软件设计模式

一、访问者模式（Visitor）

abstract class Element {
public abstract void accept(IVisitor visitor);
public abstract void doSomething();
}

interface IVisitor {
public void visit(ConcreteElement1 el1);
public void visit(ConcreteElement2 el2);
}

class ConcreteElement1 extends Element {
public void doSomething(){
System.out.println("这是元素1");
}

public void accept(IVisitor visitor) {
visitor.visit(this);
}
}

class ConcreteElement2 extends Element {
public void doSomething(){
System.out.println("这是元素2");
}

public void accept(IVisitor visitor) {
visitor.visit(this);
}
}
class Visitor implements IVisitor {

public void visit(ConcreteElement1 el1) {
el1.doSomething();
}

public void visit(ConcreteElement2 el2) {
el2.doSomething();
}
}

class ObjectStruture {
public static List<Element> getList(){
List<Element> list = new ArrayList<Element>();
Random ran = new Random();
for(int i=0; i<10; i++){
int a = ran.nextInt(100);
if(a>50){
list.add(new ConcreteElement1());
}else{
list.add(new ConcreteElement2());
}
}
return list;
}
}

public class Client {
public static void main(String[] args){
List<Element> list = ObjectStruture.getList();
for(Element e: list){
e.accept(new Visitor());
}
}
}