Java Terminology
Let us quickly go through some of the most important terms used in the Java programming language.
Java Virtual Machine (JVM)
The JVM stands for Java Virtual Machine. A program’s execution is divided into three stages. A Java program is written, compiled and then run.
As we can see in the above image, first the JVM language classes are processed by the class loader subsystem which is responsible for loading, linking and initialization of the java classes. After being processed by the class loader, the generated files are stored in the JVM Memory which consists of method area, heap, JVM language stacks, PC registers and native method stacks. The execution engine accesses the files from this JVM memory and makes use of the Native Method Interface and Native Method Libraries.
- A Java programmer creates a program.
- The JAVAC compiler, which is a primary Java compiler provided in the Java development kit (JDK), is used to compile the code. It accepts a Java application as input and outputs bytecode.
- JVM runs the bytecode generated by the compiler during the program’s Running phase.
The Java Virtual Machine’s job is to run the bytecode generated by the compiler. Although each operating system has its own JVM, the output they provide after bytecode execution is consistent across all of them. Java is known as a platform-independent language for this reason.
Bytecode
Bytecode is a type of intermediate code generated by the compiler after source code has been compiled (JAVA Program). Java is a platform-independent language thanks to this intermediate code.
Java Runtime Environment (JRE)
The Java Runtime Environment (JRE) is included with the JDK. The JRE installation on our computers allows us to run the Java program, but we cannot compile it. A browser, JVM, applet support, and plugins are all included in JRE. JRE is required for a computer to run a Java program.
In the above image, we can see that JVM together with the Java Class Libraries makes up the JRE.
Java Development Kit (JDK)
When we learn about bytecode and JVM, we use the name JDK. As the name implies, it is a complete Java development kit that includes everything from the compiler to the Java Runtime Environment (JRE), debuggers, and documentation. In order to design, compile, and run the java application, we must first install JDK on our computer.
In the above image, we can clearly see that JVM and the Library classes together make up the JRE. JRE when combined with Development Tools makes up JDK.
Garbage Collection
Garbage collection is the technique through which Java programs maintain their memory automatically. Java programs are compiled into bytecode that may be executed by a Java Virtual Machine, or JVM. Objects are produced on the heap, which is a part of memory devoted to the Java application, while it runs on the JVM. Some objects will become obsolete over time. To free up memory, the garbage collector detects these useless objects and deletes them.
Finalize method
It’s a method that the Garbage Collector calls shortly before deleting or destroying an object that’s suitable for Garbage Collection in order to do cleanup. Clean-up activity entails de-allocating or closing the resources associated with that object, such as Database Connections and Network Connections. It’s important to remember that it’s not a reserved keyword. Garbage Collector destroys the object as soon as the finalise method completes. The finalize method is found in the Object class and has the following syntax: protected void finalize throws Throwable{}
Since the finalize function is contained in the Object class and Object is the superclass of all Java classes, the finalize method is available to all Java classes. As a result, the garbage collector may invoke the finalize function on any java object. We must override the finalize method present in the Object class to specify our own clean-up activities since the finalize function in the Object class has an empty implementation.
