java问题日常积累

阳光穿透心脏的1/2处 2022-07-15 07:58 143阅读 0赞

写Android时总是遇到空指针问题，主要的原因是因为好多时候类没有初始化的缘故。

public class XMLParserHandler extends DefaultHandler \{  
private Book book=new Book();  
private ArrayList<Book> booklist=new ArrayList<Book>();  
private String nodeName;  
private StringBuilder value;  
@Override  
public void startDocument() throws SAXException \{  
// TODO Auto-generated method stub  
super.startDocument();  
value=new StringBuilder();  
\}  
  
  
@Override  
public void endDocument() throws SAXException \{  
// TODO Auto-generated method stub  
super.endDocument();  
\}  
  
  
@Override  
public void startElement(String uri, String localName, String qName,  
Attributes attributes) throws SAXException \{  
// TODO Auto-generated method stub  
super.startElement(uri, localName, qName, attributes);  
nodeName=localName;  
value.setLength(0);  
\}  
  
  
@Override  
public void endElement(String uri, String localName, String qName)  
throws SAXException \{  
// TODO Auto-generated method stub  
super.endElement(uri, localName, qName);  
if(qName.equals("data"))\{  
booklist.add(book);  
\}  
\}  
@Override  
public void characters(char\[\] ch, int start, int length)  
throws SAXException \{  
// TODO Auto-generated method stub  
super.characters(ch, start, length);  
value.append(ch,start,length);  
Log.d("mainactivity",value.toString().trim());  
  
if(nodeName.equals("id"))\{  
book.setId(Integer.parseInt(value.toString().trim()));  
\}else if(nodeName.equals("study\_number"))\{  
book.setStudy\_number(Integer.parseInt(value.toString().trim()));  
\}else if(nodeName.equals("name"))\{  
book.setName(value.toString().trim());  
\}else if(nodeName.equals("sex"))\{  
book.setSex(value.toString().trim());  
\}else if(nodeName.equals("major"))\{  
book.setMajor(value.toString().trim());  
\}else if(nodeName.equals("enroll\_year"))\{  
   book.setEnroll\_year(Integer.parseInt(value.toString().trim()));  
\}else if(nodeName.equals("class"))\{  
book.setClassw(value.toString().trim());  
\}else if(nodeName.equals("telephone"))\{  
book.setTelephone(value.toString().trim());  
\}else if(nodeName.equals("qq"))\{  
book.setQq(value.toString().trim());  
\}else if(nodeName.equals("email"))\{  
book.setEmail(value.toString().trim());  
\}else if(nodeName.equals("remark"))\{  
book.setRemark(value.toString().trim());  
\}  
\}  
  
  
public ArrayList<Book> getBooklist() \{  
return booklist;  
\}  
  
  
public void setBooklist(ArrayList<Book> booklist) \{  
this.booklist = booklist;  
\}