基于bufferedreader的read()与readline()读取出错原因及解决

int c; 
FileReader file = new FileReader("D:\\emDemo.java");
   BufferedReader br = new BufferedReader(file);
   while((c=br.read())!=-1){undefined
    System.out.println(br.readLine());
   }

String input = null;
   while ((input=br.readLine())!=null){undefined
    System.out.println(input);
   }

String readLine(boolean ignoreLF) throws ioException {
		//行（hang）数据的缓冲s
		StringBuffer s = null;
		int startChar;
 
	        synchronized (lock) {
	       
	            ensureOpen();
	            
	          
		    boolean omitLF = ignoreLF || skipLF;
 
		 	
		    bufferLoop:
		    for (;;) {
		    	
		    	//1、如果缓冲数组的数据不足，或者已经读到了数组的末尾时：
		    	//1.1如果下次读取的位置已经到了or超过数组的长度，从流中读数据到缓冲数组cb中
			if (nextChar >= nChars)
			    fill();
			
			if (nextChar >= nChars) { 
			    if (s != null && s.length() > 0)
				return s.toString();
			    else
				return null;
			}
			
			
			//2 缓冲数组中有足够的数据时：
			
			boolean eol = false;
			char c = 0;
			int i;
 
			if (omitLF && (cb[nextChar] == '\n')) 
	                    nextChar++;
			skipLF = false;
			omitLF = false;
 
		    charLoop:
			for (i = nextChar; i < nChars; i++) {
			    c = cb[i];
			    if ((c == '\n') || (c == '\r')) {
				eol = true;
				break charLoop;
			    }
			}
			
			
			startChar = nextChar;
			nextChar = i;
			if (eol) {
			    String str;
			    
			    if (s == null)
			    {
				str = new String(cb, startChar, i - startChar);
			    } 
			    
			    else
			    {
				s.append(cb, startChar, i - startChar);
				str = s.toString();
			    }
			  //更新下次读取的位置
			    nextChar++;
			    if (c == '\r') {
				skipLF = true;
			    }
			    return str;
			}
			//2.2如果没有换行符
			if (s == null) 
				//类属性int defaultExpectedLineLength = 80
			    s = new StringBuffer(defaultExpectedLineLength);
			//填充s，从上个换行符到最后
			s.append(cb, startChar, i - startChar);
		    }
	        }
	    }