This cheat sheet, from Princeton University's Introduction to Programming in Java course, makes a great reference for the basics you need to know, like structure, input/output, data types ...

How to recognize and use array and list data structures in your Java programs. Which algorithms work best with different types of array and list data structures. Why some algorithms will work ...

Java programmers use data structures to store and organize data, and we use algorithms to manipulate the data in those structures. The more you understand about data structures and algorithms ...