The key benefits are: Re-use of previous work: using implementation inheritance and object composition. Real mapping to the problem domain: Objects map to real world and represent vehicles, customers, products etc: with encapsulation. Modular Architecture: Objects, systems, frameworks etc are the building blocks of larger systems. The increased quality and… Continue reading
The Object Oriented Programming Languages directly represent the real life objects like Car, Jeep, Account, Customer etc. The features of the OO programming languages like polymorphism, inheritance and encapsulation make it powerful. [Tip: remember pie which, stands for Polymorphism, Inheritance and Encapsulation are the 3 pillars of OOPL]
If a class called “SpecialPet” extends your “Pet” class then you can use the keyword “super” to invoke the superclass’s constructor. E.g. public SpecialPet(int id) { super(id); //must be the very first statement in the constructor. } To call a regular method in the super class use: “super.myMethod( );”. This… Continue reading
Yes, by using this() syntax. E.g. public Pet(int id) { this.id = id; // “this” means this object } public Pet (int id, String type) { this(id); // calls constructor public Pet(int id) this.type = type; // ”this” means this object }
Java does not actually require an explicit constructor in the class description. If you do not include a constructor, the Java compiler will create a default constructor in the byte code with an empty argument. This default constructor is equivalent to the explicit “Pet(){}”. If a class includes one or… Continue reading
Constructors Regular methods Constructors must have the same name as the class name and cannot return a value. The constructors are called only once per creation of an object while regular methods can be called many times. E.g. for a Pet.class public Pet() {} // constructor Regular methods can have… Continue reading
When a class is loaded, all blocks that are declared static and don’t have function name (i.e. static initializers) are executed even before the constructors are executed. As the name suggests they are typically used to initialize static fields. public class StaticInitializer { public static final int A = 5;… Continue reading
Static class loading Dynamic class loading Classes are statically loaded with Java’s “new” operator. class MyClass { public static void main(String args[]) { Car c = new Car(); } } Dynamic loading is a technique for programmatically invoking the functions of a class loader at run time. Let us look… Continue reading
Say, you have a class named “Pet” in a project folder “c:\myProject” and package named com.xyz.client, will you be able to compile and run it as it is? package com.xyz.client; public class Pet { public static void main(String[] args) { System.out.println(“I am found in the classpath”); } } To run:… Continue reading
Class loaders are hierarchical. Classes are introduced into the JVM as they are referenced by name in a class that is already running in the JVM. So, how is the very first class loaded? The very first class is especially loaded with the help of static main( ) method declared… Continue reading