Java Language

Strict object-oriented programming language.

• Forces an object-oriented model where the main method is in a class.

• Forces a one-class-per-file approach.

  • The name of the file must match the public class in the source code.

Can be used in a wide range of scenarios.

• Mobile: Android applications <- focus of this class.

• Desktop: CLI or Desktop applications.

• Server: Web apps using application servers.

• Web: Java Applets, and Java Web Start, sometimes via Java Network Launch Protocol.

  • Mostly dead as browsers dropped support due to security concerns.

Promotes the motto: Write once, run anywhere.

• Enabled by using bytecode instead of machine code.

Bytecode runs on a Java Virtual Machine.

• JVM implementation interprets bytecode in a pseudo-CPU.

• JVM is implemented natively for each supported architecture.

• Host architectural aspects are not directly exposed to applications.

  • Access is mediated (and limited) by the interfaces exposed by the JVM.

Source files must have .java extension.

• import statement can be used to get features from other classes.

Compiled bytecode is in .class files.

• The class filename matches the class inside, which enables dynamic, on-demand loading.

• For nested classes, the name of the .class file also reflects this structure.