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.

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