Design pattern Start-visitor mode

Visitor mode

First, the role

(1) The visitor pattern is suitable for the system with relatively stable data structure, separating the processing from the information structures, when the system has a relatively stable data structure and easy to change algorithm, the visitor pattern is more applicable.

(2) The purpose is to encapsulate an operation applied to a data structure element, and to add a new mode of operation without modifying the original system.

Second, class diagram

Third, the realization

(1) IShape defines the current operational requirements and the visitor to be accepted

 Public InterfaceIShape { Public floatGetarea ();  PublicObject Accept (Ivisitor visitor);} Public classTriangleImplementsIShape {floatX1,y1,x2,y2,x3,y3;  PublicTriangle (floatX1,floatY1,floatX2,floatY2,floatX3,floaty3) {         This. X1 =X1;  This. Y1 =Y1;  This. x2 =x2;  This. y2 =Y2;  This. x3 =X3;  This. Y3 =Y3; }     Public floatGetdist (floatU1,floatV1,floatU2,floatv2) {        return(float) math.sqrt ((U1-U2) * (U1-U2) + (V1-V2) * (v1-v2)); } @Override Public floatGetarea () {floatA =getdist (X1,Y1,X2,Y2); floatb =getdist (X1,Y1,X3,Y3); floatc =getdist (X3,Y3,X2,Y2); floats = (a+b+c)/2; return(float) math.sqrt (s* (s-a) * (s-b) * (S-c)); } @Override PublicObject Accept (Ivisitor visitor) {returnVisitor.visitor ( This); }}

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(2) Ivisitor defining the objects to be accepted and the new functions implemented after accepting objects

 public  interface   Ivisitor {Object visitor (Triangle t);}  public  class  Lengthvisitor implements   Ivisitor {@Override 
    public   Object Visitor (Triangle t) {        float  a = T.getdist (t.x1,t.y1,t.x2,t.y2);  float  b = T.getdist (t.x1,t.y1,t.x3,t.y3        );  float  C = T.getdist (t.x3,t.y3,t.x2,t.y2        );     return  a+b+C; }}

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(3) client Customer test class

 Public class Client {    publicstaticvoid  main (string[] args) {        new  lengthvisitor ();         New Triangle (0,0,2,0,0,2);        Shape.accept (visitor);        System.out.println (Shape.getarea ());        System.out.println (Visitor.visitor (Shape));}    }

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Design pattern Start-visitor mode