File
An abstract representation of file and directory pathnames.
public class File
extends Object
implements Serializable, Comparable<File>
//写txt文件也会被创建成文件夹并不会是txt文件
File file = new File("./src/cn/tju/scs/c02/file/test/test.txt");
txt文件是file不是directory
文件夹是directory不是file
file分hidden不hidden，isFile()用于判断是不是normal file
Stream
public interface Stream<T>
extends BaseStream<T,Stream<T>>
//In this example, widgets is a Collection<Widget>.
//We create a stream of Widget objects via Collection.stream(),
//filter it to produce a stream containing only the red widgets,
//then transform it into a stream of int values representing the weight of each red widget.
//Then this stream is summed to produce a total weight.
int sum = widgets.stream()
.filter(w -> w.getColor() == RED)
.mapToInt(w -> w.getWeight())
.sum();
可以represent多种source和destination（disk file，device，programs，memory arrays等）
支持多种格式的数据（最简单的bytes，八种基本数据类型，objects，虽然其中有一些会改变data格式）
– A program uses an input stream to read data from a source– A program uses an output stream to write data to a destination
Java.io包中定义流的分类
方式一：数据流的方向：
InputStream
是抽象类，需要用其子类 that returns the next byte of input.
public abstract class InputStream
extends Object //并不是Stream的子类，也没有实现Stream接口
implements Closeable//只有一个void方法 close()
//主要方法
public abstract int read()
throws IOException
//父类指针指向子类对象
OutputStream os = new FileOutputStream(file, true)
OutputStream
An output stream accepts output bytes and sends them to some sink.
是抽象类，需要其子类来写入文件，或者写到其他地方
public abstract class OutputStream
extends Object
implements Closeable, Flushable
//没有无参的write
public abstract void write(int b)
throws IOException
//If the second argument is true, then bytes will be written to the end of the file rather than the beginning.
FileOutputStream(File file, boolean append)
throws FileNotFoundException
close();
方式二：处理数据的单位：
Byte Stream （字节流）和 Character Stream（字符流）
InputStream OutputStream Reader Writer是java.io包里的四个抽象类
其中，
InputStream和OutputStream属于按字节流处理数据
Reader和Writer属于按字符流处理数据
OutputStream需要close()
Writer不需要，但可以flush()
开发中字节数据比较多，图片、音乐、电影
字符最大的好处，中文的有效处理，如果处理中文，优先使用字符流，除此之外，以字节流为主。
public abstract class Reader
extends Object
implements Readable, Closeable
public int read()
throws IOException//也抛出IO异常
//Abstract class for reading character streams.
//The only methods that a subclass must implement are read(char[], int, int) and close().
public abstract class Writer
extends Object
//Flushable只有一个方法 void flush() throws IOException
implements Appendable, Closeable, Flushable
PrintStream & PrintWriter
字符打印流 & 字节打印流
public class PrintStream
extends FilterOutputStream
implements Appendable, Closeable
//outputStream只能输出以字节类型为主的数据
//int(Integer)、double(Double)、Date类型 的输出由PrintStream输出
PrintStream(OutputStream out);
public void print(数据类型 参数名称);
整数(%d)、字符串(%s)、小数(%m.nf)、字符(%c)。
System.in
try{
Integer.parseInt("abc");
} catch(Exception e){
//结果相同，err为红色
System.err.println(e);
System.out.println(e);
}
printf()返回类型是PrintStream
print() println() 返回类型是void
