Java Learn The Basic In 3 Days David Chang Contents 1. Fundamentals of Object Oriented Programming 1.1 Introduction (OOP) 1.2 Objects and Classes 1.3 Data Abstraction 1.4 Encapsulation 1.5 Polymorphism 1.6 Inheritance 2. Introduction to Java 2.1 History of Java 2.2 Basic features of Java 2.3 Compiler and Interpreter 2.4 The JVM 2.5 The Java Runtime Environment (JRE) 2.6 The Java Development Kit (JDK) 2.7 Reserved Words 3. Data Types and Tokens in Java 3.1 Data Types 3.2 Java Tokens 4. Operators and Expressions 4.1 Types of Operators 4.2 Expressions 5. Conditional and Decision Making Statement 5.1 Programming by using assignment statement 5.2 Programming using Streams 5.3 Declarations while using streams 5.4 Decision Making In Java 6. Looping 6.1 Looping Structure 6.2 Types of Loops 7. Array 7.1 Types of Array 7.2 Declaration of an Array 7.3 Passing an Array to a Method 7.4 Basic Operations on Java : Searching and Sorting 8. Classes, Objects and Methods 8.1 Classes in Java 8.2 Creating an Object 8.3 Methods 8.4 Creating Methods 8.5 Method Calling 8.6 Method Overloading 8.7 Method Overriding 9. Interfaces and Packages 9.1 Interfaces 9.2 Packages in Java 9.3 Advantages of Java Package 10. Constructors 10.1 Types of Constructors 11. Thread and Multithread in Java 11.1 Lifecycle of a Thread 11.2 Commonly used methods of Thread class 11.3 Creating Thread 11.4 Multithreading 12. Handling Exceptions and Errors 12.1 Exception Handling with try-catch 12.2 Exception Handling with throws keyword 12.3 Advantages of Exception Handling in Java 12.4 Errors 12.5 Difference between Errors and Exceptions 13. Some Questions and Answers Chapter 1 FUNDAMENTALS OF OBJECT ORIENTED PROGRAMMING 1.1 INTRODUCTION (OOP) Object Oriented Programming (OOP) is an approach to standardize the programs by creating partitioned memory area for both data and method. It has been developed to increase the programmer's productivity and also to overcome the traditional approach of programming. The different Object Oriented Programming languages are C++, Java, Simula-67, etc. An Object Oriented Programming (OOP) allows the data to be applied within designated program area. It gives more significance to data rather than Methods which means it also provides the reusability feature to develop productive logic. FEATURES OF OBJECT ORIENTED PROGRAMMING (OOP) The objects can be used as a bridge to have data flow from one method to another. It gives importance to data items rather than methods. It makes the complete program simpler by dividing it into a number of objects. Data can be easily modified without any change in the method. PRINCIPLES OF (OOP) Objects Classes Data Abstraction Encapsulation Data Hiding Inheritance Polymorphism 1.2 OBJECTS AND CLASSES OBJECTS Object is a unique entity which contains data and methods (characteristics and behavior) together in an Object Oriented Programming (OOP) Language. Example: Let us consider the real world objects, which are visible before us. Any object in the real world can possess the following characteristics: It is visible. It can be described easily. You can observe that the above mentioned criteria has unique identity, definite state, or characteristics and behaviors. For example consider an object Bed: It has the following characteristics: It has four legs. It has a plain top. And the behaviors are: It is used to sleep. It is used to sit. In Payroll system, an employee may be taken as an example of object where characteristics are name, designation, basic pay and behavior as calculating gross pay, provident fund, printing pay slip, etc. CLASSES Class is a set of different objects. Class can contain fields and methods to explain about the behavior of an object. Each object of a class possesses same attributes and behavior defined within the same class. Class is also termed as Object factory. For Example: If Rainbow is the class then the colors in the rainbow represent the different objects of the class Rainbow. Similarly, we can consider a class named fruit where apple, mango, orange are members of the class fruit. If fruit is defined as a class, then the statement: fruit apple = new fruit(); will create an object apple belonging to the class fruit. 1.3 DATA ABSTRACTION Abstraction refers to the act of representing essential features (relevant data) without including background details in order to reduce complexity and increase efficiency. Abstraction is the absolute property of a class. The class binds the data items and functions to promote abstraction. The data members are accessed only through the related methods. A class uses the property of abstraction called as abstract data type. For Example: For driving a car, you only use the essential features without knowing in details the internal mechanism of the system. You can apply brake to stop the car, press accelerator to speed up the car and press clutch to change the gears. Do you ever think what changes are taking place in the machinery part of the engine? The answer is simply No. This act of driving a car is termed as abstraction. 1.4 ENCAPSULATION Encapsulation is the system of wrapping up of data and functions into a single unit (called class). For Data Hiding Encapsulation run on an important OOP concept. In Object Oriented Programming (OOP), data cannot move freely from method to method. They are kept in the corresponding classes in such a way that they will not be accessible to the outside world except by using them through the related methods. It is the most important feature of a class. The functions used in a class can only access the data items. These functions provide interface between data items of the objects and the calling program. Such insulation of data, which cannot be accessed directly outside class premises although they are available in the same program, is known as DATA HIDING. 1.5 POLYMORPHISM The literal meaning of Polymorphism is “available in many forms”. Suppose you have developed a method to perform the addition then it will find the sum of two numbers passed to the method. In case the passed arguments are strings, the function will produce the concatenated (joined) string. Hence, Polymorphism is the ability of different objects to respond, each in its own way, to identical messages. It allows the use of different internal structure of the object by keeping the same external interface. 1.6 INHERITANCE Inheritance can be defined as the process by which objects of one class can link and share some common properties of objects from another class. An object of a class acquires some properties from the objects of another class. Superclass or base class is a class that used as basis for inheritance. Subclass or derived class is known as a class that inherits from a superclass. BENEFITS OF OBJECT ORIENTED PROGRAMMING (OOP) Some benefits of OOP are as listed below: You can create different modules in your project through objects. You can extend the use of existing class through inheritance. Using the concept data hiding can generate secured program. It is highly beneficial to solve complex problems. It is easy to modify and maintain software complexity.