() {
+		System.out.println("Man");
+	}
+}
+
+class Woman extends HumanBeing {
+	public void dress() {
+		System.out.println("Woman");
+	}
+}
+
+class Baby extends HumanBeing {
+	public void dress() {
+		System.out.println("Baby");
+	}
+}