JAVA自学教程之 IO流（四）转换流。
一、键盘录入
System.out:标准输出设备，控制台
System.in：标准输入设备，键盘
输入演示
输入字符串遇到回车，打印，输入over，输入结束
PS:键盘的录入只读取一个字节，先将字节拼一个字符串，所以需要一个容器，再参与over的判断
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import java.io.*;
public class Main
{
public static void main(String[] args) throws IOException {
InputStream in = System.in;
StringBuilder sb = new StringBuilder();
int t = 0;
while(true){
t = in.read();Windows下回车是’\r\n’
if(t== 13)continue;//’\r’ = 13
if(t==10){//’\n’ = 10
String str = sb.toString();
if(str.equals(“over”))
break;
System.out.println(str);
sb.delete(0, sb.length());//注意情况，否则字符串会越来越长
}
else {
sb.append((char)t);
}
}
System.out.println(t);
}
}
read():是阻塞式方法，没数据就一直等待
注意：默认的输入输出设备不要关，一旦关闭，以后再也无法创建流对象了
二、转换流
因为有readLine()方法，就不必要一个字符一个字符的读取，这就涉及到了字符流转换到字符流
在Reader类中有一个InputStreamReader()类，用来转换字节与字符
API文档解释：InputStreamReader是字节流通向字符流的桥梁：它使用指定的charset 读取字节并将其解码为字符。
而字符流的由来：字符流+编码表
字节流转字符流
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import java.io.*;
public class Main
{
public static void main(String[] args) throws IOException {
InDemo();
}
public static void InDemo() throws IOException{
InputStream in = System.in;//字节流
InputStreamReader ins = new InputStreamReader(in);//转换字符流
BufferedReader br = new BufferedReader(ins);//缓冲区，增强
String str = null;
while((str = br.readLine())!=null){
if(str.equals(“over”))break;
System.out.println(str);
}
}
}
字符流转字节流
在Writer类下有OuputStreamWriter类
API文档解释：OutputStreamWriter是字符流通向字节流的桥梁：可使用指定的charset 将要写入流中的字符编码成字节。
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import java.io.*;
public class Main
{
private static String LINE_SEPARATOR = System.getProperty(“line.separator”);
public static void main(String[] args) throws IOException {
InDemo();
}
public static void InDemo() throws IOException{
/*InputStream in = System.in;//字节流
InputStreamReader ins = new InputStreamReader(in);//转换字符流
BufferedReader br = new BufferedReader(ins);*/
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
/*OutputStream out = System.out;//标准输出流
OutputStreamWriter osw = new OutputStreamWriter(out);
BufferedWriter bw = new BufferedWriter(osw);*/
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
String str = null;
while((str = br.readLine())!=null){
if(str.equals(“over”))break;
//将字符数据用缓冲区对象写入缓冲区中，最终目的地osw->out->控制台
bw.write(str+LINE_SEPARATOR);
bw.flush();
}
}
}
三、转换流演示
将数据写到文本文件中
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import java.io.*;
public class Main
{
private static String LINE_SEPARATOR = System.getProperty(“line.separator”);
public static void main(String[] args) throws IOException {
InDemo();
}
public static void InDemo() throws IOException{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(“acm.txt”)));
String str = null;
while((str = br.readLine())!=null){
if(str.equals(“over”))break;
bw.write(str+LINE_SEPARATOR);
bw.flush();
}
}
}
将一个文本文件显示到控制台
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import java.io.*;
public class Main
{
private static String LINE_SEPARATOR = System.getProperty(“line.separator”);
public static void main(String[] args) throws IOException {
InDemo();
}
public static void InDemo() throws IOException{
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(“acm.txt”)));
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
String str = null;
while((str = br.readLine())!=null){
if(str.equals(“over”))break;
bw.write(str+LINE_SEPARATOR);
bw.flush();
}
}
}
将一个文件的内容复制到另一个文件中
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import java.io.*;
public class Main
{
private static String LINE_SEPARATOR = System.getProperty(“line.separator”);
public static void main(String[] args) throws IOException {
InDemo();
}
public static void InDemo() throws IOException{
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(“acm.txt”)));
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(“A.txt”)));
String str = null;
while((str = br.readLine())!=null){
if(str.equals(“over”))break;
bw.write(str+LINE_SEPARATOR);
bw.flush();
}
}
}
上述三个例子，改变的只是流的源和目的地