PrintErrorAndNextLine

public class Solution {
  public static void main(String []argv) {
    BufferedReader br = new BufferedReader(new FileReader("...."));
    
    boolean prevHasError = false;
    int lineNum = 0;
    while (br.hasNext()) {
      String line = br.readLine();
      boolean hasError = (line.indexOf("error") != -1);
      if (hasError || prevHasError) {
        System.out.println(lineNum + " " + line);
      }
      prevHasError = hasError;
      lineNum++;
    }
  }
}