Visitor Pattern(访问者模式）

 package visitor;import java.util.ArrayList;import java.util.List;abstract class carElement{public abstract void accept(carVisitor v);}interface carVisitor{void visit(carBody body);void visit(carWheel wheel);void visit(carEngine engine);void visit(car car);}class carBody extends carElement{public void accept(carVisitor v){v.visit(this);}}class carWheel extends carElement{public void accept(carVisitor v){v.visit(this);}}class carEngine extends carElement{public void accept(carVisitor v){v.visit(this);}}class car {private List<carElement> list=new ArrayList<carElement>();public void addElement(carElement element){list.add(element);}public void accpet(carVisitor v){for(carElement element:list){element.accept(v);}}}class carPrintVisitor implements carVisitor{public void visit(carBody body) {System.out.println("print : "+this.getClass().getName()+" visit "+body.getClass().getName());}public void visit(carWheel wheel) {System.out.println("print : "+this.getClass().getName()+" visit "+wheel.getClass().getName());}public void visit(carEngine engine) {System.out.println("print : "+this.getClass().getName()+" visit "+engine.getClass().getName());}public void visit(car car) {car.accpet(this);}}class carDoVisitor implements carVisitor{public void visit(carBody body) {System.out.println("Do : "+this.getClass().getName()+" visit "+body.getClass().getName());}public void visit(carWheel wheel) {System.out.println("Do : "+this.getClass().getName()+" visit "+wheel.getClass().getName());}public void visit(carEngine engine) {System.out.println("Do : "+this.getClass().getName()+" visit "+engine.getClass().getName());}public void visit(car car) {car.accpet(this);}}/** * @see visitor模式的两次分发形成了一个矩阵，每个单元都会被一项功能填充。 * @author http://en.wikipedia.org/wiki/Visitor_pattern * @author Owner * */public class VisitorApp {/** * @param args */public static void main(String[] args) {carWheel wheel=new carWheel();carBody body=new carBody();carEngine engine=new carEngine();car car=new car();car.addElement(wheel);car.addElement(body);car.addElement(engine);carVisitor visitor=new carPrintVisitor();visitor.visit(body);visitor.visit(engine);visitor.visit(wheel);visitor.visit(car);visitor=new carDoVisitor();visitor.visit(body);visitor.visit(engine);visitor.visit(wheel);visitor.visit(car);}} 

 

参考：http://en.wikipedia.org/wiki/Visitor_pattern