![ public class Test {
public static void main(String args[]) {
Integer x = 5; // boxes int to an Integer object
x = x + 10; // unboxes the Integer to a int
System.out.println(x);
}
}
Output
15
When x is assigned an integer value, the compiler boxes the integer because x is
integer object. Later, x is unboxed so that they can be added as an integer.](https://image.slidesharecdn.com/javaintroduction-180309092439/85/Java-introduction-24-320.jpg)
![1.public class WrapperExample1{
2.public static void main(String args[]){
3.//Converting int into Integer
4.int a=20;
5.Integer i=Integer.valueOf(a);//converting int
into Integer
6.Integer j=a;//autoboxing, now compiler will
write Integer.valueOf(a) internally
7.
8.System.out.println(a+" "+i+" "+j);
9.}}](https://image.slidesharecdn.com/javaintroduction-180309092439/85/Java-introduction-25-320.jpg)
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Java introduction
- 2. What is Java? Java is a programming language and a platform. Java is a high level, robust, secured and object- oriented programming language. Platform: Any hardware or software environment in which a program runs, is known as a platform. Since Java has its own runtime environment (JRE) and API, it is called platform.
- 3. Where it is used? Desktop Applications such as acrobat reader, media player, antivirus etc. Web Applications such as irctc.co.in, javatpoint.com etc. Enterprise Applications such as banking applications. Mobile Embedded System Smart Card Robotics Games etc.
- 4. Types of Java Applications 1) Standalone Application It is also known as desktop application or window-based application. An application that we need to install on every machine such as media player, antivirus etc. AWT and Swing are used in java for creating standalone applications.
- 5. 2) Web Application An application that runs on the server side and creates dynamic page, is called web application. Currently, servlet, jsp. technologies are used for creating web applications in java. 3) Enterprise Application An application that is distributed in nature, such as banking applications etc. It has the advantage of high level security, load balancing and clustering. In java, EJB is used for creating enterprise applications.
- 6. 4) Mobile Application An application that is created for mobile devices. Currently Android and Java ME are used for creating mobile applications.
- 7. History of Java Java history is interesting to know. The history of java starts from Green Team. Java team members (also known as Green Team), initiated a revolutionary task to develop a language for digital devices such as set-top boxes, televisions etc. Java is used in internet programming, mobile devices, games, e-business solutions etc.
- 8. Firstly, it was called "Greentalk" by James Gosling and file extension was .gt. After that, it was called Oak and was developed as a part of the Green project. Why Oak? Oak is a symbol of strength and choosen as a national tree of many countries like U.S.A., France, Germany, Romania etc. In 1995, Oak was renamed as "Java" because it was already a trademark by Oak Technologies.
- 9. Java is an island of Indonesia where first coffee was produced (called java coffee). Notice that Java is just a name not an acronym. Originally developed by James Gosling at Sun Microsystems (which is now a subsidiary of Oracle Corporation) and released in 1995. In 1995, Time magazine called Java one of the Ten Best Products of 1995. JDK 1.0 released in(January 23, 1996).
- 11. Simple Java language is simple because: syntax is based on C++ (so easier for programmers to learn it after C++). removed many confusing and/or rarely-used features e.g., explicit pointers, operator overloading etc. No need to remove unreferenced objects because there is Automatic Garbage Collection in java.
- 12. Object-oriented Object Class Inheritance Polymorphism Abstraction Encapsulation
- 13. Platform Independent There are two types of platforms software-based and hardware-based. Java provides software-based platform. it is a software-based platform that runs on the top of other hardware-based platforms. 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).
- 15. Secured
- 16. Java is secured because: o No explicit pointer o Java Programs run inside virtual machine . o Classloader: adds security by separating the package for the classes of the local file system from those that are imported from network sources.
- 17. Bytecode Verifier: checks the code fragments for illegal code that can violate access right to objects. Security Manager: determines what resources a class can access such as reading and writing to the local disk. These security are provided by java language.
- 18. Robust Robust simply means strong. Java uses strong memory management. There are lack of pointers that avoids security problem. There is automatic garbage collection in java. There is exception handling and type checking mechanism in java. All these points makes java robust.
- 19. Architecture-neutral There is no implementation dependent features e.g. 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. But in java, it occupies 4 bytes of memory for both 32 and 64 bit architectures.
- 20. Portable We may carry the java bytecode to any platform. High-performance Java is faster than traditional interpretation since byte code is "close" to native code still somewhat slower than a compiled language (e.g., C++)
- 21. Distributed We can create distributed applications in java. RMI and EJB are used for creating distributed applications. We may access files by calling the methods from any machine on the internet.
- 22. Wrapper classes The object of the wrapper class contains or wraps its respective primitive data type. Converting primitive data types into object is called boxing, and this is taken care by the compiler.
- 23. Primitive Type Wrapper class boolean Boolean char Character byte Byte short Short int Integer long Long float Float double Double
- 24. public class Test { public static void main(String args[]) { Integer x = 5; // boxes int to an Integer object x = x + 10; // unboxes the Integer to a int System.out.println(x); } } Output 15 When x is assigned an integer value, the compiler boxes the integer because x is integer object. Later, x is unboxed so that they can be added as an integer.
- 25. 1.public class WrapperExample1{ 2.public static void main(String args[]){ 3.//Converting int into Integer 4.int a=20; 5.Integer i=Integer.valueOf(a);//converting int into Integer 6.Integer j=a;//autoboxing, now compiler will write Integer.valueOf(a) internally 7. 8.System.out.println(a+" "+i+" "+j); 9.}}