61B-1: Intro, Hello World Java

java oop

Java is an object oriented language with strict requirements:

• Every Java file must contain a class declaration*.
• All code lives inside a class*, even helper functions, global constants, etc.
• To run a Java program, you typically define a main method using

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public static void main(String[] args)

*: This is not completely true, e.g. we can also declare “interfaces” in .Java files that may contain code. We’ll cover these later.

Java and Static Typing

The compiler checks that all the types in your program are compatible before the program ever runs! This is unlike a language like Python, where type checks are performed DURING execution.