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What is a NullPointerException, and how do I fix it?

(12个答案)


4年前关闭。




谁能告诉我下面的代码为什么会有NullPointerException?我试图弄清楚,但不能!

以下行是例外:

companies[x].compName=temp1[0];


companies数组类型为Company,其中包含字符串和数组列表。

JFileChooser  fileChooser = new JFileChooser();                             // create instence from file chooser
fileChooser.setCurrentDirectory(new File(System.getProperty("user.home"))); //assign directory

if(fileChooser.showOpenDialog(null)==JFileChooser.APPROVE_OPTION){
    File f = fileChooser.getSelectedFile();
    try{

        LineNumberReader  lnr = new LineNumberReader(new FileReader(f));
        lnr.skip(Long.MAX_VALUE);
        int n = lnr.getLineNumber() +1;

        lnr.close();
        companies = new Company[n];
        int i=0 , x=0;
        String s ="";
        Scanner input = new Scanner(f);
        String  [] temp1,temp2;
        while(input.hasNext()){     // read line by line

            s = input.nextLine();
            s=s.replaceAll(" ", "");
            if(s == null)
            continue;
            else{

                temp1 =s.split(",");
                companies[x].compName=temp1[0];           //store compName in the companies
                for( i=1;i<temp1.length;i++){


                    temp2=temp1[i].split("/");
                    companies[n].compItems.addLast(temp2[0], Integer.parseInt(temp2[1]));

                }  //end for
            }   //end else
            x++;
        }  //end while

最佳答案

请参阅我的评论-company [x]从未被初始化为Company()。初始化数组是不够的-数组中的每个项目也都需要分配。

您最好使用List,因为用于初始化数组的行数可能根本不是公司数(跳过了一些行)

while(input.hasNext()){     // read line by line

        s = input.nextLine();
        s=s.replaceAll(" ", "");
        if(s == null)
        continue;
        else{

            temp1 =s.split(",");
            //companies[x] is still null - initialize this!
            companies[x] = new Company();
            //Now this should be fine
            companies[x].compName=temp1[0];           //store compName in the companies
            for( i=1;i<temp1.length;i++){

08-05 04:17
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