未插入新行

System.getProperty(\"line.separator\")

import java.io.FileOutputStream;
public class Find {
    public static void main(String args[]) {
        try {
            String s1=new String(\"127.0.0.1 www.google.com127.0.0.1 www.bing.com\");
            String s2=new String(\"127.0.0.1 www.google.com\" + \"\\n\" +
                \"127.0.0.1 www.bing.com\");

            byte buffer1[]=s1.getBytes();
            byte buffer2[]=s2.getBytes();

            FileOutputStream fos=new FileOutputStream(\"f1.txt\");
            for(int i=0;i<buffer1.length;i++)
                fos.write(buffer1[i]);

            FileOutputStream fos2=new FileOutputStream(\"f2.txt\");
            for(int i=0;i<buffer2.length;i++)
                fos2.write(buffer2[i]);

            System.out.println(\"size of buffer1 = \"+buffer1.length);
            System.out.println(\"size of buffer2 = \"+buffer2.length);

            String x=new String(\"s\"+\"\\n\"+\"u\");
            System.out.println(x);
        } catch (Exception e) {}
    }
}

size of buffer1 = 46
size of buffer2 = 47
s
u

f1.txt:
    127.0.0.1 www.google.com127.0.0.1 www.bing.com
f2.txt:
    127.0.0.1 www.google.com
    127.0.0.1 www.bing.com

line.separator

\\n

\\r\\n

String s2=new String(\"127.0.0.1 www.google.com\" +
    System.getProperty(\"line.separator\") +
    \"127.0.0.1 www.bing.com\");

FileOutputStream f = new FileOutputStream(\"f2.txt\");
PrintStream ps = new PrintStream(f);
ps.print(\"127.0.0.1 www.google.com\");
ps.println(); //this writes your new line
ps.print(\"127.0.0.1 www.bing.com\");
ps.close();