[java/en] few changes (#2788)

java.html.markdown

@@ -50,7 +50,7 @@ public class LearnJava {
 
     // In order to run a java program, it must have a main method as an entry
     // point.
-    public static void main (String[] args) {
+    public static void main(String[] args) {
 
     ///////////////////////////////////////
     // Input/Output
@@ -120,7 +120,8 @@ public class LearnJava {
         // Initialize a variable using <type> <name> = <val>
         int barInt = 1;
         // Initialize multiple variables of same type with same
-        // value <type> <name1>, <name2>, <name3> = <val>
+        // value <type> <name1>, <name2>, <name3>
+        // <name1> = <name2> = <name3> = <val>
         int barInt1, barInt2, barInt3;
         barInt1 = barInt2 = barInt3 = 1;
 
@@ -237,7 +238,7 @@ public class LearnJava {
         // 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++){
+        for (int i = 0 ; i < 10; i++) {
             stringBuilder.append(i).append(" ");
             inefficientString += i + " ";
         }
@@ -416,6 +417,7 @@ public class LearnJava {
         // 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.
         int month = 3;
         String monthString;
         switch (month) {
@@ -430,23 +432,6 @@ public class LearnJava {
         }
         System.out.println("Switch Case Result: " + monthString);
 
-        // Starting in Java 7 and above, switching Strings works like this:
-        String myAnswer = "maybe";
-        switch(myAnswer) {
-            case "yes":
-                System.out.println("You answered yes.");
-                break;
-            case "no":
-                System.out.println("You answered no.");
-                break;
-            case "maybe":
-                System.out.println("You answered maybe.");
-                break;
-            default:
-                System.out.println("You answered " + myAnswer);
-                break;
-        }
-        
 
         // Try-with-resources (Java 7+)
         // Try-catch-finally statements work as expected in Java but in Java 7+
@@ -456,7 +441,7 @@ public class LearnJava {
 
         // 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"))) {
+        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
@@ -481,7 +466,7 @@ public class LearnJava {
         System.out.println(bar); // Prints A, because the statement is true
 
         ////////////////////////////////////////
-        // Converting Data Types And Typecasting
+        // Converting Data Types
         ////////////////////////////////////////
 
         // Converting data
@@ -497,11 +482,6 @@ 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:
-        // https://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
-
         ///////////////////////////////////////
         // Classes And Functions
         ///////////////////////////////////////
@@ -652,6 +632,14 @@ class PennyFarthing extends Bicycle {
     }
 }
 
+// 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> {
@@ -667,10 +655,10 @@ public interface Edible {
 
 public interface Digestible {
     public void digest();
-    // In Java 8, interfaces can have default method.
+    // Since Java 8, interfaces can have default method.
-    // public void digest() {
+    public void defaultMethod() {
-    //     System.out.println("digesting ...");
+        System.out.println("Hi from default method ...");
-    // }
+    }
 }
 
 // We can now create a class that implements both of these interfaces.
@@ -703,14 +691,15 @@ public class ExampleClass extends ExampleClassParent implements InterfaceOne,
 // Abstract Classes
 
 // Abstract Class declaration syntax
-// <access-level> abstract <abstract-class-name> extends <super-abstract-classes> {
+// <access-level> abstract class <abstract-class-name> extends
+// <super-abstract-classes> {
 //     // Constants and variables
 //     // Method declarations
 // }
 
-// Marking a class as abstract means that it contains abstract methods that
+// Marking a class as abstract means that it contains at least one abstract
-// must be defined in a child class. Similar to interfaces, abstract classes
+// method that must be defined in a child class. Similar to interfaces, abstract
-// cannot be instantiated, but instead must be extended and the abstract
+// classes cannot be instantiated, but instead must be extended and the abstract
 // methods defined. Different from interfaces, abstract classes can contain a
 // mixture of concrete and abstract methods. Methods in an interface cannot
 // have a body, unless the method is static, and variables are final by default,