Favor static member classes over nonstatic

Here are 4 types of nested class.

• static member class
• none-static member class
• anonymous class
• local class

 

• Anonymous Class & Local Class: Both are defined inside method or constructor of enclosing class.

If the class belongs inside a method/constructor, if you need to create instances from only one location and there is a preexisting type that characterizes the class, make it an anonymous class; else make it a local class.

• Static member class & none-static: these classes defined in enclosing class.

If each instance of the member class needs a reference to its enclosing instance, make it nonstatic;

 

• Static member class:

Can be instanced directlly, no need to instance the outer class first.

Eg. MyTest.StaticInnerClass sic = new MyTest.StaticInnerClass();

• None-static member class:

Instance a none-static member class should create outer class first:
MyTest.InnerClass mi = new MyTest().new InnerClass();

• Conclusion:

The static member class needn't instance the outer class, so it construct more efficient and less memory than none-static.