Design mode-Simple Factory mode

A simple factory model is a factory object (Factory) that determines which product class instances are created.

Requirements: Simulate a calculator class

First, define an abstract operator class

1  PackageCom.sun.FactoryMethod;2 3  Public Abstract classabsoperation {4     protectedDouble _numbera =0d;5     protectedDouble _numberb =0d;6 7      PublicDouble Get_numbera () {8         return_numbera;9     }Ten  One      Public voidSet_numbera (Double _numbera) { A          This. _numbera =_numbera; -     } -  the      PublicDouble Get_numberb () { -         return_numberb; -     } -  +      Public voidSet_numberb (Double _numberb) { -          This. _numberb =_numberb; +     } A  at     protected AbstractDouble GetResult (); -}

An abstract method that inherits an abstract class that implements a number addition:

1  PackageCom.sun.FactoryMethod;2 3  Public classOperationaddextendsabsoperation {4 5 @Override6     protectedDouble GetResult () {7Double result =0d;8result = _numbera +_numberb;9         returnresult;Ten     } One}

An abstract method that inherits an abstract class that implements a number subtraction:

1  PackageCom.sun.FactoryMethod;2 3  Public classOperationsubextendsabsoperation {4 5 @Override6     protectedDouble GetResult () {7Double result =0d;8result = _numbera-_numberb;9         returnresult;Ten     } One}

Provide a factory class, according to the operator to instantiate a calculation instance, the resulting absoperation is actually a reference to his child (Java sub-class can be cast to the parent class, the parent class cannot be cast to subclass, unless

A reference to a parent class is a pointer to a subclass):

1  PackageCom.sun.FactoryMethod;2 3  Public classOperationfactory {4      Public StaticAbsoperation Createoperate (Charoperate) {5Absoperation operation =NULL;6         Switch(operate) {7          Case+:8Operation =NewOperationadd ();9              Break;Ten          Case‘-‘: OneOperation =Newoperationsub (); A              Break; -         default: -Operation =NewOperationadd (); the              Break; -         } -  -         returnoperation; +     } -}

Here is the test class

1  PackageCom.sun.FactoryMethod;2 3  Public classtestoperation {4 5      Public Static voidMain (string[] args) {6 absoperation Operadd;7Operadd = operationfactory.createoperate (' + '));8Operadd._numbera =1d;9Operadd._numberb =2d;Ten System.out.println (Operadd.getresult ());//3.0 One          A absoperation opersub; -Opersub = Operationfactory.createoperate ('-')); -Opersub._numbera =2d; theOpersub._numberb =4d; - System.out.println (Opersub.getresult ());//-2.0 -     } -  +}

Here, by the way, a switch case statement is noted here that the parameters of switch () are not supported by strings (string) before jdk1.7, and are now supported;

So what happens if I don't write a break when I'm in the switch case?

If our case ' + ' does not write a break, then he will always find the next method of break to return; the result of Test return is -1,-2;

If it is our case '-' without a break, then he will always find the next method of break to return; then he will go to default: if there is another ' * ' behind case '-', then he will instantiate ' * '

The result, of course, we have to ensure that ' * ' has a break;

The default, he does not need to break;

Design mode-Simple Factory mode