What you are asking is a pretty tough question. While you may think it is just one question, you are actually asking several questions at once. I’ll do my best with the knowledge that I have to cover it and, hopefully, some others will join in to cover what I may miss. Nested Classes: Introduction … Read more
static class Thing will make your program work. As it is, you’ve got Thing as an inner class, which (by definition) is associated with a particular instance of Hello (even if it never uses or refers to it), which means it’s an error to say new Thing(); without having a particular Hello instance in scope. … Read more
An inner class, by definition, cannot be static, so I am going to recast your question as “What is the difference between static and non-static nested classes?” A non-static nested class has full access to the members of the class within which it is nested. A static nested class does not have a reference to … Read more
… starting in Java SE 8, a local class can access local variables and parameters of the enclosing block that are final or effectively final. A variable or parameter whose value is never changed after it is initialized is effectively final. For example, suppose that the variable numberLength is not declared final, and you add … Read more
ZShape is not static so it requires an instance of the outer class. The simplest solution is to make ZShape and any nested class static if you can. I would also make any fields final or static final that you can as well.
From the Java Tutorial: Nested classes are divided into two categories: static and non-static. Nested classes that are declared static are simply called static nested classes. Non-static nested classes are called inner classes. Static nested classes are accessed using the enclosing class name: OuterClass.StaticNestedClass For example, to create an object for the static nested class, … Read more