Notes for Java programmers: The Wolfram Language is interpreted, meaning any piece of code can be run immediately. Java code must be compiled before execution, making truly interactive programming impossible.

Notes for Python programmers: You can use the Wolfram Language interactively, like a much-enhanced version of the Python interactive shell, that supports immediate code assistance, graphics, inline interfaces, etc.

In a Wolfram Notebook on the desktop or web, just type an input, then press SHIFT+ENTER to compute:

In[1]:= 1 2 + 2

Out[1]= 1

In[2]:= 2 Range[10]