Unit-1_OOPJ.pdf

OOPJ Unit-1 Created By Chavda Dharmendra  Java Introduction What is Java? - Java is a popular high-level, object-oriented programming language, which was originally developed by Sun Microsystems and released in 1...

OOPJ Unit-1 Created By Chavda Dharmendra  Java Introduction What is Java? - Java is a popular high-level, object-oriented programming language, which was originally developed by Sun Microsystems and released in 1995. - Currently, Java is owned by Oracle and more than 3 billion devices run Java. - Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX. - Today Java is being used to develop numerous types of software applications including Desktop Apps, Mobile apps, Web apps, Games, and much more. Java Example Let's have a quick look at Java programming example. Simple.java 1. class Test{ 2. public static void main(String args[]){ 3. System.out.println("Hello Java"); 4. } 5. } File -> Save -> d:\Test.java Compiling the program - To compile the program, we must run the Java compiler (javac), with the name of the source file on “command prompt” like as follows - If everything is OK, the “javac” compiler creates a file called “Test.class” containing byte code of the program. Running the program - We need to use the Java Interpreter to run a program (Java Test). Application - According to Sun, 3 billion devices run Java. - There are many devices where Java is currently used. - Some of them are as follows: 1. Desktop Applications such as acrobat reader, media player, antivirus, etc. 2. Web Applications such as irctc.co.in, javatpoint.com, etc. 3. Enterprise Applications such as banking applications. 4. Mobile 5. Embedded System 6. Smart Card 7. Robotics 8. Games, etc. Types of Java Applications - There are mainly 4 types of applications that can be created using Java programming: 1) Standalone Application - Standalone applications are also known as desktop applications or window-based applications. - These are traditional software that we need to install on every machine. - Examples of standalone application are Media player, antivirus, etc. AWT and Swing are used in Java for creating standalone applications. 2) Web Application - An application that runs on the server side and creates a dynamic page is called a web application. - Currently, Servlet, JSP, Struts, Spring, Hibernate, JSF(Javaserver Faces), etc. technologies are used for creating web applications in Java. 3) Enterprise Application - An application that is distributed in nature, such as banking applications, etc. is called an enterprise application. - It has advantages like high-level security, load balancing, and clustering. In Java, EJB(Enterprise java beans) is used for creating enterprise applications. 4) Mobile Application - An application which is created for mobile devices is called a mobile application. - Currently, Android and Java ME(Micro Edition) are used for creating mobile applications. History of Java - Java was originally designed for interactive television, but it was too advanced technology for the digital cable television industry at the time. - Java team members (also known as Green Team), initiated this project to develop a language for digital devices such as set-top boxes, televisions, etc. - Java was developed by James Gosling, who is known as the father of Java, in 1995. - Currently, Java is used in internet programming, mobile devices, games, e-business solutions, etc. Following are given significant points that describe the history of Java. 1) James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. The small team of sun engineers called Green Team. 2) Initially it was designed for small, embedded systems in electronic appliances like set-top boxes. 3) Firstly, it was called "Greentalk" by James Gosling, and the file extension was.gt. 4) After that, it was called Oak and was developed as a part of the Green project. Why Java was named as "Oak"? 5) Why Oak? Oak is a symbol of strength and chosen as a national tree of many countries like the U.S.A., France, Germany, Romania, etc. 6) In 1995, Oak was renamed as "Java" because it was already a trademark by Oak Technologies. Why Java Programming named "Java"? 7) Why had they chose the name Java for Java language? - The team gathered to choose a new name. The suggested words were "dynamic", "revolutionary", "Silk", "jolt", "DNA", etc. - They wanted something that reflected the essence of the technology: revolutionary, dynamic, lively, cool, unique, and easy to spell, and fun to say. - According to James Gosling, "Java was one of the top choices along with Silk". - Since Java was so unique, most of the team members preferred Java than other names. 8) Java is an island in Indonesia where the first coffee was produced (called Java coffee). James Gosling while having a cup of coffee nearby his office chose Java name. 9) Notice that Java is just a name, not an acronym. 10) Initially developed by James Gosling at Sun Microsystems (which is now a subsidiary of Oracle Corporation) and released in 1995. 11) JDK 1.0 was released on January 23, 1996. Features of Java The features of Java are also known as Java buzzwords. A list of the most important features of the Java language is given below. 1. Simple 2. Object-Oriented 3. Portable 4. Platform independent 5. Secured 6. Robust 7. Architecture neutral 8. Interpreted 9. High Performance 10. Multithreaded 11. Distributed 12. Dynamic Simple Java is very easy to learn, and its syntax is simple, clean and easy to understand. According to Sun Microsystem, Java language is a simple programming language because: o Java syntax is based on C++ (so easier for programmers to learn it after C++). o Java has removed many complicated and rarely-used features, for example, explicit pointers, operator overloading, etc. o There is no need to remove unreferenced objects because there is an Automatic Garbage Collection in Java. Object-oriented - Java is an object-oriented programming language. - Everything in Java is an object. - Object-oriented means we organize our software as a combination of different types of objects that incorporate both data and behaviour. - Object-oriented programming (OOPs) is a methodology that simplifies software development and maintenance by providing some rules. Basic concepts of OOPs are: 1. Object 2. Class 3. Inheritance 4. Polymorphism 5. Abstraction 6. Encapsulation Platform Independent - Java code can be executed on multiple platforms, for example, Windows, Linux, Sun Solaris, Mac/OS, etc. - Java code is compiled by the compiler and converted into bytecode. - This bytecode is a platform-independent code because it can be run on multiple platforms, - i.e., Write Once and Run Anywhere (WORA). Secured - Java is best known for its security. With Java, we can develop virus-free systems. Java is secured because: - No explicit pointer - Java Programs run inside a virtual machine sandbox - Classloader: Classloader in Java is a part of the Java Runtime Environment (JRE) which is used to load Java classes into the Java Virtual Machine dynamically. - Bytecode Verifier: It checks the code fragments for illegal code that can violate access rights to objects. - Security Manager: It determines what resources a class can access such as reading and writing to the local disk. Robust - The English mining of Robust is strong. Java is robust because: - It uses strong memory management. - There is a lack of pointers that avoids security problems. - Java provides automatic garbage collection which runs on the Java Virtual Machine to get rid of objects which are not being used by a Java application anymore. - There are exception handling and the type checking mechanism in Java. All these points make Java robust. Architecture-neutral - Java is architecture neutral because there are no implementation dependent features, - for example, the size of primitive types is fixed. - In C programming, int data type occupies 2 bytes of memory for 32-bit architecture and 4 bytes of memory for 64-bit architecture. - However, it occupies 4 bytes of memory for both 32 and 64-bit architectures in Java. Interpreted - Java is a platform independent programming language - It means that we can run java on platform that have a java interpreter. - To convert the byte code into machine code we deploy the.class file on the JVM. - The JVM converts that code into machine code using the java interpreter. - The compiler compiles the source code into the java bytecode. - In the same way, the java interpreter converts or translates the bytecode into the machine code. - After that the machine code interacts with the operating system. Portable - Java is portable because it facilitates you to carry the Java bytecode to any platform. - It doesn't require any implementation. High-performance - Java is faster than other traditional interpreted programming languages because Java bytecode is "close" to native code. - It is still a little bit slower than a compiled language (e.g., C++). - Java is an interpreted language that is why it is slower than compiled languages, e.g., C, C++, etc. Distributed - Java is distributed because it facilitates users to create distributed applications in Java. - RMI and EJB are used for creating distributed applications. - This feature of Java makes us able to access files by calling the methods from any machine on the internet. Multi-threaded - A thread is like a separate program, executing concurrently. - We can write Java programs that deal with many tasks at once by defining multiple threads. - The main advantage of multi-threading is that it doesn't occupy memory for each thread. - It shares a common memory area. - Threads are important for multi-media, Web applications, etc. Dynamic - Java is a dynamic language. - It supports the dynamic loading of classes. - It means classes are loaded on demand. - It also supports functions from its native languages, i.e., C and C++. - Java supports dynamic compilation and automatic memory management (garbage collection).  Using data within java program Constants - A constant is a variable whose value cannot change once it has been assigned. Java doesn't have built-in support for constants. - A constant can make our program more easily read and understood by others. - In addition, a constant is cached by the JVM as well as our application, so using a constant can improve performance. - To define a variable as a constant, we just need to add the keyword "final" in front of the variable declaration. Syntax final float pi = 3.14f; - The above statement declares the float variable "pi" as a constant with a value of 3.14f. - We cannot change the value of "pi" at any point in time in the program. - Later if we try to do that by using a statement like "pi=5.25f", Java will throw errors at compile time itself. - It is not mandatory that we need to assign values of constants during initialization itself. Literals in Java - In Java, literal is a notation that represents a fixed value in the source code. - In lexical analysis, literals of a given type are generally known as tokens. Literals - In Java, literals are the constant values that appear directly in the program. - It can be assigned directly to a variable. Java has various types of literals. The following figure represents a literal. Types of Literals in Java There are the majorly four types of literals in Java: 1. Integer Literal 2. Character Literal 3. Boolean Literal 4. String Literal Integer Literals Integer literals are sequences of digits. There are three types of integer literals: o Decimal Integer: - These are the set of numbers that consist of digits from 0 to 9. - It may have a positive (+) or negative (-) Note that between numbers commas and non-digit characters are not permitted. - For example, 5678, +657, -89, etc. - int decVal = 26; o Octal Integer: - It is a combination of number have digits from 0 to 7 with a leading 0. - For example, 045, 026, - int octVal = 067; o Hexa-Decimal: - The sequence of digits preceded by 0x or 0X is considered as hexadecimal integers. - It may also include a character from a to f or A to F that represents numbers from 10 to 15, respectively. - For example, 0xd, 0xf, - int hexVal = 0x1a; o Binary Integer: - Base 2, whose digits consists of the numbers 0 and 1 (you can create binary literals in Java SE 7 and later). - Prefix 0b represents the Binary system. - For example, 0b11010. - int binVal = 0b11010; Backslash Literals - Java supports some special backslash character literals known as backslash literals. They are used in formatted output. For example: \n: It is used for a new line \t: It is used for horizontal tab \b: It is used for blank space \v: It is used for vertical tab \a: It is used for a small beep \r: It is used for carriage return \': It is used for a single quote \": It is used for double quotes Character Literals - A character literal is expressed as a character or an escape sequence, enclosed in a single quote ('') mark. It is always a type of char. - For example, 'a', '%', '\u000d', etc. String Literals - String literal is a sequence of characters that is enclosed between double quotes ("") marks. - It may be alphabet, numbers, special characters, blank space, etc. - For example, "Jack", "12345", "\n", etc. Floating Point Literals - The vales that contain decimal are floating literals. - In Java, float and double primitive types fall into floating-point literals. Keep in mind while dealing with floating-point literals. o Floating-point literals for float type end with F or f. For example, 6f, 8.354F, etc. It is a 32-bit float literal. o Floating-point literals for double type end with D or d. It is optional to write D or d. For example, 6d, 8.354D, etc. It is a 64-bit double literal. o It can also be represented in the form of the exponent. Floating: 1. float length = 155.4f; Decimal: 1. double interest = 99658.445; Decimal in Exponent form: 1. double val= 1.234e2; Boolean Literals - Boolean literals are the value that is either true or false. - It may also have values 0 and 1. - For example, true, 0, etc. 1. boolean isEven = true; Null Literals - Null literal is often used in programs as a marker to indicate that reference type object is unavailable. - The value null may be assigned to any variable, except variables of primitive types. 1. String stuName = null; 2. Student age = null; Java Variables - A variable is a container which holds the value while the Java program is executed. - A variable is assigned with a data type. - Variable is a name of memory location. - There are three types of variables in java: local, instance and static. - There are two types of data types in Java: primitive and non-primitive. 1. int data=50;//Here data is variable Types of Variables There are three types of variables in Java: o local variable o instance variable o static variable 1) Local Variable - Sometimes to meet temporary requirements of the programmers. We can declare variables inside a method or block or constructor such type of variable are called Local variable or temporary variable or stack variable. - You can use this variable only within that method and the other methods in the class aren't even aware that the variable exists. - A local variable cannot be defined with "static" keyword. - Local variable will be stored inside stack memory. 2) Instance Variable - A variable declared inside the class but outside the body of the method, is called an instance variable. It is not declared as static. - We can’t access instance variable directly from static area but we can access by using object reference. - It is called an instance variable because its value is instance-specific and is not shared among instances. - Instance variable will be stored in the Heap memory at part of object. 3) Static variable - A variable that is declared as static is called a static variable. It cannot be local. - Static variable should be declare within the class directly but outside of any method or block of constructor. - We can access static variable either by object reference or by class name but recommended to use class name. - Memory allocation for static variables happens only once when the class is loaded in the memory. - Static variable will be stored in Method area. Example to understand the types of variables in java 1. public class A 2. { 3. static int m=100;//static variable 4. void method() 5. { 6. int n=90;//local variable 7. } 8. public static void main(String args[]) 9. { 10. int data=50;//instance variable 11. } 12. }//end of class Data Types in Java - Data types specify the different sizes and values that can be stored in the variable. There are two types of data types in Java: 1. Primitive data types: The primitive data types include boolean, char, byte, short, int, long, float and double. 2. Non-primitive data types: The non-primitive data types include Classes,String, Interfaces, and Arrays. There are 8 types of primitive data types: o boolean data type o byte data type o char data type o short data type o int data type o long data type o float data type o double data type  Data Type Default Value Default size boolean false 1 bit Char '\u0000' 2 byte Byte 0 1 byte Short 0 2 byte Int 0 4 byte Long 0L 8 byte Float 0.0f 4 byte Double 0.0d 8 byte Boolean Data Type - The Boolean data type is used to store only two possible values: true and false. - This data type is used for simple flags that track true/false conditions. The Boolean data type specifies one bit of information, but its "size" can't be defined precisely. Example: 1. Boolean one = false Byte Data Type - The byte data type is an example of primitive data type. - It is an 8-bit signed two's complement integer. - Its value-range lies between -128 to 127 (inclusive). - Its minimum value is -128 and maximum value is 127. - Its default value is 0. - The byte data type is used to save memory in large arrays where the memory savings is most required. - It saves space because a byte is 4 times smaller than an integer. - It can also be used in place of "int" data type. Example: 1. byte a = 10, byte b = -20 Short Data Type - The short data type is a 16-bit signed two's complement integer. - Its value-range lies between -32,768 to 32,767 (inclusive). - Its minimum value is -32,768 and maximum value is 32,767. Its default value is 0. - The short data type can also be used to save memory just like byte data type. - A short data type is 2 times smaller than an integer. Example: 1. short s = 10000, short r = -5000 Int Data Type - The int data type is a 32-bit signed two's complement integer. - Its value-range lies between - 2,147,483,648 (-2^31) to 2,147,483,647 (2^31 -1) (inclusive). - Its minimum value is - 2,147,483,648and maximum value is 2,147,483,647. - Its default value is 0. The int data type is generally used as a default data type for integral values unless if there is no problem about memory. Example: 1. int a = 100000, int b = -200000 Long Data Type - The long data type is a 64-bit two's complement integer. - Its value-range lies between -9,223,372,036,854,775,808(-2^63) to 9,223,372,036,854,775,807(2^63 - 1)(inclusive). - Its minimum value is - 9,223,372,036,854,775,808and maximum value is 9,223,372,036,854,775,807. Its default value is 0. The long data type is used when you need a range of values more than those provided by int. Example: 1. long a = 100000L, long b = -200000L Float Data Type - The float data type is a single-precision 32-bit IEEE 754 floating point. - -3.4e38 to 3.4e38 - It is recommended to use a float (instead of double) if you need to save memory in large arrays of floating point numbers. The float data type should never be used for precise values, such as currency. Its default value is 0.0F. Example: 1. float f1 = 234.5f Double Data Type - The double data type is a double-precision 64-bit IEEE 754 floating point. - -1.7r308 to 1.7e308 - The double data type is generally used for decimal values just like float. - The double data type also should never be used for precise values, such as currency. Its default value is 0.0d. Example: 1. double d1 = 12.3 Char Data Type - The char data type is a single 16-bit Unicode character. - Its value-range lies between '\u0000' (or 0) to '\uffff' (or 65,535 inclusive). - The char data type is used to store characters. Example: 1. char letterA = 'A'  Understanding numeric, Type Conversion - In Java, type casting is a method or process that converts a data type into another data type in both ways manually and automatically. - The compiler and manual conversion performed by the programmer do the automatic conversion. - Numeric type conversion in Java is an essential concept, particularly when dealing with different numeric data types. - Java provides both implicit and explicit ways to convert between these types. Numeric Data Types in Java 1. byte: 8-bit integer 2. short: 16-bit integer 3. int: 32-bit integer 4. long: 64-bit integer 5. float: 32-bit floating-point 6. double: 64-bit floating-point Implicit Conversion (Widening Conversion) - Converting a lower data type into a higher one is called implicit conversion type casting. - It is also known as widening or casting down. - It is done automatically. - It is safe because there is no chance to lose data. - Implicit conversions happen automatically when converting a smaller type to a larger type (widening conversion). - This is safe and doesn’t result in data loss.  byte -> short -> int -> long -> float -> double Example: public class Main { public static void main(String[] args) { int a = 100; double b = a; // int to double conversion System.out.println("int value: " + a); // 100 System.out.println("double value: " + b); // 100.0 } } Explicit Conversion (Narrowing Conversion) - Converting a higher data type into a lower one is called explicit conversion type casting. - It is also known as narrowing or casting up. - It is done manually by the programmer. ] - If we do not perform casting then the compiler reports a compile-time error. - To perform explicit conversion, you use the cast operator (type).  double -> float -> long -> int -> short -> byte Example: public class Main { public static void main(String[] args) { double a = 100.04; int b = (int) a; // explicit conversion from double to int System.out.println("double value: " + a); // 100.04 System.out.println("int value: " + b); // 100 (fractional part is truncated) } } Type Conversion Methods - Java provides wrapper classes for each of the primitive types (e.g., Integer, `Double`) that include methods for converting strings to numeric types and vice versa. - String to int: String str = "123"; int num = Integer.parseInt(str); - String to double: String str = "123.45"; double num = Double.parseDouble(str); - int to String: int num = 123; String str = Integer.toString(num); - double to String: double num = 123.45; String str = Double.toString(num); Considerations 1. Precision Loss: Converting from a higher precision type (e.g., `double`) to a lower precision type (e.g., `int`) can result in loss of data. 2. Range Overflow: If the value being converted exceeds the range of the target type, it will result in an overflow and unexpected results. Example of Range Overflow: public class Main { public static void main(String[] args) { int a = 130; byte b = (byte) a; // range of byte is -128 to 127 System.out.println("int value: " + a); // 130 System.out.println("byte value: " + b); // -126 (overflow occurred) } } - Understanding numeric type conversion in Java is vital for effective and error-free programming. - It involves implicit conversions (widening) that occur automatically and explicit conversions (narrowing) that must be done manually with care. - Using wrapper classes for conversions between strings and numeric types can also be very useful. Operators in Java - Operator in Java is a symbol that is used to perform operations. - For example: +, -, *, / etc. There are many types of operators in Java which are given below:  Unary Operator,  Arithmetic Operator,  Shift Operator,  Relational Operator,  Bitwise Operator,  Logical Operator,  Ternary Operator and  Assignment Operator. Java Operator Precedence Operator Type Category Precedence Unary postfix expr++ expr-- prefix ++expr --expr +expr -expr ~ ! Arithmetic multiplicative */% additive +- Shift shift > >>> Relational comparison < > = instanceof equality == != Bitwise bitwise AND & bitwise exclusive OR ^ bitwise inclusive OR | Logical logical AND && logical OR || Ternary ternary ?: Assignment assignment = += -= *= /= %= &= ^= |= = >>>= Java Unary Operator - The Java unary operators require only one operand. - Unary operators are used to perform various operations i.e.  incrementing/decrementing a value by one  negating an expression  inverting the value of a Boolean Java Unary Operator Example: ++ and -- 1. public class OperatorExample{ 2. public static void main(String args[]){ 3. int x=10; 4. System.out.println(x++);//10 (11) 5. System.out.println(++x);//12 6. System.out.println(x--);//12 (11) 7. System.out.println(--x);//10 8. }} Output: 10 12 12 10 Java Unary Operator Example 2: ++ and -- 1. public class OperatorExample{ 2. public static void main(String args[]){ 3. int a=10; 4. int b=10; 5. System.out.println(a++ + ++a);//10+12=22 6. System.out.println(b++ + b++);//10+11=21 7. 8. }} Output: 22 21 Java Unary Operator Example: ~ and ! 1. public class OperatorExample{ 2. public static void main(String args[]){ 3. int a=10; 4. int b=-10; 5. boolean c=true; 6. boolean d=false; 7. System.out.println(~a);//-11 (minus of total positive value which starts from 0) 8. System.out.println(~b);//9 (positive of total minus, positive starts from 0) 9. System.out.println(!c);//false (opposite of boolean value) 10. System.out.println(!d);//true 11. }} Output: -11 9 false true Java Arithmetic Operators - Java arithmetic operators are used to perform addition, subtraction, multiplication, and division. - They act as basic mathematical operations. Java Arithmetic Operator Example 1. public class OperatorExample{ 2. public static void main(String args[]){ 3. int a=10; 4. int b=5; 5. System.out.println(a+b);//15 6. System.out.println(a-b);//5 7. System.out.println(a*b);//50 8. System.out.println(a/b);//2 9. System.out.println(a%b);//0 10. }} Output: 15 5 50 2 0 Java Arithmetic Operator Example: Expression 1. public class OperatorExample{ 2. public static void main(String args[]){ 3. System.out.println(10*10/5+3-1*4/2); 4. }} Output: 21 Java Left Shift Operator - The Java left shift operator > vs >>> 1. public class OperatorExample{ 2. public static void main(String args[]){ 3. //For positive number, >> and >>> works same 4. System.out.println(20>>2); 5. System.out.println(20>>>2); 6. //For negative number, >>> changes parity bit (MSB(most significant bit.) to 0 7. System.out.println(-20>>2); 8. System.out.println(-20>>>2); 9. }} Output: 5 5 -5 1073741819 Java AND Operator Example: Logical && and Bitwise & - The logical && operator doesn't check the second condition if the first condition is false. - It checks the second condition only if the first one is true. - The bitwise & operator always checks both conditions whether first condition is true or false. 1. public class OperatorExample{ 2. public static void main(String args[]){ 3. int a=10; 4. int b=5; 5. int c=20; 6. System.out.println(a