代码如下：
public class MyBufferedReader {
public FileReader reader = null;
public MyBufferedReader(FileReader reader){
  this.reader = reader;
}
public String myReadLine() throws IOException{//定义要功能抛出异常
  StringBuilder sb = new StringBuilder();
  char b = 0;
  while((b= (char) reader.read())!=-1){
   if(b=='\r')
    continue;
   if(b=='\n')
    return sb.toString();
   else{
   sb.append((char)b);//栈溢出
   }
   
  }

  if(sb.length()!=0)
   return sb.toString();
  return null;
  
}
public void Myclose() throws IOException {
  reader.close();
  
}


}
class MyBufferedTest{
public static void main(String[] args){
  MyBufferedReader buf = null;
  try {
   buf = new MyBufferedReader(new FileReader("buf.txt"));
   String len = null;
   while((len=buf.myReadLine())!=null){
    System.out.println(len);
   }
  } catch (FileNotFoundException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }finally{
   try {
    if(buf!=null)
    buf.Myclose();
   } catch (IOException e) {
    // TODO Auto-generated catch block
    throw new RuntimeException("读取关闭失败");
   }
  }
}
}

报错：
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:2882)
at java.lang.AbstractStringBuilder.expandCapacity(AbstractStringBuilder.java:100)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:572)
at java.lang.StringBuilder.append(StringBuilder.java:203)
at cn.itcast.io.MyBufferedReader.myReadLine(MyBufferedReader.java:22)
at cn.itcast.io.MyBufferedTest.main(MyBufferedReader.java:45)

char b = 0;
你把b的类型定义成char类型，
然后 while((b= (char) reader.read())!=-1){
你把reader.read()返回值强转化成char 再与-1进行比较，这肯定不会相等嘛。
while死循环，sb.append((char)b一直在执行，所以会出现OutOfMemoryError

刚回错了，再研究一下

1. import java.io.FileNotFoundException;
   
2. import java.io.FileReader;
   
3. import java.io.IOException;
   
4. 
   
5. class MyBufferedReader1 {
   
6. public FileReader reader = null;
   
7. public MyBufferedReader1(FileReader reader){
   
8.   this.reader = reader;
   
9. }
   
10. public String myReadLine() throws IOException{//定义要功能抛出异常
    
11.   StringBuilder sb = new StringBuilder();
    
12.   
    
13.    int b = 0;
    
14.   while((b=reader.read())!=-1){
    
15.    if(b=='\r')
    
16.     continue;
    
17.    if(b=='\n')
    
18.     return sb.toString();
    
19.    else{
    
20.    sb.append((char)b);//栈溢出
    
21.    }
    
22.    
    
23.   }
    
24. 
    
25.   if(sb.length()!=0)
    
26.    return sb.toString();
    
27.   return null;
    
28.   
    
29. }
    
30. public void Myclose() throws IOException {
    
31.   reader.close();
    
32.   
    
33. }
    
34. 
    
35. 
    
36. }
    
37. public class aa{
    
38. public static void main(String[] args){
    
39.   MyBufferedReader1 buf = null;
    
40.   try {
    
41.    buf = new MyBufferedReader1(new FileReader("F:\\zz.txt"));
    
42.    String len = null;
    
43.    while((len=buf.myReadLine())!=null){
    
44.     System.out.println(len);
    
45.    }
    
46.   } catch (FileNotFoundException e) {
    
47.    // TODO Auto-generated catch block
    
48.    e.printStackTrace();
    
49.   } catch (IOException e) {
    
50.    // TODO Auto-generated catch block
    
51.    e.printStackTrace();
    
52.   }finally{
    
53.    try {
    
54.     if(buf!=null)
    
55.     buf.Myclose();
    
56.    } catch (IOException e) {
    
57.     // TODO Auto-generated catch block
    
58.     throw new RuntimeException("读取关闭失败");
    
59.    }
    
60.   }
    
61. }
    
62. }

复制代码

reader.read()返回的是一个int型数据，然后再与-1进行比较；我把你的b类型改成int；MyBufferedReader 前面的public去掉，MyBufferedTest前面加上public就没有问题了

顶！{:soso_e100:}