binary search tree java

import java.io.BufferedReader; import java.io.IOException; import java.nio.file.Files; import java.nio.file.Path; import java.nio.file.Paths; public class Main { public static final String DEFAULT_TRAINING_FILENAME = "GreenEggsAndHam.txt"; public static final int CUTOFF_FREQUENCY = 15; public static final int MIN_PREFIX_LEN = 1; public static final int MAX_PREFIX_LEN = 5; public static final boolean USE_FREQ_LIST = false; public static final int[] FREQ_LIST = {35, 25, 15, 10, 5}; public static void main(String[] args) { String fileData = getFileData(DEFAULT_TRAINING_FILENAME); FrequencyFilter filt = new FrequencyFilter(); filt.buildFrequencyTrees(fileData, MIN_PREFIX_LEN, MAX_PREFIX_LEN); if (USE_FREQ_LIST) { System.out.println(filt.filter(FREQ_LIST)); } else { System.out.println(filt.filter(CUTOFF_FREQUENCY)); } } private static String getFileData(String filename) { Path trainingFilePath = Paths.get(filename); BufferedReader reader = null; try { reader = Files.newBufferedReader(trainingFilePath); } catch (IOException e) { System.err.println(e); System.exit(-1); } StringBuilder fileContents = readFile(reader); try { reader.close(); } catch (IOException e) { System.err.println("An error occurred while closing the file"); System.exit(-1); } if (fileContents == null) { System.exit(-1); } fileContents = sanitizeFileContents(fileContents); return fileContents.toString().trim(); } private static StringBuilder readFile(BufferedReader fileReader) { StringBuilder fileContents = new StringBuilder(); try { String line = null; while ((line = fileReader.readLine()) != null) { fileContents.append(line.trim() + " "); } } catch (IOException e) { System.err.println(e); System.err.println("An error occurred while reading from the file"); return null; } return fileContents; } private static StringBuilder sanitizeFileContents(StringBuilder fileContents) { String[] words = fileContents.toString().split("\\s"); StringBuilder sanitizedFileContents = new StringBuilder(fileContents.length()); for (String word : words) { if (word.isEmpty() || word.trim().isEmpty()) { continue; } sanitizedFileContents.append(word + " "); } return sanitizedFileContents; } }