一个小小的java算法练习

最近项目中有一个页面运行非常慢，原来是数据从数据库取出简单封装成对象后直接以JSON的方式丢给 javascript 处理，对象个数比较多，甚至导致了浏览器报脚本运行太慢的警告。其中有一块代码写的不好懂，处理的逻辑大意是：从数据库返回3列比如A, B, C，其中A列有重复值，那么以A列的值进行group, 列B和C的值做成key-value的对象，整个数据处理完后，形成一个可以放进 HTML5 中的 <optgroup> 标签中的数据结构。下面是初始的 javascript 代码：

var technologyData = data.turbinesVO.technology;var technologyList = new Array();var stageCodeArray = new Array();var lastFrameType = technologyData[0].frameTypeGrp;for(var i=0;i<technologyData.length;i++){if(technologyData[i].frameTypeGrp == lastFrameType){var tempStageCode = {"optionId" : lastFrameType+"/"+technologyData[i].stageCode,"optionSn" : lastFrameType+" - "+technologyData[i].stageCode};stageCodeArray.push(tempStageCode);}else{var tempFrameType = {"groupName" : lastFrameType,"optionList" : stageCodeArray};technologyList.push(tempFrameType);stageCodeArray = new Array();var tempStageCode = {"optionId" : technologyData[i].frameTypeGrp+"/"+technologyData[i].stageCode,"optionSn" : technologyData[i].frameTypeGrp+" - "+technologyData[i].stageCode};stageCodeArray.push(tempStageCode);}lastFrameType = technologyData[i].frameTypeGrp;}var tempFrameType = {"groupName" : lastFrameType,"optionList" : stageCodeArray};technologyList.push(tempFrameType);

这个算法是基于数据对象 technologyData 已经根据 frameTypeGrp 进行排序（在数据库已经排好序了）。

理解了这个算法后，经考虑形成了下面的java算法：

Map<String, Technology> unikTechs = new HashMap<String, Technology>();Technology technology = null;// turbinesVO.getTechnology() returns target data which being handledfor (TechnologyDTO tech : turbinesVO.getTechnology()) {  // fameType is the column A, that becomes group key and will put into auxiliary collection unikTechs  String fameType = tech.getFrameTypeGrp();  // check whether there is already a Technology with this given group key - "fameType"  if (unikTechs.keySet().contains(fameType)){   technology = unikTechs.get(fameType);  } else {   // this means this group key is first time to come   technology = new Technology();   technology.setGroupName(fameType);   // associate to the final returned object "result" by result.getTechs()   result.getTechs().add(technology);      // update auxiliary collection for future examination   unikTechs.put(fameType, technology);  }      // construct column B&C as key-value to an option for <optgroup>  String stageCode = tech.getStageCode();    Pair pair = new Pair();  pair.setOptionId(fameType + "/" + stageCode);  pair.setOptionSn(fameType + " - " + stageCode);  // append this option to optionList under group key - "fameType"  technology.getOptionList().add(pair);}  

对应的辅助类：

public class Technology implements Comparable<Technology>{private String groupName;private List<Pair> optionList = new ArrayList<Pair>();@Overridepublic int compareTo(SiteTurbine o) {return this.groupName.compareTo(o.groupName);}public String getGroupName() {return groupName;}public void setGroupName(String groupName) {this.groupName = groupName;}public List<Pair> getOptionList() {return optionList;}public void setOptionList(List<Pair> optionList) {this.optionList = optionList;} }public class Pair{private String optionId;private String optionSn;public String getOptionId() {return optionId;}public void setOptionId(String optionId) {this.optionId = optionId;}public String getOptionSn() {return optionSn;}public void setOptionSn(String optionSn) {this.optionSn = optionSn;}}

经过修改后，算法更容易懂，而且数据对象可以是无序的（即没有按 fameType 进行字典排序），而且比较优雅。:)