原因分析：

FileInputStream 的 read 方法實(shí)現(xiàn)如下：
可以看出，實(shí)際上調(diào)用了一個(gè)本地方法，每次讀取一個(gè)字節(jié)，都需要通過(guò) OS 來(lái)訪問(wèn)磁盤。

/**
 * Reads a byte of data from this input stream. This method blocks
 * if no input is yet available.
 *
 * @return     the next byte of data, or <code>-1</code> if the end of the
 *             file is reached.
 * @exception  IOException  if an I/O error occurs.
 */
public int read() throws IOException {
    return read0();
}

private native int read0() throws IOException;

BufferedInputStream 的 read 方法實(shí)現(xiàn)如下：
可以看出，BufferedInputStream 有一個(gè)緩沖區(qū)，每次從磁盤中讀取 8M 的字節(jié)，存儲(chǔ)到內(nèi)存緩沖區(qū)中，調(diào)用 read() 時(shí)實(shí)際上是讀取緩沖區(qū)，無(wú)需訪問(wèn)磁盤。

public synchronized int read() throws IOException {
    if (pos >= count) {
        fill();
        if (pos >= count)
            return -1;
    }
    return getBufIfOpen()[pos++] & 0xff;
}

讀取具體數(shù)據(jù)類型 DateInputStream & DateOutputStream

讀寫(xiě)格式：按字節(jié)讀寫(xiě)，按照具體的數(shù)據(jù)類型讀寫(xiě)特定數(shù)目的字節(jié)：

• readChar, writeChar：每次讀寫(xiě) 2 個(gè)字節(jié)

public final char readChar() throws IOException {
    int ch1 = in.read();
    int ch2 = in.read();
    if ((ch1 | ch2) < 0)
        throw new EOFException();
    return (char)((ch1 << 8) + (ch2 << 0));
}
public final void writeChar(int v) throws IOException {
    out.write((v >>> 8) & 0xFF);
    out.write((v >>> 0) & 0xFF);
    incCount(2);
}

• readInt, writeInt：每次讀寫(xiě) 4 個(gè)字節(jié)

public final int readInt() throws IOException {
    int ch1 = in.read();
    int ch2 = in.read();
    int ch3 = in.read();
    int ch4 = in.read();
    if ((ch1 | ch2 | ch3 | ch4) < 0)
        throw new EOFException();
    return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
}
public final void writeInt(int v) throws IOException {
    out.write((v >>> 24) & 0xFF);
    out.write((v >>> 16) & 0xFF);
    out.write((v >>>  8) & 0xFF);
    out.write((v >>>  0) & 0xFF);
    incCount(4);
}

• readDouble, writeDouble：每次讀寫(xiě) 8 個(gè)字節(jié)
• readLong, writeLong：每次讀寫(xiě) 8 個(gè)字節(jié)
• ...

DateInputStream & DateOutputStream 的使用：

public static void main(String[] args) throws Exception {
    OutputStream fout = new FileOutputStream("chars.txt");
    DataOutputStream dout = new DataOutputStream(fout);

    char chars[] = {'A', 'B', 'C', 'D'};
    for (int c : chars) {
        dout.writeChar(c);
    }
    dout.flush();

    InputStream fin = new FileInputStream("chars.txt");
    DataInputStream din = new DataInputStream(fin);
    char c;
    while (din.available() > 0) {
        c = din.readChar();
        System.out.print(c);
    }
}

輸出：

ABCD

注意事項(xiàng)：
如下代碼會(huì)將 1 按照二進(jìn)制形式寫(xiě)入文件中，占據(jù) 4 bytes。
因此用記事本打開(kāi)該文本文件，其實(shí)無(wú)法看到數(shù)字 1。

int i = 1;
dout.writeInt(i);

讀取對(duì)象 ObjectInputStream & ObjectOutputStream

讀寫(xiě)格式：按字節(jié)讀寫(xiě)，讀寫(xiě)的對(duì)象需要實(shí)現(xiàn) Serializable 接口。

ObjectInputStream & ObjectOutputStream 的使用：

public class Stream_Object_Test {

    public static void main(String[] args) throws Exception {
        OutputStream fout = new FileOutputStream("people.txt");
        ObjectOutputStream oout = new ObjectOutputStream(fout);

        People p = new People("Tom", 20);
        oout.writeObject(p);

        InputStream fin = new FileInputStream("people.txt");
        ObjectInputStream oin = new ObjectInputStream(fin);
        People new_p = (People) oin.readObject();
        System.out.println(new_p.getName() + " " + new_p.getAge());
    }
}

class People implements Serializable {
    private String name;
    private int age;

    People(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}