Java is a platform independent, case sensitive language which is used to create secure and robust applications. It was developed by James Gosling in 1991. Apart from having a C like notation, it was much easier, uniform and simple than C/C++. The first version of Java was released by Sun Microsystems in 1995. It works on a "Write Once Run Anywhere" platform. Java is open source software. The J2 versions of Java were renamed as Java SE, Java EE, and Java ME. Java is an object-oriented programming language. Java is a combination of the features of C and C++. It has inherited its features from C and object-oriented programming feature from C++.
In order to load the Java Classes into a virtual environment, Classloader are used. A class loader will load key classes such as java.lang.object and several other codes into the memory. Usually, these classes are loaded only if a demand occurs. Since Java Runtime Environment includes loaders, they need not know about file and file systems. Also, the loaders are responsible for converting the named class into an equivalent binary form.
Call by value:
A process in which the values of the actual parameters sent by the calling function are copied to the formal parameters of the called function.
Call by reference:
A process in which the parameters of a calling function are passed to the parameters of the called function using an address.
Java virtual machine is actually an abstract machine which provides a runtime environment in which the java bytecode gets executed. A JVM performs some main tasks such as- loading, verifying and executing the code. It also provides a runtime environment.
The Java runtime environment is used to provide a runtime environment. It is implemented by JVM. It consists of certain libraries which are used by JVM at runtime.
The Java development kit consists of JRE and all the development tools which are necessary for compiling a program.
The major features of Java are listed below: –
Overriding concept in java means when there are two methods with the same signature, one is in the parent class and the other one is in the child class. The override annotation can be used in the child class overridden method.
Java use garbage collection which is performed automatically in Java to free the memory space from unused objects automatically. It is used to identify and dispose those objects that are no longer needed for the application. In other languages like C and C++ you must perform garbage collection by yourself to manage the memory, it means Java provides good memory management.
We do expectation handling to handle the errors or problems that arise due to the syntax error or logical error. If these errors are not handled properly then it disturbs the flow of the application and performs abnormal behavior like stops the application.so, these errors need to be handled carefully for smooth and error-free flow.
There are 2 types of exceptions.
When we have to store a collection of objects which is unordered we prefer the Set interface. The other main reason for using Set is we can ignore duplicate entities and keep our data unique. For example, if we have a Set containing different entities "John", "Smith", "Smith", "John", "Alisha". It will display "John" and "Smith" only one time in output by ignoring the duplicated entities. On the other hand, List is and ordered the collection of objects. So, when we have to keep our entities in ordered form while not caring about the duplication we will prefer List.
The purpose of the final keyword is to make things unchanged in application lifeline. We can make a class, method or variable unchanged by writing "final" keyword before the method, class, and variable. When the final is written before the variable, it remains unchanged (you can’t change it). A function which use final keyword cannot be overridden. On the other hand, if we make a class final we cannot extend it. When we have to make these unchanged conditions, we prefer to use the final keyword.
The process of the connecting function call with function body is called binding. When this binding is done at compile time, it is called early binding. Early binding is static binding it is done when the type of an object is determined at compile time. On the hand, late binding is done at runtime. Late binding is dynamic binding because it is done at runtime by the compiler itself.
The purpose of using multithreading is to make multiple lightweight processes running simultaneously because threads have a plus point, they are lightweight process. Multiple processes not only reserve the memory space but also make the increase the work complication as well. To eliminate the memory space issue and complications we prefer multithreading because they used a shared memory area which saves memory and performs better memory management.
Thread scheduler maintains threading states by using primitive and time slicing scheduling. It schedules the tasks by setting priority and time. Only one thread can run at a time in a single process by thread scheduler. When the highest priority is set to a process, the first process at highest priority gets starts before coming into dead or waiting state, after that the next process in the waiting state comes and make it task done and so on. This is how the thread scheduler schedules the task.
Deadlock is a situation that occurs when the same resource is required by two processes. This situation occurs in multithreading when one thread holds a resource which is required by the second thread and second thread holds a resource which is required by the first thread. To identify the deadlock, we can use the jConsole/VisualVM, it will show exactly which threads are getting locked and on which object.
It is not possible in java to write the definition of a function inside another function. It is like we are creating confusion for the compiler in making a decision for which function definition part to terminate and which is not. It is not recommended and not professional. For this purpose, we can use Lambda expression.
Note: Lambda expression is introduced in Java 8 which can be created without belonging to any class.
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Java object-oriented programming paradigm is far different from C++ and other languages. There was a...