Java Learn Java in 3 Days! (David Chang - Programming )

Java Learn The Basic In 3 Days David Chang

Contents 1. Fundamentals of Object Oriented Programming 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.

Chapter 2 INTRODUCTION TO JAVA 2.1 HISTORY OF JAVA Java programming language was originally developed by James Gosling at Sun Microsystems  (Broomfield, Colorado, USA) and released in 1995 as a core component of Sun Microsystems' Java platform. This language was initially called Oak (named after the Oak trees outside Gosling’s office).The platform independence is one of the most significant advantage that JAVA has over other languages. JAVA encapsulates many features of C++. Originally JAVA was designed to execute applets, downloaded while Web browsing. But gradually, the language has been gaining wide acceptance as a programming language, very often replacing C or C++. 2.2 BASIC FEATURES OF JAVA JAVA possesses the following features: Java is not a purely Object Oriented Programming language. Java programs are both compiled and interpreted. It can access data from a local system as well as from net. Java programming is written within a class. The variables and functions are declared and defined with the class. Java programs can create Applets (the programs which run on Webbrowsers). Java is case sensitive language. It distinguishes the upper case and lower case letters.

2.3 COMPILER AND INTERPRETER  All high level languages need to be converted into machine code so that the computer understands the program after taking the required inputs. The conversion of high-level language to machine-level language can be done in two possible ways. It can be done either by using a Compiler or an Interpreter.

The software, by which the conversion of the high level instructions is performed line by line to machine level language, is known as an Interpreter. If an error is found on any line, further execution stops till it is corrected. This process of error correction is much easier but the program takes longer time to execute successfully. SOURCE CODE -> COMPILER/INTERPRETER -> MACHINE CODE However, if all the instructions are converted to machine level language at once and all the errors are listed together, then the software is known as Compiler. This process is much faster but sometimes it becomes difficult to debug all the errors together in a program. The Java source code and Java bytecodes are compiles in  javac command. Compilation Syntax: javac filename.java

2.4 THE JVM JAVA is a high level language (HLL)and the program written in HLL is compiled and then converted to an intermediate language called Byte Code. Byte code makes a Java program highly portable as its Bytes code can easily be transferred from one system to another. When this Byte code is to be run on any other system, an interpreter, known as Java Virtual Machine is needed which translates the byte code to machine code.

Java machine code varies from different platforms like Windows 98, Unix System, etc. Hence, JVM acts as a virtual processor and converts the byte code to the machine code for concerning platform. That is why it is called Java Virtual Machine. Three notions of JVM are: Implementation, instance and specification. The specification document describes what’s required of JVM implementation. Single specification ensures all implementation are interoperable. Implementation program meets the requirements of the JVM specification. JVM Instance is implementation running in process that executes a program compiled into Java bytecode. Thus, the Java machine uses compiler and interpreter too.

2.5 JAVA RUNTIME ENVIROMENT (JRE) Java Runtime Environment is used to provide runtime environment. It is the implementation of JVM. It contains other files and set of libraries that used at runtime by JVM. It is a software package that contains what is required to run a Java program. It includes together Java Class Library Implementation and Java Virtual Machine implementation. The Oracle Corporation, which owns the Java trademark, distributes a Java Runtime environment with their Java Virtual Machine called HotSpot.

2.6 JAVA DEVELOPMENT KIT (JDK) Java Development Kit (JDK) contains JRE and development tools. JDK Tools such as the compilers and debuggers are necessary for developing applications and applets.

Java Libraries in JDK 1.3

Java Development Kit (JDK) contains a Java Class Library for different purposes. Some useful packages in it are mentioned below:

 java.io : to support classes to deal with input & statements.  java.lang : to support classes containing String, Integer,Thread etc.

output Character, Math,

 java.net : to support classes for network related operations and dealing with URL (Uniform Resource Locator)  java.txt : for supporting text elements such as date, times and currency etc.  java.math : to support mathematical functional such roots (integer & decimal both)

as square

 java.applet : to support classes to generate applet – specific environment  java.awt : to support abstract window tool kit and managing GUI (Graphic User Interface)

2.7 RESERVED WORDS Reserved words or keywords are those words which are preserved with the system. These words cannot be applied as a variable name in any program. Java also has reserved words. Some of the reserved/key words are listed below: case do try catch for while

switch break const if else short

int double long new byte public

void import class package static private

default boolean char goto throws float

Comment Statements in Java Programming There are some cases where it becomes difficult for a user to understand the logic applied in a program particularly when any other person has developed it.

In such cases, the programmer keeps mentioning the purpose and action being taken in different steps by applying comment statement in the program. There are three ways to give a comment in Java programming. 1. //

: used for single line comment

2. /* comments to be written */ : used for multi line comment 3. /** documenting comment */

Output Statement in Java Programming System.out.println() and System.out.print() are the statements that are used to get the output of the program or to display messages on the screen. While using System.out.println() statement, the cursor skips the line and passes to the next line after displaying the required result. And, when you use System.out.print() statement, the cursor remains on the same line after displaying the result.

Syntax: System.out.println(“Welcome to Java”); System.out.println(“The product of two numbers is” +a);

Note: The message is to be written within double quotes (“ “) enclosed within braces. When a message is to be displayed along with a variable, then they are to be separated with ‘+’ (plus) sign.

Chapter 3 DATA TYPE AND TOKENS IN JAVA 3.1 DATA TYPES Data types are predefined types of data, which are supported by the programming language. It specifies the size and type of values that can be stored in a variable. In Java Programming we have to deal with various types of data, hence it becomes necessary for a programmer to select an appropriate data type according to the data taken in a program. The data type has been divided into two types: Primitive Type Non-Primitive Type

Primitive Data Types

Primitive data types are pre-defined or built-in data types, which are independent of any other type. For eg. int, long, float, double etc.

Integer Type Integer types can hold whole numbers such as 123 and −96. The values size can depend on stored integer type that we choose. It does not contain decimal point. There are two types of declarations under this heading:

int : applied for short integer number. Bit size -> 32 bits, Format -> int a; a=10; or int a=10; long : applied for large integer number. Bit size -> 64 bits, Format -> long b; b=345678; or long b=345678;

Floating Type Floating point data types are used to represent numbers with a fractional part. There are two types of declarations under this heading: float : applied for small range of decimal values. Bit size -> 32 bits, Format -> float m; m=32.65; or float m=32.65; double : applied for wide range of decimal values. Bit size -> 64 bits, Format -> double n; n=0.0006547839; or n=0.0006547839;

double

Character Type It stores character constants in the memory and contains a single character. A character is enclosed in single quotes (‘ ‘).Strings are enclosed in double quotes(“ “). The character types in Java are as follows:

  Non Numeric Single character

More than one character/a word/a sentence

Character type char

String

Bit Size

Format

16 bits(2 bytes) char c; c=’A’; char d; d=’*’; char c =’A’; More than 16 String a; bits a=”College”;

Boolean Type Boolean data types are used to store values with two states: true or false.

These are non-figurative constants. You can use Boolean type variable to set true or false in order to ensure whether a logical condition is satisfied or not. It assumes one of the values true or false without quotes. For Example: boolean flag=true; or boolean flag=false;

Non-Primitive Data Type

Classes A class, in the context of Java, are templates that are used to create objects, and to define object data types and methods. For Example:

public class MyFirstJavaProgram {  /* This is my first java program. This will print ‘Welcome’ as the output. */  public static void main (String[] args){ System.out.println(“Welcome”); // prints Welcome }

} Let's look at how to save the file, compile, and run the program− Open notepad and add the code as above.

Save the file as: MyFirstJavaProgram.java. Open a command prompt window and go to the directory where you saved the class. Assume it's C:\. Type 'javac MyFirstJavaProgram.java' and press enter to compile your code. If no errors in code then command prompt will process to next line. Then, type ' java MyFirstJavaProgram ' and press enter to run your program. You will be able to see ' Welcome ' printed on the window. We will study later about Arrays in chapter 7

3.2 JAVA TOKENS Each individual character used in a java statement is known as Java Token.

Types of Java Tokens Literals Identifiers Assignments Punctuators Operators

Literals (Constants) These are the constants used in a Java program. Java uses the literals classified in the following ways: Integer Literals : These are the whole numbers having positive or negative values. e.g. 15, 256,etc. Real Literals : They represent numbers with decimal points. e.g. 24.6, 0.0045, etc. Character Literals : The constants which are alphanumeric in nature are called character literals. e.g. ‘A’, ‘b’, ‘1’, ‘*’ etc. String Literals : String is a set of alphanumeric characters. e.g. “Year 2017”, etc.

Identifiers (Variables) Identifiers are also called variables in Java programming. A variable is a named memory location, which contains a value. A variable can be treated by any combination of letters without spaces. We can declare more than one variables of the same type in a statement. Syntax: datatype variable name; e.g. int a; float a,b,c;

Assignments Assignment token assigns the value on its right to the operand on its left. To assign object references operator can also be used. e.g. int speed = 0; int gear = 1;

Punctuators Punctuators are the punctuation signs used in Java. Some punctuators are : ; , ? etc.

Separators These are special characters that are used in Java to separate the characters or variables. e.g. (,),{,},[,] etc.

Operators The operators are the symbols used to perform arithmetical or logical operations in Java programming. e.g. +,-,*,/,||,&&,<,> etc .

Note: We have Detail Explain about Operators in Next Chapter

Chapter 4 OPERATORS AND EXPRESSIONS An operator is basically a symbol or token, which performs logical or arithmetical operations and gives meaningful result. The values which are involved in the operation, are termed as operands. For example :[ a + b * c] where a b and c are operands, + and * are the operators.

4.1 TYPES OF OPERATORS Basically, there are three types of operators in Java which are as follows:

Arithmetical Relational Logical ARITHMETICAL OPERATORS The operators, which are applied to perform arithmetical calculations in a program, are known as arithmetical operators like +,-,*,etc. Arithmetical Expression: An arithmetical expression may contain variables, constants and arithmetical operators together to produce a meaningful result. e.g. a+b,x-10,b*b-4*a*c etc. Arithmetical Statement: If an arithmetical expression is assigned to a variable then it is known as an arithmetical statement. Syntax: Variable = Arithmetical Expression; e.g. x = a + b, z=b*b-4*a*c

Types of Arithmetical Operators Unary Operator Binary Operator Ternary Operator

Unary Operator Unary operator can also be known as arithmetical operator which can be applied with a single operand. e.g. +,-,++ etc.

Unary Increment and Decrement Operators: Unary Increment Operator (++) increases the value of an operand by one whereas Unary Decrement Operator (--) decreases the value of an operand by one. Example: 1. i = i + 1 By applying increment operator it can be written as i++ or ++i 2. j = j – 1 By applying decrement operator it can be written as j-- or --j

Unary Increment/Decrement Operators: Prefix Postfix

Prefix When increment or decrement operators are applied before the operand, it is known as prefix operators. This operator works on the principle ‘CHANGE BEFORE ACTION’. It means the value of the variable changes before the action takes place. Example : p = 5; p = ++p * 4; gives the result 24 as p increases by 1 before the operation performed. p = --p * 4; gives the result 16 as p decreases by 1 before the operation is being performed.

Postfix When increment or decrement operators are applied after the operand, it is known as postfix operators. This operator works on the principle ‘CHANGE AFTER THE ACTION’. It means the value of the variable changes after

performing the operation. Example : p = 5; p = p++ * 4; gives the result 20 as p increases by 1 after the operation performed. p = p-- * 4; gives the result 20 as p decreases by 1 after the operation is being performed.

Binary Arithmetic Operators An arithmetic operator, which deals with two operands is known as Binary Arithmetic Operators. e.g a + b, a – b, etc.

Ternary Operators (Conditional Operator) Ternary Operators takes three operands. It is also called conditional operator because the value assigned to a variable depends upon a logical expression. Syntax: variable = (test expression)? Expression 1:Expression 2; The variable contains the result of expression 1 if the test condition is true otherwise expression 2. e.g. a = 4; b = 2; max = (a>b)? a:b; Here, the condition is true so the output will be 4 as the value of a is 4.

Nested Ternary Operator You can use ternary operator in nested form as shown below : e.g. Program to find maximum among three numbers: int a = 4, b = 10, c = 2; max = (a>b)? (a>c)? a:b

Test condition Expression 1

: (b>c)? b:c;

Expression 2

Since, the test condition is false, it will operate expression 2 which enables value 12 to be stored in max. Hence, max = 12.

RELATIONAL OPERATORS Relational operators compare the values of the variables and return a boolean value in terms of ‘True’ or ‘False’ (i.e. 0 or 1). Java  has six relational operators that are < , > , <= , >= , == , and != .

LOGICAL OPERATORS Java uses logical operators AND(&&), OR(||) or NOT(!). These operators yield 1 or 0 depending upon the output of different expressions . e.g. (a>b)&&(a>c),!(a==b)

Note: If a statement contains all the three logical operators then NOT operator will perform first.

BITWISE OPERATORS Bitwise operators use byte, short, int and long type operands. However, float and double types are not allowed. e.g. & - Bitwise AND | - Bitwise OR ^ - Bitwise XOR << - Left Shift >> - Left Shift

4.2 EXPRESSIONS When you write a program in Java, it is necessary to represent the arithmetical expressions into Java expressions.

Mixed Expression An expression which includes different types of variables or values to yield a result is called as Mixed Expression. e.g. int a; float b; double c; double z = a + b * c; Implicit Type Conversion

In mixed expression, the data type of the result gets converted automatically into its higher type without intervention of the user. This type conversion is known as Implicit Type Conversion. Explicit Type Conversion When the data type gets converted to another type after user intervention, the type conversion is known as Explicit Type Conversion.

e.g. int a, b; float x = (float) (a+b);

Chapter 5 CONDITIONAL AND DECISION MAKING STATEMENTS In the first part of the chapter, we will discuss about unconditional statements, which will help to give a detailed idea of writing Java instructions in a program. In order to perform a specified task in a program you need to provide some values, which can be used during execution of the program. The statement, which accepts the values from the users, is known as input statement. Java provides various ways to use input statements in programming. They are as follows: By assigning the values By using input streams By using Command line arguments

5.1 PROGRAMMING BY USING ASSIGNMENT STATEMENT By using assignment statement, you can take values of data of your own or mentioned in the program. Example: A program in Java to find the sum of two numbers using assignment statement. public class sum { public static void main (String args[]) { int a,b,c; c=0;  

a=15;b=45;

 

c=a+b; System.out.println(“The sum of the two numbers =”+c); }

} Output: The sum of the two numbers = 60.

5.2 PROGRAMMING USING STREAMS Package in Java is basically a collection of classes. Each package includes related built-in functions, which may be used while developing programming logic. Buffer CPU or processor is the fastest device in a computer. Other peripheral devices are comparatively slower then processor. Due to speed differences it becomes difficult to have data communication between processor and peripheral devices. Hence, a high speed memory is applied between I/O devices and processor used as a bridge to synchronize their speeds. This high-speed temporary storage (cache memory) is termed as Buffer. You need to activate the buffer before any input/output operation.

Activating Buffer in Java InputStreamReader