java 创建自定义数组

1.java创建自定义类数组方法：

student []stu = new student[3];
for(int i = 0; i < 3; i ++)
{
stu[i] = new student();
｝

2.否则会提示空指针异常

package project;
 
import java.io.*;
import java.util.scanner;
class student
{
  private int id;
  private string name;
  private int score;
   
  public void setid(int id)
  {
    this.id = id;
  }
  public int getid()
  {
    return this.id;
  }
  public void setname(string name)
  {
    this.name = name;
  }
  public string getname()
  {
    return this.name;
  }
  public void setscore(int score)
  {
    this.score = score;
  }
  public int getscore()
  {
    return this.score;
  }
}
public class project2 {
  file file = new file("e:/data.txt");
  filewriter filewrite = null;
  bufferedwriter write = null;
  filereader fileread = null;
  bufferedreader read = null;
  student []stu = new student[3];
  public void put()
  {
    try {
      filewrite = new filewriter(file);
    } catch (ioexception e) {
      // todo 自动生成的 catch 块
      e.printstacktrace();
    }
    write = new bufferedwriter(filewrite);
    for(int i = 0; i < 3; i ++)
    {
      system.out.println("请输入第" + (i + 1) + "个学生的id,姓名,成绩:");
      scanner in = new scanner(system.in);
      try {
        string str = in.nextline();
        string data[] = str.split(" ");
        for(int j = 0; j < 3; j++)
        {
          write.write(data[j]);
          write.newline();
        }
         
      } catch (ioexception e) {
        // todo 自动生成的 catch 块
        e.printstacktrace();
      }
       
    }
    try {
      write.close();
      filewrite.close();
    } catch (ioexception e) {
      // todo 自动生成的 catch 块
      e.printstacktrace();
    }
  }
   
   
  public void get()
  {
    int sum = 0;
    double ave;
    try {
      fileread = new filereader(file);
    } catch (filenotfoundexception e) {
      // todo 自动生成的 catch 块
      e.printstacktrace();
    }
    read = new bufferedreader(fileread);
    for(int i = 0; i < 3; i ++)
    {
      stu[i] = new student();
      try {
        stu[i].setid(integer.parseint(read.readline()));
        stu[i].setname(read.readline());
        stu[i].setscore(integer.parseint(read.readline()));
      } catch (exception e) {
        // todo 自动生成的 catch 块
        e.printstacktrace();
      }
    }
     
    for(int i = 0; i < 3; i ++)
    {
      sum += stu[i].getscore();
    }
    ave = sum * 1.0/3;
    system.out.println("学生的平均成绩为：" + ave);
    try {
      read.close();
      fileread.close();
    } catch (ioexception e) {
      // todo 自动生成的 catch 块
      e.printstacktrace();
    }
  }
  public static void main (string []args)
  {
    project2 pro = new project2();
    pro.put();
    pro.get();
  }
}

    总结：

             这样我们就可以在项目当中,根据项目需求自己来定义想要的数组.