package IO;import java.io.File;import java.io.FileNotFoundException;import java.io.IOException;import java.io.RandomAccessFile;public class TestRandomAccessFile { public static void main(String args[]) throws IOException { RandomAccessFile r = new RandomAccessFile //常见模式有r(读),rw(写) (new File("D:/java_foundation/src/IO/TestFile1.java"), "r"); r.seek(2); byte[] b = new byte[1024]; int len; while((len = r.read(b))!=-1) { System.out.println(new String(b,0,b.length)); } r.close(); }}有大佬知道 System.out.println(new String(b,0,b.length));与 System.out.println(new String(b,0,b.len));区别在哪，为什么如果用b. length有的不能输出吗