Composition of classes
1 . Attributes
(1) Attributes are also called member variables.
(2) Syntax: data type variable names;
(3) Definition location: within the class, but outside the method.
2 . Method
(1) Method is also called member method.
(2) Define the method name of public return value type(parameter list){//Method implementation}
(3) Note that static is not added when defining the method here.