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-rw-r--r--java.html.markdown119
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
}
```