Question

我已将值分配给Report Info类的成员，并尝试添加到Report Group类。获取java null指针异常。即使我已经在一开始就初始化了报告Info。

执行此操作时出错 - reportGroup.getReportList（）。add（reportInfo）;

我有两个java类。

 ReportGroup.java
    String GroupName;
    List<ReportInfo>reportList; 

    public String getReportGroupName() {
    return ReportGroupName;
}
public void setReportGroupName(String reportGroupName) {
    ReportGroupName = reportGroupName;
}
public List<ReportInfo> getReportList() {
    return reportList;
}
public void setReportList(List<ReportInfo> reportList) {
    this.reportList = reportList;
}

}

ReportInfo.java
    String ReportName;
    String ReportId;
    String ReportPath;
    //Getter and Setter

主要课程：

public class test {
 List<ReportInfo> reportInfo = new ArrayList<ReportInfo>();

public static void main(String[] args) throws IOException {
    String orgId="346";
    String orgName="Ralph Lauren Corporation";

    String reportPath= "/"+orgId +"_"+orgName.replaceAll(" ","_");
    String reportFolderPath = "C:/Lokesh/Dev Tools/apache-tomcat-6.0.37/webapps/ROOT/Reports";
    List<String> filesArray = null;
    filesArray = new ArrayList<String>();

    String filetowrite="C:/Users/lbandhu/Desktop/test.html";
    FileWriter fw=new FileWriter(filetowrite);

    ReportGroup reportGroup=new ReportGroup();
    reportGroup.setReportGroupName(orgName); //Organization Name such as Ralph Lauren Corporation

    fw.write("<html><head><title>"+ reportGroup.ReportGroupName+"</title><h1>Utilization Report</h1><span>Please contact your account manager for a listing of utilization report definitions or with any questions on your organization’s reports. </span><br></head><body><table>");
    //fw.write("<br><h>"+orgName+"</h><br>");


    File folder = new File(reportFolderPath+reportPath);

    List<String> reportNames =  listFolder(folder);


    for (String rname : reportNames) {
        ReportInfo reportInfo=new ReportInfo();
        reportInfo.setReportName(rname);

        folder = new File(reportFolderPath+reportPath+"/"+reportInfo.ReportName);
        System.out.println(folder);
        fw.write("<br><tr> "+reportInfo.ReportName +" Utilization Reports</tr><br>"); //Report Name such as Monthly,Quarterly and Yearly
        Iterator<String> iterator=listFilesForFolder(folder, filesArray).iterator();
        writeReportPath( fw,iterator, reportFolderPath,reportInfo);
        fw.write("<br>");
        reportGroup.getReportList().add(reportInfo); 
    }
    filesArray.clear();
    fw.close();

}

Answer 1

您需要在构造函数中初始化列表：

 public ReportGroup(){
     reportList  = new ArrayList<ReportInfo>();
 }

或

 public ReportGroup(String GroupName){
     this.GroupName = GroupName;
     reportList  = new ArrayList<ReportInfo>();
 }

Answer 2

您正在初始化reportInfo课程的test个字段，而不是reportInfo的字段ReportGroup。看起来你实际上并不是你的test类，并且这个字段对于静态（即类）方法是不可见的。即使它是可见的（例如，如果它本身是静态的），你也会用局部变量reportInfo来遮蔽它。

当您在ReportInfo reportInfo = new ReportInfo()循环的第一行中for时，您正在创建一个新的ReportGroup，其中包含一个未初始化的新reportInfo成员。

您的ReportGroup应该是这样的：

class ReportGroup {
    final List<ReportInfo> reportInfo = new ArrayList<>();
}

或者，您可以在构造函数中进行初始化：

class ReportGroup {
    final List<ReportInfo> reportInfo;

    ReportGroup () {
        reportInfo = new ArrayList<ReportInfo>;
    }
}

将对象类添加到reportGroup.getReportList（）时获取java空指针异常

2 个答案: