Файл JAVA

A .java file is a plain-text source code file written in the Java programming language. Java is an object-oriented programming language built around the concepts of classes and objects. .java source files are compiled by the javac compiler into .class bytecode files; to run the resulting program, a Java Virtual Machine (JVM) is required. Java is also the primary language used for developing Android applications.

Object-oriented programming

Java was heavily influenced by C++, though it was designed from the ground up as a platform-independent language. The original designers accepted some trade-offs in raw execution speed in order to achieve "write once, run anywhere" portability; modern JIT (just-in-time) compilation has since closed much of that gap. .java files are built almost entirely from class, interface, enum, and record declarations, with only a small set of primitive types (such as int, boolean, and double) falling outside the object model. By convention, each .java file contains exactly one public type, and the file name must match that type's name - for example, App.java must contain public class App.

For simplicity, a class is a generalization - a template - of an object:

• *Class:* human - *object:* Smith John
• *Class:* airplane - *object:* Boeing 737

Each class defines the properties an object can have (for example, a car may have properties such as color, number of seats, etc.) and the methods it can execute - that is, the operations or actions it can perform (for example, a car object can accelerate, brake, and sound a horn). Classes can inherit from other classes or compose other classes, enabling code reuse and modular design.

Compiling a .java file with javac produces a .class file; multiple .class files are commonly packaged into a JAR archive for distribution. Since Java 11, a single-file .java program can also be launched directly with the java command without an explicit compile step.