diff options
Diffstat (limited to 'java.html.markdown')
-rw-r--r-- | java.html.markdown | 119 |
1 files changed, 117 insertions, 2 deletions
diff --git a/java.html.markdown b/java.html.markdown index 5e580f33..34da903a 100644 --- a/java.html.markdown +++ b/java.html.markdown @@ -50,10 +50,30 @@ public class LearnJava { System.out.printf("pi = %.5f", Math.PI); // => pi = 3.14159 /////////////////////////////////////// - // 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 fooInt = 1; + // Initialize multiple variables of same type with same value <type> <name1>, <name2>, <name3> = <val> + int fooInt1, fooInt2, fooInt3; + fooInt1 = fooInt2 = fooInt3 = 1; + + /* + * Variable types + */ // Byte - 8-bit signed two's complement integer // (-128 <= byte <= 127) byte fooByte = 100; @@ -316,6 +336,33 @@ public class LearnJava { // toString returns this Object's string representation. System.out.println("trek info: " + trek.toString()); + + // 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 { + validCodes.add("DENMARK"); + validCodes.add("SWEDEN"); + validCodes.add("FINLAND"); + } + + // But there's a nifty way to achive the same thing in an + // easier way, by using something that is called Double Brace + // Initialization. + + private static final Set<String> COUNTRIES = HashSet<String>() {{ + add("DENMARK"); + add("SWEDEN"); + add("FINLAND"); + }} + + // The first brace is creating an new AnonymousInnerClass and the + // second one declares and instance initializer block. This block + // is called with the anonymous inner class is created. + // This does not only work for Collections, it works for all + // non-final classes. } // End main method } // End LearnJava class @@ -466,6 +513,7 @@ public class ExampleClass extends ExampleClassParent implements InterfaceOne, } } +<<<<<<< HEAD // There are also two special types of classes, abstract and final. // Marking a class as abstract means that it contains abstract methods that must @@ -501,6 +549,73 @@ public final class SaberToothedCat extends Mammal { return "Smilodon fatalis"; } +======= + +// Abstract Classes +// Abstract Class declaration syntax +// <access-level> abstract <abstract-class-name> extends <super-abstract-classes> { +// // Constants and variables +// // Method declarations +// } + +// Methods can't have bodies in an interface, unless the method is +// static. Also variables are NOT final by default, unlike an interface. +// Also abstract classes CAN have the "main" method. +// Abstract classes solve these problems. + +public abstract class Animal +{ + 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; + } + + // No need to initialize, however in an interface + // a variable is implicitly final and hence has + // to be initialized. + private int age; + + public void printAge() + { + System.out.println(age); + } + + // Abstract classes can have main function. + 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 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 awesome SO post: http://stackoverflow.com/questions/16313649/ + public static void main(String[] args) + { + Dog pluto = new Dog(); + pluto.makeSound(); + pluto.eat(); + pluto.printAge(); + } +>>>>>>> adambard/master } ``` |