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authorbk2dcradle <ankitsultana@gmail.com>2015-10-04 01:47:09 +0530
committerbk2dcradle <ankitsultana@gmail.com>2015-10-04 18:30:19 +0530
commit6b6f88c64d9a4b2d26de5725dee24f3c459fb93c (patch)
tree01d87771f6d83a7d1c4f2e580f54137e3daf66f3
parenta743c831a07f5e846051b156152fe8e6ddcfb097 (diff)
Added abstract classes
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diff --git a/java.html.markdown b/java.html.markdown
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@@ -451,6 +451,74 @@ public class ExampleClass extends ExampleClassParent implements InterfaceOne,
public void InterfaceTwoMethod() {
}
}
+
+
+// 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 initialise, however in an interface
+ // a variable is implicitly final and hence has
+ // to be initialised.
+ 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();
+ }
+}
+
```
## Further Reading