What Is Abstract Machine In Java

Although abstract classes cannot be used to instantiate objects they can be used to create object references because javas approach to run time polymorphism is implemented through the use of super class references.

What is abstract machine in java. The abstract keyword is a non access modifier used for classes and methods. To implement an abstract class in java we need to follow the rules as described below. Abstract classes cannot be instantiated but they can be subclassed. An abstract class is a class that is declared with abstract keyword.

When we write a program we dont want to think about the differences between all these platforms. An abstract class can have abstract and non abstract concrete methods and cant be instantiated with inheritance polymorphism abstraction encapsulation exception handling multithreading io streams networking string regex collection jdbc etc. An abstract machine has an instruction set a register set and a model of memory. Some of them can be concrete methods.

Abstract classes can include abstract and non abstract methods. An abstract class must be declared using the abstract keyword. Abstract machines are the core of what defines a programming language. Rules for using abstract classes in java.

They can include constructors and static methods. When java program runs into a computer it is executed in another virtual machine jvm for which the runtime environment is provided by jre java runtime environment it is installed automatically when you install jdk java development kit. An abstract method is a method that is declared without an implementation without braces and followed by a semicolon like this. Abstract class in java with abstract methods and examples.

It may provide instructions which are closer to the language being compiled than any physical computer or it may be used to make the language implementation easier to port to other platforms. Thus it must be possible to create a reference to an abstract class so that it can be used to point to a subclass object. A wide variety of operating systems and plethora of hardware ensures a bewildering number of things we call computers. Abstraction can be achieved with either abstract classes or interfaces which you will learn more about in the next chapter.

An abstract class cannot be instantiated. An abstract class may or may not have all abstract methods. What you describe is essentially what java and the jvm do currently. An abstract method is a method that is declared without an implementation.

Java is compiled to something called bytecode which is an intermediate language that happens to look an awful lot like assembly for a stack based machinethe jvm then interprets this code translating parts of it to machine code on the fly in a process called just in time jit compilation.