java筆記八：IO流之字符流與字符緩沖流

　　java中字符流主要都是繼承於Reader和Writer兩個抽象類。用於對字符文本的讀寫操作。

 

一、轉換類流

package com.iotest;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class ConverseStreamDemo {

    public static void main(String[] args) {
        String s = "F:\\shar\\test\\test3.txt";
        try {
            //將字節流轉為字符流
            OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream(s));
            osw.write("中國北京");
            System.out.println(osw.getEncoding());
            osw.close();
            osw = new OutputStreamWriter(new FileOutputStream(s,true),"GB2312");
            osw.write("中國北京");
            System.out.println(osw.getEncoding());
            osw.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {
            //將字節流轉為字符流
            InputStreamReader isr = new InputStreamReader(new FileInputStream(s),"GB2312");
            int c;
            while((c=isr.read()) != -1){
                System.out.print((char)c);
            }
            System.out.println();
            isr.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        }
    }

}

 

二、FileReader和FileWriter

package com.iotest;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
/*
 * 使用flush（）將流數據刷到目標里，這時流還存活着，還可以繼續使用該流進行別的操作。
 * close（）雖然也有flush（）的效果但是這時流已經死了，你如果想繼續使用流的話就必須在此建立流
 */
public class MutiplicationTable {
    
    public static void main(String[] args) throws IOException {
        String s = "F:\\shar\\test\\test5.txt";
        FileWriter fw = new FileWriter(s);
        FileReader fr = new FileReader(s);
        for (int i = 1; i <= 9; i++) {
            for (int j = 1; j <= i; j++) {
                String str = i + "*" + j + "=" + i*j + " ";
                fw.write(str);
            }
            fw.write("\r\n");
            /*flush是指強行將輸出流中的數據寫到文件里面去。如果寫到這里的話就是一行一行的寫入文件
             *最好每寫完一部分就刷新一次，如果最后刷新的話可能會造成數據的丟失
             */
            fw.flush(); 
        }
        //如果又不寫flush()又不寫close()，則不會寫入任何內容到文本里。只是寫到了緩沖區
        //fw.flush(); 寫到這里的話就是所有的內容一起寫進文件
        //fw.close(); close之前會調用flush()
        //讀字符輸入流的數據
        int c;
        while ((c=fr.read())!=-1) {
            System.out.print((char)c);
        }
    }

}

 

三、BufferedReader和BufferedWriter

package com.iotest;

import java.io.BufferedOutputStream;
import java.io.BufferedWriter;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;

public class PrimeNumber {
    BufferedWriter bw = null;
    String fileName = "F:\\shar\\test\\test7.txt";
    //判斷是否是質數
    public boolean isPrime(int n){
        for(int i=2;i<=n/2;i++){
            if(n%i == 0){
                return false;
            }
        }
        return true;
    }
    void printPrime(int m) throws IOException{
        //將字節流轉緩沖流
        bw = new BufferedWriter(new FileWriter(fileName));
        int j = 0;
        for (int i = 2; i < m; i++) {
            if(isPrime(i)){
                j++;
                String s = String.valueOf(i);
                String s1 = s + " ";
                bw.write(s1);  //寫入文本文件
                if(j==10){
                    j = 0;
                    bw.newLine();  //寫入一個行分隔符
                    bw.flush();  //強制刷新
                }
            }
        }
        
        bw.close();
    }
    public static void main(String[] args) throws IOException {
        PrimeNumber pn = new PrimeNumber();
        pn.printPrime(100);
    }

}

四、PrintWriter

package com.iotest;

import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

public class PrintWriterDemo {

    public static void main(String[] args) throws IOException {
        int A = 0;  //千位
        int B = 0;  //百位
        int C = 0;  //十位
        int num = 0;
        String fileName = "F:\\shar\\test\\test8.txt";
        FileWriter fw = new FileWriter(fileName); //字符輸出流
        PrintWriter pw = new PrintWriter(fw);     //將字節輸出流轉為PrintWriter
        for (int i = 1000; i < 10000; i++) {
            A = i/1000;
            B = i/100 % 10;
            C = i/10 % 10;            
            if(i%11==0 && A == B+C){
                pw.print(i+" ");
                if(++num % 7 == 0){
                    pw.println();  //寫入回車換行
                    pw.flush();    //強制刷新流
                }
            }
        }
        fw.close();
        
    }

}

五、標准IO

package com.iotest;

import java.io.BufferedReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Scanner;

public class PackStardIO {

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter o = new PrintWriter(System.out);  //包裝標准輸出
        String s;
        while((s=br.readLine())!=null && s.length()!=0){
            o.println(s.toUpperCase());
            //o.flush();   //一定要強制刷新讓其輸出來，否則不會輸出
        }
    }

}

 

package com.iotest;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;

public class StandardIORedirect {

    public static void main(String[] args) throws IOException {
        PrintStream console = System.out;
        BufferedInputStream in = new BufferedInputStream(new FileInputStream("C:\\Documents and Settings\\01\\桌面\\Test\\src\\com\\iotest\\StandardIORedirect.java"));
        PrintStream out = new PrintStream(new BufferedOutputStream(new FileOutputStream("F:\\shar\\test\\test9.txt")));
        System.setIn(in);     //對標准輸入流重定向
        System.setOut(out);
        System.setErr(out);
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String s;
        while((s=br.readLine())!=null){   //從BufferedReader中讀取一行數據
            System.out.println(s);
        }
        out.close();
        System.setOut(console);
    }

}

六、隨即訪問文件類

package com.iotest;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;

public class RandomRW {
    public static void main(String[] args) throws IOException {
        RandomAccessFile raf = new RandomAccessFile("F:\\shar\\test\\test10.dat","rw");
        final int DOUBLE_SIZE = 8;
        for (int i = 0; i < 10; i++) {
            raf.writeDouble(i);
            System.out.print(" " + (double)i);
        }
        System.out.println();
        raf.close();
        RandomAccessFile raf1 = new RandomAccessFile("F:\\shar\\test\\test10.dat","rw");
        raf1.seek(3*DOUBLE_SIZE);  //找到某個位置
        raf1.writeDouble(300);     //往該位置插入數據
        raf1.seek(5*DOUBLE_SIZE);
        raf1.writeDouble(500);
        raf1.close();
        RandomAccessFile raf2 = new RandomAccessFile("F:\\shar\\test\\test10.dat","r");
        for (int i = 0; i < 10; i++) {
            System.out.print(" "+raf2.readDouble());
        }
        raf2.close();
    }

}