是(int)(Math.random()*1000000);不是((int)Math.random()*1000000);

本文链接：https://blog.youkuaiyun.com/robert_lizhiqiang/article/details/39855781

本文详细阐述了在使用Java IO库进行文件写入时遇到的常见问题，通过实例演示了错误原因及正确解决方案。重点讨论了在处理随机数生成与文件写入之间的同步问题，以及避免在读取前关闭文件流的重要性。

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今天在写一个IO程序的时候，出现了以下问题：

package io;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;

public class Buffer {
	public static void main(String[] args) {
		
		try {
			//FileReader one = new FileReader("D:" + File.separator + "one.txt");
			FileWriter owe = new FileWriter("D:" + File.separator + "one.txt");
			//BufferedReader br = new BufferedReader(one);
			BufferedWriter bw = new BufferedWriter(owe);
			for (int i = 0; i < 100; i++) {
				int j = ((int)Math.random()*1000000);
				bw.write(j);
				System.out.println(j);
				bw.newLine();
			}
			bw.flush();
			bw.close();
			System.out.println("done!");
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

总是写不到文件里面，我还以为怎么回事，打印出来一看，全都是0！

后来改掉，问题才得以解决！

我们知道，如果程序如下，k肯定等于100：

package io;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class Buffer {
	public static void main(String[] args) {
		int k = 0;
		try {
			String s = null;
			FileReader one = new FileReader("D:" + File.separator + "one.txt");
			FileWriter owe = new FileWriter("D:" + File.separator + "one.txt");
			BufferedWriter bw = new BufferedWriter(owe);
			BufferedReader br = new BufferedReader(one);
			for (int i = 0; i < 100; i++) {
				int j = (int)(Math.random()*1000000);
				bw.write(j);
				//System.out.println(j);
				bw.newLine();
			}
			bw.flush();
			while ((s = br.readLine()) != null) {
				System.out.println(s);
				k++;
			}
			System.out.println(k + "   KKKKKKKKKKKKKK      ");
			
			bw.close();
			br.close();
			System.out.println("done!");
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

程序如果如此，你猜K打印出来是多少行呢？（k = 50）为什么呢？

package io;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class Buffer {
	public static void main(String[] args) {
		int k = 0;
		try {
			String s = null;
			FileReader one = new FileReader("D:" + File.separator + "one.txt");
			FileWriter owe = new FileWriter("D:" + File.separator + "one.txt");
			BufferedWriter bw = new BufferedWriter(owe);
			BufferedReader br = new BufferedReader(one);
			for (int i = 0; i < 100; i++) {
				int j = (int)(Math.random()*1000000);
				bw.write(j);
				//System.out.println(j);
				bw.newLine();
			}
			bw.flush();
			while ((br.readLine()) != null) {
				System.out.println(br.readLine());
				k++;
			}
			System.out.println(k + "   KKKKKKKKKKKKKK      ");
			
			bw.close();
			br.close();
			System.out.println("done!");
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

也行，你觉得应该是99，因为在while的时候，少了一行嘛

但是结果是（k = 50）为什么呢？

因为，每次都会在while里面判断，所以每次都会少一行！