Java Requirements: Threes in Java

1. Expressions are made up of:	Variables Operators Literals Method calls
2. Three rules for overloaded methods:	They must have the same name They must be in the same class They must have different signatures (headers)
3. Three rules for overridden methods:	They must have the same name They must have the same signature (headers) They must be in different classes
4. Three rules for constructors:	The must have the name of the class in which they are contained The do not have a return type They are typically overloaded
5. Three uses of square brackets:	Used to declare an array Used to instantiate an array Used to reference an element of an array
6. Three uses of final:	Variables: create constants: public static final float PI = 3.14159f; Methods: prevents the method from being overridden in a subclass Classes: prevents the class from being extended.
7. Three uses of super:	Use to call a base class constructor Use to call a base class method that has been overridden. Use to reference a base class variable (shadow variables)
8. Three requirements for polymorphism:	There must be an inheritance hierarchy There must be overridden methods There must be a base class reference variable
9. Abstract classes may have:	Any number of fully implemented methods (zero or more) Any mixture of fully implemented and abstract methods Any number of constructors Any number of instance variables Any number of abstract methods (zero or more)
10. Interfaces may have:	Any number of method headers (public) Any number of constant definitions (public static final) Any mixture of methods headers and constants.