Merge pull request #1 from adambard/master

update

1 files changed, 572 insertions, 166 deletions

diff --git a/java.html.markdown b/java.html.markdown
index 3dd65679..dd875c16 100644
--- a/java.html.markdown
+++ b/java.html.markdown
@@ -1,25 +1,42 @@
 ---
-
 language: java
 contributors:
-    - ["Jake Prather", "http://github.com/JakeHP"]
-    - ["Madison Dickson", "http://github.com/mix3d"]
-    - ["Jakukyo Friel", "http://weakish.github.io"]
+    - ["Jake Prather", "https://github.com/JakeHP"]
+    - ["Jakukyo Friel", "https://weakish.github.io"]
+    - ["Madison Dickson", "https://github.com/mix3d"]
+    - ["Simon Morgan", "https://sjm.io/"]
+    - ["Zachary Ferguson", "https://github.com/zfergus2"]
+    - ["Cameron Schermerhorn", "https://github.com/cschermerhorn"]
+    - ["Rachel Stiyer", "https://github.com/rstiyer"]
+    - ["Michael Dähnert", "https://github.com/JaXt0r"]
+    - ["Rob Rose", "https://github.com/RobRoseKnows"]
+    - ["Sean Nam", "https://github.com/seannam"]
 filename: LearnJava.java
-
 ---
 
-Java is a general-purpose, concurrent, class-based, object-oriented computer programming language.
-[Read more here.](http://docs.oracle.com/javase/tutorial/java/index.html)
+Java is a general-purpose, concurrent, class-based, object-oriented computer
+programming language.
+[Read more here.](https://docs.oracle.com/javase/tutorial/java/)
 
 ```java
 // Single-line comments start with //
+
 /*
 Multi-line comments look like this.
 */
+
 /**
-JavaDoc comments look like this. Used to describe the Class or various
-attributes of a Class.
+ * JavaDoc comments look like this. Used to describe the Class or various
+ * attributes of a Class.
+ * Main attributes:
+ *
+ * @author         Name (and contact information such as email) of author(s).
+ * @version     Current version of the program.
+ * @since        When this part of the program was first added.
+ * @param         For describing the different parameters for a method.
+ * @return        For describing what the method returns.
+ * @deprecated  For showing the code is outdated or shouldn't be used.
+ * @see         Links to another part of documentation.
 */
 
 // Import ArrayList class inside of the java.util package
@@ -27,41 +44,107 @@ import java.util.ArrayList;
 // Import all classes inside of java.security package
 import java.security.*;
 
-// Each .java file contains one outer-level public class, with the same name as
-// the file.
+// Each .java file contains one outer-level public class, with the same name
+// as the file.
 public class LearnJava {
 
-    // A program must have a main method as an entry point
-    public static void main (String[] args) {
+    // In order to run a java program, it must have a main method as an entry
+    // point.
+    public static void main(String[] args) {
 
-        // Use System.out.println to print lines
+    ///////////////////////////////////////
+    // Input/Output
+    ///////////////////////////////////////
+
+        /*
+        * Output
+        */
+
+        // Use System.out.println() to print lines.
         System.out.println("Hello World!");
         System.out.println(
             "Integer: " + 10 +
             " Double: " + 3.14 +
             " Boolean: " + true);
 
-        // To print without a newline, use System.out.print
+        // To print without a newline, use System.out.print().
         System.out.print("Hello ");
         System.out.print("World");
 
+        // Use System.out.printf() for easy formatted printing.
+        System.out.printf("pi = %.5f", Math.PI); // => pi = 3.14159
+
+        /*
+         * Input
+         */
+
+        // use Scanner to read input
+        // must import java.util.Scanner;
+        Scanner scanner = new Scanner(System.in);
+
+        // read string input
+        String name = scanner.next();
+
+        // read byte input
+        byte numByte = scanner.nextByte();
+
+        // read int input
+        int numInt = scanner.nextInt();
+
+        // read long input
+        float numFloat = scanner.nextFloat();
+
+        // read double input
+        double numDouble = scanner.nextDouble();
+
+        // read boolean input
+        boolean bool = scanner.nextBoolean();
 
         ///////////////////////////////////////
-        // Types & Variables
+        // Variables
         ///////////////////////////////////////
 
+        /*
+        *  Variable Declaration
+        */
         // Declare a variable using <type> <name>
+        int fooInt;
+        // Declare multiple variables of the same
+        // type <type> <name1>, <name2>, <name3>
+        int fooInt1, fooInt2, fooInt3;
+
+        /*
+        *  Variable Initialization
+        */
+
+        // Initialize a variable using <type> <name> = <val>
+        int barInt = 1;
+        // Initialize multiple variables of same type with same
+        // value <type> <name1>, <name2>, <name3>
+        // <name1> = <name2> = <name3> = <val>
+        int barInt1, barInt2, barInt3;
+        barInt1 = barInt2 = barInt3 = 1;
+
+        /*
+        *  Variable types
+        */
         // Byte - 8-bit signed two's complement integer
         // (-128 <= byte <= 127)
         byte fooByte = 100;
 
+        // If you would like to interpret a byte as an unsigned integer
+        // then this simple operation can help
+        int unsignedIntLessThan256 = 0xff & fooByte;
+        // this contrasts a cast which can be negative.
+        int signedInt = (int) fooByte;
+
         // Short - 16-bit signed two's complement integer
         // (-32,768 <= short <= 32,767)
         short fooShort = 10000;
 
         // Integer - 32-bit signed two's complement integer
         // (-2,147,483,648 <= int <= 2,147,483,647)
-        int fooInt = 1;
+        int bazInt = 1;
 
         // Long - 64-bit signed two's complement integer
         // (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807)
@@ -69,14 +152,18 @@ public class LearnJava {
         // L is used to denote that this variable value is of type Long;
         // anything without is treated as integer by default.
 
-        // Note: Java has no unsigned types
+        // Note: byte, short, int and long are signed. They can have positive and negative values.
+        // There are no unsigned variants.
+        // char, however, is 16-bit unsigned.
 
         // Float - Single-precision 32-bit IEEE 754 Floating Point
+        // 2^-149 <= float <= (2-2^-23) * 2^127
         float fooFloat = 234.5f;
-        // f is used to denote that this variable value is of type float;
+        // f or F is used to denote that this variable value is of type float;
         // otherwise it is treated as double.
 
         // Double - Double-precision 64-bit IEEE 754 Floating Point
+        // 2^-1074 <= x <= (2-2^-52) * 2^1023
         double fooDouble = 123.4;
 
         // Boolean - true & false
@@ -86,8 +173,38 @@ public class LearnJava {
         // Char - A single 16-bit Unicode character
         char fooChar = 'A';
 
-        // final variables can't be reassigned to another object
+        // final variables can't be reassigned,
         final int HOURS_I_WORK_PER_WEEK = 9001;
+        // but they can be initialized later.
+        final double E;
+        E = 2.71828;
+
+        // BigInteger - Immutable arbitrary-precision integers
+        //
+        // BigInteger is a data type that allows programmers to manipulate
+        // integers longer than 64-bits. Integers are stored as an array of
+        // of bytes and are manipulated using functions built into BigInteger
+        //
+        // BigInteger can be initialized using an array of bytes or a string.
+        BigInteger fooBigInteger = new BigInteger(fooByteArray);
+
+        // BigDecimal - Immutable, arbitrary-precision signed decimal number
+        //
+        // A BigDecimal takes two parts: an arbitrary precision integer
+        // unscaled value and a 32-bit integer scale
+        //
+        // BigDecimal allows the programmer complete control over decimal
+        // rounding. It is recommended to use BigDecimal with currency values
+        // and where exact decimal precision is required.
+        //
+        // BigDecimal can be initialized with an int, long, double or String
+        // or by initializing the unscaled value (BigInteger) and scale (int).
+        BigDecimal fooBigDecimal = new BigDecimal(fooBigInteger, fooInt);
+
+        // Be wary of the constructor that takes a float or double as
+        // the inaccuracy of the float/double will be copied in BigDecimal.
+        // Prefer the String constructor when you need an exact value.
+        BigDecimal tenCents = new BigDecimal("0.1");
 
         // Strings
         String fooString = "My String Is Here!";
@@ -100,19 +217,55 @@ public class LearnJava {
         System.out.println(barString);
         System.out.println(bazString);
 
+        // String Building
+        // #1 - with plus operator
+        // That's the basic way to do it (optimized under the hood)
+        String plusConcatenated = "Strings can " + "be concatenated " + "via + operator.";
+        System.out.println(plusConcatenated);
+        // Output: Strings can be concatenated via + operator.
+
+        // #2 - with StringBuilder
+        // This way doesn't create any intermediate strings. It just stores the string pieces, and ties them together
+        // when toString() is called.
+        // Hint: This class is not thread safe. A thread-safe alternative (with some impact on performance) is StringBuffer.
+        StringBuilder builderConcatenated = new StringBuilder();
+        builderConcatenated.append("You ");
+        builderConcatenated.append("can use ");
+        builderConcatenated.append("the StringBuilder class.");
+        System.out.println(builderConcatenated.toString()); // only now is the string built
+        // Output: You can use the StringBuilder class.
+
+        // StringBuilder is efficient when the fully constructed String is not required until the end of some processing.
+        StringBuilder stringBuilder = new StringBuilder();
+        String inefficientString = "";
+        for (int i = 0 ; i < 10; i++) {
+            stringBuilder.append(i).append(" ");
+            inefficientString += i + " ";
+        }
+        System.out.println(inefficientString);
+        System.out.println(stringBuilder.toString());
+        // inefficientString requires a lot more work to produce, as it generates a String on every loop iteration.
+        // Simple concatenation with + is compiled to a StringBuilder and toString()
+        // Avoid string concatenation in loops.
+
+        // #3 - with String formatter
+        // Another alternative way to create strings. Fast and readable.
+        String.format("%s may prefer %s.", "Or you", "String.format()");
+        // Output: Or you may prefer String.format().
+
         // Arrays
-        //The array size must be decided upon instantiation
-        //The following formats work for declaring an array
-        //<datatype> [] <var name> = new <datatype>[<array size>];
-        //<datatype> <var name>[] = new <datatype>[<array size>];
-        int [] intArray = new int[10];
-        String [] stringArray = new String[1];
-        boolean boolArray [] = new boolean[100];
+        // The array size must be decided upon instantiation
+        // The following formats work for declaring an array
+        // <datatype>[] <var name> = new <datatype>[<array size>];
+        // <datatype> <var name>[] = new <datatype>[<array size>];
+        int[] intArray = new int[10];
+        String[] stringArray = new String[1];
+        boolean boolArray[] = new boolean[100];
 
         // Another way to declare & initialize an array
-        int [] y = {9000, 1000, 1337};
-        String names [] = {"Bob", "John", "Fred", "Juan Pedro"};
-        boolean bools[] = new boolean[] {true, false, false};
+        int[] y = {9000, 1000, 1337};
+        String names[] = {"Bob", "John", "Fred", "Juan Pedro"};
+        boolean bools[] = {true, false, false};
 
         // Indexing an array - Accessing an element
         System.out.println("intArray @ 0: " + intArray[0]);
@@ -121,18 +274,31 @@ public class LearnJava {
         intArray[1] = 1;
         System.out.println("intArray @ 1: " + intArray[1]); // => 1
 
-        // Others to check out
-        // ArrayLists - Like arrays except more functionality is offered,
-        //             and the size is mutable
+        // Other data types worth checking out
+        // ArrayLists - Like arrays except more functionality is offered, and
+        //              the size is mutable.
         // LinkedLists - Implementation of doubly-linked list. All of the
-        //             operations perform as could be expected for
-        //             a doubly-linked list.
-        // Maps - A set of objects that maps keys to values. A map cannot contain
-        //             duplicate keys; each key can map to at most one value.
-        // HashMaps - This class uses a hashtable to implement the Map interface.
-        //             This allows the execution time of basic operations,
-        //             such as get and insert element, to remain constant even
-        //             for large sets. 
+        //               operations perform as could be expected for a
+        //               doubly-linked list.
+        // Maps - A mapping of key Objects to value Objects. Map is
+        //        an interface and therefore cannot be instantiated.
+        //        The type of keys and values contained in a Map must
+        //        be specified upon instantiation of the implementing
+        //        class. Each key may map to only one corresponding value,
+        //        and each key may appear only once (no duplicates).
+        // HashMaps - This class uses a hashtable to implement the Map
+        //            interface. This allows the execution time of basic
+        //            operations, such as get and insert element, to remain
+        //            constant-amortized even for large sets.
+        // TreeMap - A Map that is sorted by its keys. Each modification 
+        //           maintains the sorting defined by either a Comparator
+        //           supplied at instantiation, or comparisons of each Object
+        //           if they implement the Comparable interface.
+        //           Failure of keys to implement Comparable combined with failure to
+        //           supply a Comparator will throw ClassCastExceptions.
+        //           Insertion and removal operations take O(log(n)) time
+        //           so avoid using this data structure unless you are taking
+        //           advantage of the sorting.
 
         ///////////////////////////////////////
         // Operators
@@ -145,7 +311,8 @@ public class LearnJava {
         System.out.println("1+2 = " + (i1 + i2)); // => 3
         System.out.println("2-1 = " + (i2 - i1)); // => 1
         System.out.println("2*1 = " + (i2 * i1)); // => 2
-        System.out.println("1/2 = " + (i1 / i2)); // => 0 (0.5 truncated down)
+        System.out.println("1/2 = " + (i1 / i2)); // => 0 (int/int returns int)
+        System.out.println("1/2.0 = " + (i1 / (double)i2)); // => 0.5
 
         // Modulo
         System.out.println("11%3 = "+(11 % 3)); // => 2
@@ -158,27 +325,32 @@ public class LearnJava {
         System.out.println("2 <= 2? " + (2 <= 2)); // => true
         System.out.println("2 >= 2? " + (2 >= 2)); // => true
 
+        // Boolean operators
+        System.out.println("3 > 2 && 2 > 3? " + ((3 > 2) && (2 > 3))); // => false
+        System.out.println("3 > 2 || 2 > 3? " + ((3 > 2) || (2 > 3))); // => true
+        System.out.println("!(3 == 2)? " + (!(3 == 2))); // => true
+
         // Bitwise operators!
         /*
-        ~       Unary bitwise complement
-        <<      Signed left shift
-        >>      Signed right shift
-        >>>     Unsigned right shift
-        &       Bitwise AND
-        ^       Bitwise exclusive OR
-        |       Bitwise inclusive OR
+        ~      Unary bitwise complement
+        <<     Signed left shift
+        >>     Signed/Arithmetic right shift
+        >>>    Unsigned/Logical right shift
+        &      Bitwise AND
+        ^      Bitwise exclusive OR
+        |      Bitwise inclusive OR
         */
 
-        // Incrementations
+        // Increment operators
         int i = 0;
         System.out.println("\n->Inc/Dec-rementation");
         // The ++ and -- operators increment and decrement by 1 respectively.
         // If they are placed before the variable, they increment then return;
         // after the variable they return then increment.
-        System.out.println(i++); //i = 1, prints 0 (post-increment)
-        System.out.println(++i); //i = 2, prints 2 (pre-increment)
-        System.out.println(i--); //i = 1, prints 2 (post-decrement)
-        System.out.println(--i); //i = 0, prints 0 (pre-decrement)
+        System.out.println(i++); // i = 1, prints 0 (post-increment)
+        System.out.println(++i); // i = 2, prints 2 (pre-increment)
+        System.out.println(i--); // i = 1, prints 2 (post-decrement)
+        System.out.println(--i); // i = 0, prints 0 (pre-decrement)
 
         ///////////////////////////////////////
         // Control Structures
@@ -187,7 +359,7 @@ public class LearnJava {
 
         // If statements are c-like
         int j = 10;
-        if (j == 10){
+        if (j == 10) {
             System.out.println("I get printed");
         } else if (j > 10) {
             System.out.println("I don't");
@@ -197,80 +369,116 @@ public class LearnJava {
 
         // While loop
         int fooWhile = 0;
-        while(fooWhile < 100)
-        {
-            //System.out.println(fooWhile);
-            //Increment the counter
-            //Iterated 100 times, fooWhile 0,1,2...99
+        while(fooWhile < 100) {
+            System.out.println(fooWhile);
+            // Increment the counter
+            // Iterated 100 times, fooWhile 0,1,2...99
             fooWhile++;
         }
         System.out.println("fooWhile Value: " + fooWhile);
 
         // Do While Loop
         int fooDoWhile = 0;
-        do
-        {
-            //System.out.println(fooDoWhile);
-            //Increment the counter
-            //Iterated 99 times, fooDoWhile 0->99
+        do {
+            System.out.println(fooDoWhile);
+            // Increment the counter
+            // Iterated 99 times, fooDoWhile 0->99
             fooDoWhile++;
-        }while(fooDoWhile < 100);
+        } while(fooDoWhile < 100);
         System.out.println("fooDoWhile Value: " + fooDoWhile);
 
         // For Loop
-        int fooFor;
-        //for loop structure => for(<start_statement>; <conditional>; <step>)
-        for(fooFor=0; fooFor<10; fooFor++){
-            //System.out.println(fooFor);
-            //Iterated 10 times, fooFor 0->9
+        // for loop structure => for(<start_statement>; <conditional>; <step>)
+        for (int fooFor = 0; fooFor < 10; fooFor++) {
+            System.out.println(fooFor);
+            // Iterated 10 times, fooFor 0->9
         }
         System.out.println("fooFor Value: " + fooFor);
 
+        // Nested For Loop Exit with Label
+        outer:
+        for (int i = 0; i < 10; i++) {
+          for (int j = 0; j < 10; j++) {
+            if (i == 5 && j ==5) {
+              break outer;
+              // breaks out of outer loop instead of only the inner one
+            }
+          }
+        }
+
         // For Each Loop
-        // An automatic iteration through an array or list of objects.
-        int[] fooList = {1,2,3,4,5,6,7,8,9};
-        //for each loop structure => for(<object> : <array_object>)
-        //reads as: for each object in the array
-        //note: the object type must match the array.
-
-        for( int bar : fooList ){
-            //System.out.println(bar);
+        // The for loop is also able to iterate over arrays as well as objects
+        // that implement the Iterable interface.
+        int[] fooList = {1, 2, 3, 4, 5, 6, 7, 8, 9};
+        // for each loop structure => for (<object> : <iterable>)
+        // reads as: for each element in the iterable
+        // note: the object type must match the element type of the iterable.
+        for (int bar : fooList) {
+            System.out.println(bar);
             //Iterates 9 times and prints 1-9 on new lines
         }
 
         // Switch Case
         // A switch works with the byte, short, char, and int data types.
-        // It also works with enumerated types (discussed in Enum Types),
-        // the String class, and a few special classes that wrap
-        // primitive types: Character, Byte, Short, and Integer.
+        // It also works with enumerated types (discussed in Enum Types), the
+        // String class, and a few special classes that wrap primitive types:
+        // Character, Byte, Short, and Integer.
+        // Starting in Java 7 and above, we can also use the String type.
+        // Note: Do remember that, not adding "break" at end any particular case ends up in
+        // executing the very next case(given it satisfies the condition provided) as well.
         int month = 3;
         String monthString;
-        switch (month){
-            case 1:
-                    monthString = "January";
+        switch (month) {
+            case 1: monthString = "January";
                     break;
-            case 2:
-                    monthString = "February";
+            case 2: monthString = "February";
                     break;
-            case 3:
-                    monthString = "March";
-                    break;
-            default:
-                    monthString = "Some other month";
+            case 3: monthString = "March";
                     break;
+            default: monthString = "Some other month";
+                     break;
         }
         System.out.println("Switch Case Result: " + monthString);
 
+
+        // Try-with-resources (Java 7+)
+        // Try-catch-finally statements work as expected in Java but in Java 7+
+        // the try-with-resources statement is also available. Try-with-resources
+        // simplifies try-catch-finally statements by closing resources
+        // automatically.
+
+        // In order to use a try-with-resources, include an instance of a class
+        // in the try statement. The class must implement java.lang.AutoCloseable.
+        try (BufferedReader br = new BufferedReader(new FileReader("foo.txt"))) {
+            // You can attempt to do something that could throw an exception.
+            System.out.println(br.readLine());
+            // In Java 7, the resource will always be closed, even if it throws
+            // an Exception.
+        } catch (Exception ex) {
+            //The resource will be closed before the catch statement executes.
+            System.out.println("readLine() failed.");
+        }
+        // No need for a finally statement in this case, the BufferedReader is
+        // already closed. This can be used to avoid certain edge cases where
+        // a finally statement might not be called.
+        // To learn more:
+        // https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html
+
+
         // Conditional Shorthand
         // You can use the '?' operator for quick assignments or logic forks.
-        // Reads as "If (statement) is true, use <first value>, otherwise, use <second value>"
+        // Reads as "If (statement) is true, use <first value>, otherwise, use
+        // <second value>"
         int foo = 5;
         String bar = (foo < 10) ? "A" : "B";
-        System.out.println(bar); // Prints A, because the statement is true
-
+        System.out.println("bar : " + bar); // Prints "bar : A", because the 
+        // statement is true.
+        // Or simply
+        System.out.println("bar : " + (foo < 10 ? "A" : "B"));
+        
 
         ////////////////////////////////////////
-        // Converting Data Types And Typecasting
+        // Converting Data Types
         ////////////////////////////////////////
 
         // Converting data
@@ -286,13 +494,6 @@ public class LearnJava {
         // Long
         // String
 
-        // Typecasting
-        // You can also cast java objects, there's a lot of details and
-        // deals with some more intermediate concepts.
-        // Feel free to check it out here:
-        // http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
-
-
         ///////////////////////////////////////
         // Classes And Functions
         ///////////////////////////////////////
@@ -311,17 +512,41 @@ public class LearnJava {
         // toString returns this Object's string representation.
         System.out.println("trek info: " + trek.toString());
 
-    } // End main method
-} // End LearnJava class
+        // Double Brace Initialization
+        // The Java Language has no syntax for how to create static Collections
+        // in an easy way. Usually you end up in the following way:
+        private static final Set<String> COUNTRIES = new HashSet<String>();
+        static {
+           COUNTRIES.add("DENMARK");
+           COUNTRIES.add("SWEDEN");
+           COUNTRIES.add("FINLAND");
+        }
 
+        // But there's a nifty way to achieve the same thing in an
+        // easier way, by using something that is called Double Brace
+        // Initialization.
+        private static final Set<String> COUNTRIES = new HashSet<String>() {{
+            add("DENMARK");
+            add("SWEDEN");
+            add("FINLAND");
+        }}
+
+        // The first brace is creating a new AnonymousInnerClass and the
+        // second one declares an instance initializer block. This block
+        // is called when the anonymous inner class is created.
+        // This does not only work for Collections, it works for all
+        // non-final classes.
 
-// You can include other, non-public outer-level classes in a .java file
+    } // End main method
+} // End LearnJava class
 
+// You can include other, non-public outer-level classes in a .java file,
+// but it is not good practice. Instead split classes into separate files.
 
 // Class Declaration Syntax:
-// <public/private/protected> class <class name>{
-//    //data fields, constructors, functions all inside.
-//    //functions are called as methods in Java.
+// <public/private/protected> class <class name> {
+//    // data fields, constructors, functions all inside.
+//    // functions are called as methods in Java.
 // }
 
 class Bicycle {
@@ -331,31 +556,43 @@ class Bicycle {
     private int speed;  // Private: Only accessible from within the class
     protected int gear; // Protected: Accessible from the class and subclasses
     String name; // default: Only accessible from within this package
+    static String className; // Static class variable
+
+    // Static block
+    // Java has no implementation of static constructors, but
+    // has a static block that can be used to initialize class variables
+    // (static variables).
+    // This block will be called when the class is loaded.
+    static {
+        className = "Bicycle";
+    }
 
     // Constructors are a way of creating classes
     // This is a constructor
     public Bicycle() {
+        // You can also call another constructor:
+        // this(1, 50, 5, "Bontrager");
         gear = 1;
         cadence = 50;
         speed = 5;
         name = "Bontrager";
     }
-
     // This is a constructor that takes arguments
-    public Bicycle(int startCadence, int startSpeed, int startGear, String name) {
+    public Bicycle(int startCadence, int startSpeed, int startGear,
+        String name) {
         this.gear = startGear;
         this.cadence = startCadence;
         this.speed = startSpeed;
         this.name = name;
     }
 
-    // Function Syntax:
+    // Method Syntax:
     // <public/private/protected> <return type> <function name>(<args>)
 
     // Java classes often implement getters and setters for their fields
 
     // Method declaration syntax:
-    // <scope> <return type> <method name>(<args>)
+    // <access modifier> <return type> <method name>(<args>)
     public int getCadence() {
         return cadence;
     }
@@ -364,34 +601,27 @@ class Bicycle {
     public void setCadence(int newValue) {
         cadence = newValue;
     }
-
     public void setGear(int newValue) {
         gear = newValue;
     }
-
     public void speedUp(int increment) {
         speed += increment;
     }
-
     public void slowDown(int decrement) {
         speed -= decrement;
     }
-
     public void setName(String newName) {
         name = newName;
     }
-
     public String getName() {
         return name;
     }
 
     //Method to display the attribute values of this Object.
-    @Override
+    @Override // Inherited from the Object class.
     public String toString() {
-        return "gear: " + gear +
-                " cadence: " + cadence +
-                " speed: " + speed +
-                " name: " + name;
+        return "gear: " + gear + " cadence: " + cadence + " speed: " + speed +
+            " name: " + name;
     }
 } // end class Bicycle
 
@@ -400,65 +630,236 @@ class PennyFarthing extends Bicycle {
     // (Penny Farthings are those bicycles with the big front wheel.
     // They have no gears.)
 
-    public PennyFarthing(int startCadence, int startSpeed){
+    public PennyFarthing(int startCadence, int startSpeed) {
         // Call the parent constructor with super
         super(startCadence, startSpeed, 0, "PennyFarthing");
     }
 
-    // You should mark a method you're overriding with an @annotation
-    // To learn more about what annotations are and their purpose
-    // check this out: http://docs.oracle.com/javase/tutorial/java/annotations/
+    // You should mark a method you're overriding with an @annotation.
+    // To learn more about what annotations are and their purpose check this
+    // out: http://docs.oracle.com/javase/tutorial/java/annotations/
     @Override
     public void setGear(int gear) {
-        gear = 0;
+        this.gear = 0;
     }
-
 }
 
-//Interfaces
-//Interface declaration syntax
-//<access-level> interface <interface-name> extends <super-interfaces> {
-//		//Constants
-//		//Method declarations
-//}
+// Object casting
+// Since the PennyFarthing class is extending the Bicycle class, we can say
+// a PennyFarthing is a Bicycle and write :
+// Bicycle bicycle = new PennyFarthing();
+// This is called object casting where an object is taken for another one. There
+// are lots of details and deals with some more intermediate concepts here:
+// https://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
+
+// Interfaces
+// Interface declaration syntax
+// <access-level> interface <interface-name> extends <super-interfaces> {
+//     // Constants
+//     // Method declarations
+// }
 
-//Example - Food:
+// Example - Food:
 public interface Edible {
-	public void eat(); //Any class that implements this interface, must implement this method
+    public void eat(); // Any class that implements this interface, must
+                       // implement this method.
 }
 
 public interface Digestible {
-	public void digest();
+    public void digest();
+    // Since Java 8, interfaces can have default method.
+    public default void defaultMethod() {
+        System.out.println("Hi from default method ...");
+    }
 }
 
-
-//We can now create a class that implements both of these interfaces
+// We can now create a class that implements both of these interfaces.
 public class Fruit implements Edible, Digestible {
     @Override
-	public void eat() {
-		//...
-	}
+    public void eat() {
+        // ...
+    }
 
     @Override
-	public void digest() {
-		//... 
-	}
+    public void digest() {
+        // ...
+    }
 }
 
-//In java, you can extend only one class, but you can implement many interfaces.
-//For example:
-public class ExampleClass extends ExampleClassParent implements InterfaceOne, InterfaceTwo {
+// In Java, you can extend only one class, but you can implement many
+// interfaces. For example:
+public class ExampleClass extends ExampleClassParent implements InterfaceOne,
+    InterfaceTwo {
+    @Override
+    public void InterfaceOneMethod() {
+    }
+
     @Override
-	public void InterfaceOneMethod() {
+    public void InterfaceTwoMethod() {
+    }
 
-	}
+}
+
+// Abstract Classes
+
+// Abstract Class declaration syntax
+// <access-level> abstract class <abstract-class-name> extends
+// <super-abstract-classes> {
+//     // Constants and variables
+//     // Method declarations
+// }
 
+// Abstract Classes cannot be instantiated.
+// Abstract classes may define abstract methods.
+// Abstract methods have no body and are marked abstract
+// Non-abstract child classes must @Override all abstract methods
+// from their super-classes.
+// Abstract classes can be useful when combining repetitive logic
+// with customised behavior, but as Abstract classes require
+// inheritance, they violate "Composition over inheritance"
+// so consider other approaches using composition.
+// https://en.wikipedia.org/wiki/Composition_over_inheritance
+
+public abstract class Animal
+{
+    private int age;
+
+    public abstract void makeSound();
+
+    // Method can have a body
+    public void eat()
+    {
+        System.out.println("I am an animal and I am Eating.");
+        // Note: We can access private variable here.
+        age = 30;
+    }
+
+    public void printAge()
+    {
+        System.out.println(age);
+    }
+
+    // Abstract classes can have main method.
+    public static void main(String[] args)
+    {
+        System.out.println("I am abstract");
+    }
+}
+
+class Dog extends Animal
+{
+    // Note still have to override the abstract methods in the
+    // abstract class.
     @Override
-	public void InterfaceTwoMethod() {
+    public void makeSound()
+    {
+        System.out.println("Bark");
+        // age = 30;    ==> ERROR!    age is private to Animal
+    }
 
-	}
+    // NOTE: You will get an error if you used the
+    // @Override annotation here, since java doesn't allow
+    // overriding of static methods.
+    // What is happening here is called METHOD HIDING.
+    // Check out this SO post: http://stackoverflow.com/questions/16313649/
+    public static void main(String[] args)
+    {
+        Dog pluto = new Dog();
+        pluto.makeSound();
+        pluto.eat();
+        pluto.printAge();
+    }
 }
 
+// Final Classes
+
+// Final Class declaration syntax
+// <access-level> final <final-class-name> {
+//     // Constants and variables
+//     // Method declarations
+// }
+
+// Final classes are classes that cannot be inherited from and are therefore a
+// final child. In a way, final classes are the opposite of abstract classes
+// because abstract classes must be extended, but final classes cannot be
+// extended.
+public final class SaberToothedCat extends Animal
+{
+    // Note still have to override the abstract methods in the
+    // abstract class.
+    @Override
+    public void makeSound()
+    {
+        System.out.println("Roar");
+    }
+}
+
+// Final Methods
+public abstract class Mammal()
+{
+    // Final Method Syntax:
+    // <access modifier> final <return type> <function name>(<args>)
+
+    // Final methods, like, final classes cannot be overridden by a child
+    // class, and are therefore the final implementation of the method.
+    public final boolean isWarmBlooded()
+    {
+        return true;
+    }
+}
+
+// Enum Type
+//
+// An enum type is a special data type that enables for a variable to be a set
+// of predefined constants. The variable must be equal to one of the values
+// that have been predefined for it. Because they are constants, the names of
+// an enum type's fields are in uppercase letters. In the Java programming
+// language, you define an enum type by using the enum keyword. For example,
+// you would specify a days-of-the-week enum type as:
+public enum Day {
+    SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
+    THURSDAY, FRIDAY, SATURDAY
+}
+
+// We can use our enum Day like that:
+public class EnumTest {
+    // Variable Enum
+    Day day;
+
+    public EnumTest(Day day) {
+        this.day = day;
+    }
+
+    public void tellItLikeItIs() {
+        switch (day) {
+            case MONDAY:
+                System.out.println("Mondays are bad.");
+                break;
+            case FRIDAY:
+                System.out.println("Fridays are better.");
+                break;
+            case SATURDAY:
+            case SUNDAY:
+                System.out.println("Weekends are best.");
+                break;
+            default:
+                System.out.println("Midweek days are so-so.");
+                break;
+        }
+    }
+
+    public static void main(String[] args) {
+        EnumTest firstDay = new EnumTest(Day.MONDAY);
+        firstDay.tellItLikeItIs(); // => Mondays are bad.
+        EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
+        thirdDay.tellItLikeItIs(); // => Midweek days are so-so.
+    }
+}
+
+// Enum types are much more powerful than we show above.
+// The enum body can include methods and other fields.
+// You can see more at https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
+
 ```
 
 ## Further Reading
@@ -467,22 +868,26 @@ The links provided here below are just to get an understanding of the topic, fee
 
 **Official Oracle Guides**:
 
-* [Java Tutorial Trail from Sun / Oracle](http://docs.oracle.com/javase/tutorial/index.html)
+* [Java Tutorial Trail from Sun / Oracle](https://docs.oracle.com/javase/tutorial/index.html)
+
+* [Java Access level modifiers](https://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html)
 
-* [Java Access level modifiers](http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html)
+* [Object-Oriented Programming Concepts](https://docs.oracle.com/javase/tutorial/java/concepts/index.html):
+    * [Inheritance](https://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html)
+    * [Polymorphism](https://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html)
+    * [Abstraction](https://docs.oracle.com/javase/tutorial/java/IandI/abstract.html)
 
-* [Object-Oriented Programming Concepts](http://docs.oracle.com/javase/tutorial/java/concepts/index.html):
-    * [Inheritance](http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html)
-    * [Polymorphism](http://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html)
-    * [Abstraction](http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html)
+* [Exceptions](https://docs.oracle.com/javase/tutorial/essential/exceptions/index.html)
 
-* [Exceptions](http://docs.oracle.com/javase/tutorial/essential/exceptions/index.html)
+* [Interfaces](https://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html)
 
-* [Interfaces](http://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html)
+* [Generics](https://docs.oracle.com/javase/tutorial/java/generics/index.html)
 
-* [Generics](http://docs.oracle.com/javase/tutorial/java/generics/index.html)
+* [Java Code Conventions](https://www.oracle.com/technetwork/java/codeconvtoc-136057.html)
 
-* [Java Code Conventions](http://www.oracle.com/technetwork/java/codeconv-138413.html)
+* New features in Java 8:
+    * [Lambda expressions (functional programming)](https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html)
+    * [Date and time API (java.time package)](http://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html)
 
 **Online Practice and Tutorials**
 
@@ -490,13 +895,14 @@ The links provided here below are just to get an understanding of the topic, fee
 
 * [Codingbat.com](http://codingbat.com/java)
 
+* [Codewars - Java Katas](https://www.codewars.com/?language=java)
 
 **Books**:
 
 * [Head First Java](http://www.headfirstlabs.com/books/hfjava/)
 
-* [Objects First with Java](http://www.amazon.com/Objects-First-Java-Practical-Introduction/dp/0132492660)
-
-* [Java The Complete Reference](http://www.amazon.com/gp/product/0071606300)
+* [Thinking in Java](http://www.mindview.net/Books/TIJ/)
 
+* [Objects First with Java](https://www.amazon.com/Objects-First-Java-Practical-Introduction/dp/0132492660)
 
+* [Java The Complete Reference](https://www.amazon.com/gp/product/0071606300)