Visitor模式
import java.util.ArrayList;import java.util.Collection;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}interface Element{ public void accept(Visitor visitor);}class ConcreteVisitor implements Visitor{//具体的访问者 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 "); }}class ConcreteElementA implements Element{//具体元素A 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; }}class ConcreteElementB implements Element{//具体元素B 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); } }class ObjectStructure{//对象结构即元素的集合 private Collection<Element> collection=new ArrayList<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); } }
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