Java Fundamentals: why Java succeeded

Java gained momentum because its portability proposition solved an important problem: running software in different environments with less platform dependence.

The Java context

Java was publicly introduced in 1995, during a period of strong internet growth.

The language’s proposition was closely tied to portability.

In other words, the idea was to allow Java programs to run on different operating systems and architectures, as long as a compatible JVM existed in that environment.

This point matters: Java does not run automatically on any machine without preparation.

It depends on a suitable Java Virtual Machine to execute the bytecode.

Java portability

Java’s portability is directly linked to the JVM, short for Java Virtual Machine.

The JVM can exist on different operating systems and servers.

With that, the same Java program can run in different environments without the programmer needing to rewrite all the code for each system.

This separation was one of the language’s great advantages.

How Java code works

The programmer writes a file with Java code.

That code has commands, syntax rules, and meaning defined by the language.

This is the code we can read and write as developers.

Then, that code goes through compilation.

Compilation checks language rules and transforms the source code into an intermediate format that the JVM can execute.

The .class file

After compilation, Java generates .class files.

A .class file follows a specific format and contains class information, plus instructions called bytecodes.

These bytecodes were not made to be read directly by humans in day-to-day work.

They are instructions understood by the JVM.

Simply put:

.java  -> código-fonte Java
.class -> arquivo gerado pela compilação, com bytecodes

The role of bytecodes

Bytecodes are intermediate instructions.

They don’t depend directly on a single operating system, as would happen with a platform-specific native executable.

The JVM understands these bytecodes and runs the program in the environment where it is installed.

In an introductory explanation, we can say the JVM interprets bytecodes.

But in modern JVMs, parts of the program can also be optimized and compiled during execution.

Why this helped Java grow

This architecture helped Java become a relevant language because it reduced the direct coupling between the program and the operating system.

The developer writes the Java code and compiles it to bytecode.

Then, a compatible JVM runs that bytecode in different environments.

This made Java easier to use in varied scenarios, such as enterprise applications, servers, web systems, and large-scale software.

Recap

Java succeeded for several reasons, but portability was one of the most important.

The central idea is:

1. the developer writes Java code;
2. the code is compiled;
3. compilation generates .class files;
4. the .class files contain bytecodes;
5. the JVM executes those bytecodes;
6. the program can run in different environments with a compatible JVM.

This combination made Java a strong language for systems that need to work on different platforms.