In this particular Markdown, we have further updates regarding the left one concepts of Basics of Java which are important for Beginners, together by having the Codes and the main Markdown file of Basic Java regarding the code integrated Concepts.
- Java as OOPs
- History of Java
- Difference of Java and C++
- Java Architecture
When we talk about OOPs, not just in Java in other programming language also we starts using Objects in Programming in order to implement them as Primary source to create something with the code. As the objects are seen by the user in order to perform different tasks.
OOPs usually aims for the implementation of real world Objects in Programming like Inheritance, Data Hiding, Polymorphism,..etc Also the main aim is to bind the Data and the functions (Operates on Object/Data) so that not any other part can access the Data.
Access Modifiers : The Access regarding usage outside and inside the class over to its member is been defined or modified using these access modifiers.
Class : We can consider it as a Blueprint or Prototype with the help of which the Objects are created. It is used in order to represent a particular set of members and methods to one or more objects. It reduces the redudancy of code with the help of using a particular class multiple times in order to create multiple objects of it.
Objects : It is to be considered as a Basic Unit of OOPs which is used to represent the Real-Life Entities. A General Java program is been implemented with different kinds of Objects. And these are the part of the code visible to the users or viewers.
- Developed by - James Gosling in 1990
- Project was called as GreenTalk regarding development of JAVA
- Further it was named as OA
| Java | C++ |
|---|---|
| Regarding Memory Management it supports Threads,References and Interface, also don't supports Pointers | Regarding Memory Management it uses Pointers,Structures and Unions |
| Have Wide-Range of Libraries or Classes regarding different High-Level of Services | As per comparison have Low-Level of Functionality |
| Supports Inheritance but in case of Multiple uses Interfaces | Supports both Single and Multiple Inheritance |
| Don't supports Operator Overloading | Supports Operator Overloading |
| For Handling Programs, functions and variables resides inside the classes and packages only | Regarding this feature functions and variables reside outside the classes |
| It is Platform-Independent as the generated Byte-Code runs on every OS | It is Platform-Dependent and the code needs to recompiled for running on different OS |
| It supports Threads and Concept of Multi-Threading | Don't have Built-in feature for Threads and is dependent on Libraries |
JVM acts or works like a run-time engine for running JVM Applications. It is reponsible for the calling of the main method present in the Java Code for its execution, and further its is a Part of JRE (Java-Runtime Environment). We can used the WORA (Write Once Run Anywhere) property of Java only because of JVM.
When a Java File with .java extension is been compiled, then a .class is been generated by the JIT (Just In Time) Compiler. For running the code, this .class file is been passed through various purpose.
It includes 3 properties or functions further process as mentioned below :-
- Loading -> Firstly, the loader reads the .class file and generates its Binary Code together by saving it into the Method Area. For each .class file JVM stores (i) Fully Qualified Name of Loaded Class, (ii) Class, Enum or Inteface if available together by its properties like methods, members,..etc
It also creates an Object of type class to represent the file in Heap Memory.
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Linking -> Performs Verification, Preparation and sometimes Resolutions. Verification is the process in which we get the ensurity of the Correctness of the .class file, whether its is properly formatted or not and this verification is done by ByteCodeVerifier. In case of Preparation, the JVM allocates memory for class static variable and initialize it the default values. In Resolution, the replacement of Symbolic Reference to Direct Reference is done by searching in the Methods Area to locate referenced entity.
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Initialization -> In this process, the static variables with static keywords are assigned their required values as per defined in the code, also it is done from top to bottom in case of Classes and from Parent to Child in case of Hierarchy.
We also have following Loaders in Initialization Phase :-
It is mainly used for interaction with the Native Method's Libraries and also provides native libraries(C/C++) required for the execution. It helps/enables JVM to call C/C++ Libraries and to be called by C/C++ Libraries which may be Hardware Dependent.
Execution engine executes the “.class” (bytecode). It reads the byte-code line by line, uses data and information present in various memory area and executes instructions. It can be classified into three parts:
- Interpreter : It interprets the bytecode line by line and then executes. The disadvantage here is that when one method is called multiple times, every time interpretation is required.
- Just-In-Time Compiler(JIT) : It is used to increase the efficiency of an interpreter. It compiles the entire bytecode and changes it to native code so whenever the interpreter sees repeated method calls, JIT provides direct native code for that part so re-interpretation is not required, thus efficiency is improved.
- Garbage Collector: It destroys un-referenced objects. For more on Garbage Collector, refer Garbage Collector.
- Method Area ->> In this all the properties of a Class together by the static variables are stored, also each JVM have only one Method Area together by being a shared resource.
- Heap Area ->> All information regarding Object is included in it, and is only one for each JVM being a shared resources.
- Stack Area ->> Run-time Stack is created for each thread by JVM. Its area is called as Activation Record or Stack Frame, when a thread is terminated its stack area is destroyed and it is not sharable resource.
- PC Registers ->> Used to store address of current execution of thread and is provided seperately to each thread.
- Native Method Stack ->> It is provided each to each thread and is created for storing Native Information regarding that thread.