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.