//Visitor //不是很理解这个有问题 import java.util.*; interface Visitor { public void visitString(StringElement stringE); public void visitFloat(FloatElement floatE); public void visitCollection(Collection collection); } //ConcreteVisitor class ConcreteVisitor implements Visitor { public void visitCollection(Collection collection) { // TODO Auto-generated method stub Iterator iterator = (Iterator)collection.iterator(); while (iterator.hasNext()) { Object o = iterator.next(); if (o instanceof Visitable) { ((Visitable)o).accept(this); } } } public void visitFloat(FloatElement floatE) { System.out.println(floatE.getFe()); } public void visitString(StringElement stringE) { System.out.println(stringE.getSe()); } } //Element interface Visitable { public void accept(Visitor visitor); } //ConcreteElement class FloatElement implements Visitable { private Float fe; public FloatElement(Float fe) { this.fe = fe; } public Float getFe() { return this.fe; } public void accept(Visitor visitor) { visitor.visitFloat(this); } } class StringElement implements Visitable { private String se; public StringElement(String se) { this.se = se; } public String getSe() { return this.se; } public void accept(Visitor visitor) { visitor.visitString(this); } } public class DS23_Visitor{ public static void main(String[] args) { Visitor visitor = new ConcreteVisitor(); StringElement se = new StringElement("abc"); se.accept(visitor); FloatElement fe = new FloatElement(new Float(1.5)); fe.accept(visitor); System.out.println("==========="); List result = new ArrayList(); result.add(new StringElement("abc")); result.add(new StringElement("abc")); result.add(new StringElement("abc")); //result.add(new FloatElement(new Float(1.5))); // result.add(new FloatElement(new Float(1.5))); //result.add(new FloatElement(new Float(1.5))); visitor.visitCollection(result); } }