Please is there any structure to follow in java programming, so my code can be easier to understand and low consumption of space

Answer 1

http://google.github.io/styleguide/javaguide.html

Answer 2

check out java documentation, using it for your program will help yourself and others better understand what your code is doing, also space wise i looked up one class in the java library and it had almost 2000 lines of code, which is awesome, but using nested classes and anonymous classes can help on space as well as functional interfaces with lambda expressions, but if you are new to java you should give these concepts a while before you look into them. also use variable and class names that can easily identify what is being done and used and your program almost documents itself