Question

java抛出nulllpointerexception异常

代码如下import java.io.*;public class RandomAccessFileDemo { public static void RandomWriteFile(File file){  Employee[] employees=new Employee[4];  employees[0]=new Employee("张三",20);  employees[0]=new Employee("李四",21);  employees[0]=new Employee("王五",22);  employees[0]=new Employee("牛六",23);  RandomAccessFile randomaccessfile=null;  try{   randomaccessfile=new RandomAccessFile(file,"rw");  }catch(FileNotFoundException e){   e.printStackTrace();}  try{   for(Employee e1:employees){    randomaccessfile.writeChars(e1.getName());    randomaccessfile.writeInt(e1.getage());   }   randomaccessfile.close();  }catch(IOException e){e.printStackTrace();  } } private static String readName(RandomAccessFile randomaccessfile)throws IOException{  char[]name=new char[8];  for(int i=0;i<name.length;i++)   name[i]=randomaccessfile.readChar();   return new String(name).replace('\0',' ');    } public static Employee[]RandomReadFile(File file)throws Exception{  RandomAccessFile randomaccessfile=new RandomAccessFile(file,"r");  Employee[]employee=new Employee[4];  int num=(int)randomaccessfile.length()/Employee.size();  for(int i=0;i<num;i++){   randomaccessfile.seek((i)*Employee.size());   employee[i]=new Employee(readName(randomaccessfile),randomaccessfile.readInt());  }  randomaccessfile.close();  return employee;   } public static void main(String[] args)throws Exception {  String filename=args[0]==null?"E:\newfile.txt":args[0];  File file=new File(filename);  RandomWriteFile(file);  Employee[]employee=RandomReadFile(file);  for(Employee e:employee){   System.out.println("name="+e.getName()+"\t|\tage="+e.getage());  } }}class Employee{String name;int age;final static int Len=8;public Employee(String name,int age){ if(name.length()>Len){  name=name.substring(0,8);}  else{  while(name.length()<Len)   name=name+"\u0000";  } this.name=name; this.age=age;}public String getName(){ return name;}public int getage(){ return age;}public void setName(String name){ this.name=name;}public void setage(int age){ this.age=age;}public static int size(){ return 2*8+4;}}在DOS环境下运行提示nullpointerexception,行数分别书16和46

Answer 1

你好，有两处错误

1、
把employees[0]=new Employee("张三",20);
employees[0]=new Employee("李四",21);
employees[0]=new Employee("王五",22);
employees[0]=new Employee("牛六",23);
改为
employees[0] = new Employee("张三", 20);
employees[1] = new Employee("李四", 21);
employees[2] = new Employee("王五", 22);
employees[3] = new Employee("牛六", 23);

2、
把改为String filename=args[0]==null?"E:\newfile.txt":args[0];
改为String filename = !(args != null && args.length != 0 && args[0] != null) ? "e:\\newfile.txt" : args[0];

Answer 2

employees[0] = new Employee("张三", 20);
employees[0] = new Employee("李四", 21);
employees[0] = new Employee("王五", 22);
employees[0] = new Employee("牛六", 23);
给数组赋值的时候,你只给第0位赋了4个值,后面3个当然是空指针了

Answer 3

employees[0] = new Employee("张三", 20);
employees[1] = new Employee("李四", 21);
employees[2] = new Employee("王五", 22);
employees[3] = new Employee("牛六", 23);

Answer 4

从代码异常处的对象开始往前推啊, 自己找找看,你的格式这么烂,谁能知道你哪行是哪行,,,流汗!!!