二、缓冲区

提高了对数据的读写效率。

对应类：

BufferedWriter

BufferedReader

1、缓冲区单个字符读写

public class Demo6 {

    public static void main(String[] args) throws IOException {
        FileReader fr = new FileReader("demo.txt");
        BufferedReader bufr = new BufferedReader(fr);

        FileWriter fw = new FileWriter("buf_copy.txt");
        BufferedWriter bufw = new BufferedWriter(fw);

        int ch = 0;
        while((ch = bufr.read())!=-1) {
            bufw.write(ch);
        }
        bufw.close();
        bufr.close();

    }

}

2、缓冲区逐行读写

public class Demo6 {

    public static void main(String[] args) throws IOException {
        FileReader fr = new FileReader("demo.txt");
        BufferedReader bufr = new BufferedReader(fr);

        FileWriter fw = new FileWriter("buf_copy.txt");
        BufferedWriter bufw = new BufferedWriter(fw);

        String line = null;

        while((line = bufr.readLine())!=null) {
            bufw.write(line);
            bufw.newLine();
            bufw.flush();
        }

        bufw.close();
        bufr.close();

    }

}

3、缓冲区 - 装饰设计模式

装饰设计模式：

对一组对象的功能进行增强时，就可以使用该模式解决问题。

public class Person {
    public void eat() {
        System.out.println("....eating...");
    }
}

//通过继承进行功能扩展
class NewPerson extends Person{
    public void eat() {
        System.out.println("befor...eating...");
        super.eat();
        System.out.println("after...eating");
    }
}

//通过装饰类进行功能扩展
class NewPerson2 {
    private Person p;
    NewPerson2(Person p){
        this.p = p;
    }
    void eat() {        
        System.out.println("befor...eating...");
        p.eat();
        System.out.println("after...eating");
    }
}

装饰和继承的区别：

Writer

|– TextWriter:用于操作文本

—– BufferedTextWriter:加入缓冲技术

|– MediaWriter:用于操作媒体

—– BufferedMediaWriter:加入缓冲技术

继承导致原有类的体系越来越臃肿，不够灵活。

class Buffered {
Buffered(Writer w){
…
}
}

装饰比继承更灵活。

4、缓冲区 - 装饰类 - LineNumberReader

public class Demo7 {

    public static void main(String[] args) throws IOException {

        FileReader fr = new FileReader("demo.txt");
        LineNumberReader lnr = new LineNumberReader(fr);

        String line = null;
        lnr.setLineNumber(100);
        while((line = lnr.readLine()) != null) {
            System.out.println(lnr.getLineNumber()+":"+line);
        }
    }

}

输出结果：
101:abc
102:cde