Java设计模式-----Visitor访问者模式

public interface Visitor {
public void visitElementA(ConcreteElementA elementA);//针对具体元素A的新方法
public void visitElementB(ConcreteElementB elementB);//针对具体元素B的新方法
}

public interface Element {
public void accept(Visitor visitor);
}

public class ConcreteVisitor implements Visitor {

public void visitElementA(ConcreteElementA elementA) {
System.out.println(elementA.getName() + " visited by ConcreteVisitor ");
}

public void visitElementB(ConcreteElementB elementB) {
System.out.println(elementB.getName() + " visited by ConcreteVisitor ");
}
}

public class ConcreteElementA implements Element {

private String name;

public ConcreteElementA(String name) {
this.name = name;
}

public void accept(Visitor visitor) {// 接受访问者调用它针对该元素的新方法
visitor.visitElementA(this);

}

public String getName() {
return name;
}
}

public class ConcreteElementB implements Element {

private String name;

public ConcreteElementB(String name) {
this.name = name;
}

public String getName() {
return name;
}

public void accept(Visitor visitor) {// 接受访问者调用它针对该元素的新方法
visitor.visitElementB(this);
}
}

public class ObjectStructure {

private Collection<element></element> collection = new ArrayList<element></element>();

public void attach(Element element) {
collection.add(element);
}

public void detach(Element element) {
collection.remove(element);
}

public void accept(Visitor visitor) {
for (Element element : collection) {
element.accept(visitor);
}
}
}

public class Client {

public static void main(String args[]) {

Element elementA = new ConcreteElementA("ElementA");
Element elementB = new ConcreteElementB("ElementB");
Visitor visitor = new ConcreteVisitor();

ObjectStructure os = new ObjectStructure();
os.attach(elementA);
os.attach(elementB);
os.accept(visitor);
}
}