Revise the threaded sort application to improve the performance by applying one or more of the principles to improve the efficiency of I/O.
Provide the improved code.
Here is the code:
public class MergeSort { // The mergeSort method returns a sorted copy of the // String objects contained in the String array data. /** * Sorts the String objects using the merge sort algorithm. * * @param data the String objects to be sorted * @return the String objects sorted in ascending order */ public static String[] mergeSort(String[] data) {
if (data.length > 1) { String[] left = new String[data.length / 2]; String[] right = new String[data.length – left.length]; System.arraycopy(data, 0, left, 0, left.length); System.arraycopy(data, left.length, right, 0, right.length); left = mergeSort(left); right = mergeSort(right); return merge(left, right); } else { return data; } } /** * The merge method accepts two String arrays that are assumed * to be sorted in ascending order. The method will return a * sorted array of String objects containing all String objects * from the two input collections. * * @param left a sorted collection of String objects * @param right a sorted collection of String objects * @return a sorted collection of String objects */ public static String[] merge(String[] left, String[] right) { String[] data = new String[left.length + right.length]; int lIndex = 0; int rIndex = 0; for (int i=0; i<data.length; i++) { if (lIndex == left.length) { data[i] = right[rIndex]; rIndex++; } else if (rIndex == right.length) { data[i] = left[lIndex]; lIndex++; } else if (left[lIndex].compareTo(right[rIndex]) < 0) { data[i] = left[lIndex]; lIndex++; } else { data[i] = right[rIndex]; rIndex++; } } return data; } }Sort.java:
import java.io.BufferedReader;import java.io.File;import java.io.FileReader;import java.io.IOException;import java.util.ArrayList;
public class Sort {
/** * You are to implement this method. The method should invoke one or * more threads to read and sort the data from the collection of Files. * The method should return a sorted list of all of the String data * contained in the files. * * @param files * @return * @throws IOException */ public static void threadedSort(File[] files) throws IOException { //Commenting out to use the multithread /* throw new java.lang.IllegalStateException(“Method not implemented”); */ } /** * Given an array of files, this method will return a sorted * list of the String data contained in each of the files. * * @param files the files to be read * @return the sorted data * @throws IOException thrown if any errors occur reading the file */ public static String[] sort(File[] files) throws IOException {
String[] sortedData = new String[0];
for (File file : files) { String[] data = getData(file); data = MergeSort.mergeSort(data); sortedData = MergeSort.merge(sortedData, data); }
return sortedData;
}
/** * This method will read in the string data from the specified * file and return the data as an array of String objects. * * @param file the file containing the String data * @return String array containing the String data * @throws IOException thrown if any errors occur reading the file */ private static String[] getData(File file) throws IOException {
ArrayList<String> data = new ArrayList<String>(); BufferedReader in = new BufferedReader(new FileReader(file));
// Read the data from the file until the end of file is reached while (true) { String line = in.readLine(); if (line == null) { // the end of file was reached break; } else { data.add(line); } } //Close the input stream and return the data in.close(); return data.toArray(new String[0]);
}}
SortTest:
import java.io.File;import java.io.IOException;
/** * The class SortTest is used to test the threaded and non-threaded * sort methods. This program will call each method to sort the data * contained in the four test files. This program will then test the * results to ensure that the results are sorted in ascending order. * * Simply run this program to verify that you have correctly implemented * the threaded sort method. The program will not verify if your sort * uses threads, but will verify if your implementation correctly * sorted the data contained in the four files. * * There should be no reason to make modifications to this class. */public class SortTest { public static void main(String[] args) throws IOException { File[] files = {new File(“enable1.txt”), new File(“enable2k.txt”), new File(“lower.txt”), new File(“mixed.txt”)};
// Run Sort.sort on the files long startTime = System.nanoTime(); String[] sortedData = Sort.sort(files); long stopTime = System.nanoTime(); double elapsedTime = (stopTime – startTime) / 1000000000.0; // Test to ensure the data is sorted for (int i=0; i<sortedData.length-1; i++) { if (sortedData[i].compareTo(sortedData[i+1]) > 0) { System.out.println(“The data returned by Sort.sort is not sorted.”); throw new java.lang.IllegalStateException(“The data returned by Sort.sort is not sorted”); } } System.out.println(“The data returned by Sort.sort is sorted.”); System.out.println(“Sort.sort took ” + elapsedTime + ” seconds to read and sort the data.”); // Run Sort.threadedSort on the files and test to ensure the data is sorted startTime = System.nanoTime(); // Commenting out /*String[] threadSortedData = Sort.threadedSort(files); stopTime = System.nanoTime(); double threadedElapsedTime = (stopTime – startTime)/ 1000000000.0; // Test to ensure the data is sorted if (sortedData.length != threadSortedData.length) { System.out.println(“The data return by Sort.threadedSort is missing data”); throw new java.lang.IllegalStateException(“The data returned by Sort.threadedSort is not sorted”); } for (int i=0; i<threadSortedData.length-1; i++) { if (threadSortedData[i].compareTo(threadSortedData[i+1]) > 0) { System.out.println(“The data return by Sort.threadedSort is not sorted”); throw new java.lang.IllegalStateException(“The data returned by Sort.threadedSort is not sorted”); } } System.out.println(“The data returned by Sort.threadedSort is sorted.”); System.out.println(“Sort.threadedSort took ” + threadedElapsedTime + ” seconds to read and sort the data.”); } } */
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