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java之创建自定义类数组

2013-12-06           来源：每天进步一点点 时间会让你成为巨人   

    

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();

｝

否则会提示空指针异常

eg：

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();	}}

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