FileReader是用于读取字符流的类，它继承于InputStreamReader，要读取原始字节流，考虑使用FileInputStream；FileWriter是用于写入字符流的类，继承于OutputStreamWriter，要写入原始字节流，考虑使用FileOutputStream。
FileReader和FileWriter的示例代码：
public class FileReaderWriterTest {
private static final String FileName = "file.txt";
private static final String CharsetName = "utf-8";
public static void main(String[] args) {
testWrite();
testRead();
}
/**
* OutputStreamWriter 演示函数
*
*/
private static void testWrite() {
try {
// 创建文件“file.txt”对应File对象
File file = new File(FileName);
// 创建FileOutputStream对应FileWriter：将字节流转换为字符流，即写入out1的数据会自动由字节转换为字符。
FileWriter out1 = new FileWriter(file);
// 写入10个汉字
out1.write("字节流转为字符流示例");
// 向“文件中”写入"0123456789"+换行符
out1.write("0123456789\n");
out1.close();
} catch(IOException e) {
e.printStackTrace();
}
}
/**
* InputStreamReader 演示程序
*/
private static void testRead() {
try {
// 方法1：新建FileInputStream对象
// 新建文件“file.txt”对应File对象
File file = new File(FileName);
FileReader in1 = new FileReader(file);
// 测试read()，从中读取一个字符
char c1 = (char)in1.read();
System.out.println("c1="+c1);
// 测试skip(long byteCount)，跳过4个字符
in1.skip(6);
// 测试read(char[] cbuf, int off, int len)
char[] buf = new char[10];
in1.read(buf, 0, buf.length);
System.out.println("buf="+(new String(buf)));
in1.close();
} catch(IOException e) {
e.printStackTrace();
}
}
}运行结果：
c1=字
buf=流示例0123456
基于JDK8的FileReader的源代码：
public class FileReader extends InputStreamReader {
/**
* Creates a new <tt>FileReader</tt>, given the name of the
* file to read from.
*
* @param fileName the name of the file to read from
* @exception FileNotFoundException if the named file does not exist,
* is a directory rather than a regular file,
* or for some other reason cannot be opened for
* reading.
*/
public FileReader(String fileName) throws FileNotFoundException {
super(new FileInputStream(fileName));
}
/**
* Creates a new <tt>FileReader</tt>, given the <tt>File</tt>
* to read from.
*
* @param file the <tt>File</tt> to read from
* @exception FileNotFoundException if the file does not exist,
* is a directory rather than a regular file,
* or for some other reason cannot be opened for
* reading.
*/
public FileReader(File file) throws FileNotFoundException {
super(new FileInputStream(file));
}
/**
* Creates a new <tt>FileReader</tt>, given the
* <tt>FileDescriptor</tt> to read from.
*
* @param fd the FileDescriptor to read from
*/
public FileReader(FileDescriptor fd) {
super(new FileInputStream(fd));
}
}由源码分析得，FileReader继承于InputStreamReader，因此是使用的父类的操作。
基于JDK8 的FileWriter的源码分析：
public class FileWriter extends OutputStreamWriter {
/**
* Constructs a FileWriter object given a file name.
*
* @param fileName String The system-dependent filename.
* @throws IOException if the named file exists but is a directory rather
* than a regular file, does not exist but cannot be
* created, or cannot be opened for any other reason
*/
public FileWriter(String fileName) throws IOException {
super(new FileOutputStream(fileName));
}
/**
* Constructs a FileWriter object given a file name with a boolean
* indicating whether or not to append the data written.
*
* @param fileName String The system-dependent filename.
* @param append boolean if <code>true</code>, then data will be written
* to the end of the file rather than the beginning.
* @throws IOException if the named file exists but is a directory rather
* than a regular file, does not exist but cannot be
* created, or cannot be opened for any other reason
*/
public FileWriter(String fileName, boolean append) throws IOException {
super(new FileOutputStream(fileName, append));
}
/**
* Constructs a FileWriter object given a File object.
*
* @param file a File object to write to.
* @throws IOException if the file exists but is a directory rather than
* a regular file, does not exist but cannot be created,
* or cannot be opened for any other reason
*/
public FileWriter(File file) throws IOException {
super(new FileOutputStream(file));
}
/**
* Constructs a FileWriter object given a File object. If the second
* argument is <code>true</code>, then bytes will be written to the end
* of the file rather than the beginning.
*
* @param file a File object to write to
* @param append if <code>true</code>, then bytes will be written
* to the end of the file rather than the beginning
* @throws IOException if the file exists but is a directory rather than
* a regular file, does not exist but cannot be created,
* or cannot be opened for any other reason
* @since 1.4
*/
public FileWriter(File file, boolean append) throws IOException {
super(new FileOutputStream(file, append));
}
/**
* Constructs a FileWriter object associated with a file descriptor.
*
* @param fd FileDescriptor object to write to.
*/
public FileWriter(FileDescriptor fd) {
super(new FileOutputStream(fd));
}
}