Java InputStream 和DataInputStrea

1. DataInputStream 继承于FilterInputStream ，FilterInputStream继承于InputStream。因此可以说InputSteam是DataInputStream的父类。
2. DataInputStream 实现了 DataInput的接口。
   重载了以下方法（并设置为final）：

public interface DataInput {
    void readFully(byte[] var1) throws IOException;

    void readFully(byte[] var1, int var2, int var3) throws IOException;

    int skipBytes(int var1) throws IOException;

    boolean readBoolean() throws IOException;

    byte readByte() throws IOException;

    int readUnsignedByte() throws IOException;

    short readShort() throws IOException;

    int readUnsignedShort() throws IOException;

    char readChar() throws IOException;

    int readInt() throws IOException;

    long readLong() throws IOException;

    float readFloat() throws IOException;

    double readDouble() throws IOException;

    String readLine() throws IOException;

    String readUTF() throws IOException;
}

3. DataInputStream 重载了FilterInputStream 部分的方法，并设置为final 类型方法，可以继承DataInputStream 类，但是无法重载父类方法。
   DataInputStream 方法：

public class DataInputStream extends FilterInputStream implements DataInput {
    public DataInputStream(InputStream in) {
        super((InputStream)null);
        throw new RuntimeException("Stub!");
    }

    public final int read(byte[] b) throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final int read(byte[] b, int off, int len) throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final void readFully(byte[] b) throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final void readFully(byte[] b, int off, int len) throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final int skipBytes(int n) throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final boolean readBoolean() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final byte readByte() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final int readUnsignedByte() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final short readShort() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final int readUnsignedShort() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final char readChar() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final int readInt() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final long readLong() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final float readFloat() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final double readDouble() throws IOException {
        throw new RuntimeException("Stub!");
    }

    /** @deprecated */
    @Deprecated
    public final String readLine() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public final String readUTF() throws IOException {
        throw new RuntimeException("Stub!");
    }

    public static final String readUTF(DataInput in) throws IOException {
        throw new RuntimeException("Stub!");
    }
}

4. DataInputStream （数据输入流）允许应用程序以与机器无关方式从底层输入流中读取基本 Java 数据类型。
   下面的构造方法用来创建数据输入流对象。

DataInputStream dis = new DataInputStream(InputStream in);

方法描述：

5. 实例

下面的例子演示了DataInputStream和DataOutputStream的使用，该例从文本文件test.txt中读取5行，并转换成大写字母，最后保存在另一个文件test1.txt中。
test.tx 文件内容如下：

代码：

import java.io.*;
 
public class Test{
   public static void main(String args[])throws IOException{
 
      DataInputStream in = new DataInputStream(new FileInputStream("test.txt"));
      DataOutputStream out = new DataOutputStream(new  FileOutputStream("test1.txt"));
      BufferedReader d  = new BufferedReader(new InputStreamReader(in));
     
      String count;
      while((count = d.readLine()) != null){
          String u = count.toUpperCase();
          System.out.println(u);
          out.writeBytes(u + "  ,");
      }
      d.close();
      out.close();
   }
}

6. 通过实例可以看出流程：

• 创建InputStream对象（所有InputStream的子类对象，可以是文件输入流等）。
• 创建DataInputStream 对象，构造参数为 InputStream 对象
• 创建 InputStreamReader 对象，构造参数为DataInputStream 对象
• 创建 BufferedReader 对象，构造参数为 InputStreamReader 对象
• 最终通过BufferedReader 对象来操作 文件输入流 数据。