Add Java implementation of COBOL merge sort with file-based operations

merge_sort/CustomerRecord.java

@@ -0,0 +1,87 @@
+public class CustomerRecord {
+    private int customerId;
+    private String lastName;
+    private String firstName;
+    private int contractId;
+    private String comment;
+
+    public CustomerRecord(int customerId, String lastName, String firstName, int contractId, String comment) {
+        this.customerId = customerId;
+        this.lastName = lastName;
+        this.firstName = firstName;
+        this.contractId = contractId;
+        this.comment = comment;
+    }
+
+    public int getCustomerId() {
+        return customerId;
+    }
+
+    public void setCustomerId(int customerId) {
+        this.customerId = customerId;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public int getContractId() {
+        return contractId;
+    }
+
+    public void setContractId(int contractId) {
+        this.contractId = contractId;
+    }
+
+    public String getComment() {
+        return comment;
+    }
+
+    public void setComment(String comment) {
+        this.comment = comment;
+    }
+
+    public String toFixedWidthString() {
+        return String.format("%05d%-50s%-50s%05d%-25s",
+            customerId,
+            lastName,
+            firstName,
+            contractId,
+            comment);
+    }
+
+    public String toDisplayString() {
+        return String.format("%05d%-50s%-50s%05d%-25s",
+            customerId,
+            lastName,
+            firstName,
+            contractId,
+            comment);
+    }
+
+    public static CustomerRecord fromFixedWidthString(String line) {
+        if (line.length() < 135) {
+            return null;
+        }
+
+        int customerId = Integer.parseInt(line.substring(0, 5));
+        String lastName = line.substring(5, 55).trim();
+        String firstName = line.substring(55, 105).trim();
+        int contractId = Integer.parseInt(line.substring(105, 110));
+        String comment = line.substring(110, 135).trim();
+
+        return new CustomerRecord(customerId, lastName, firstName, contractId, comment);
+    }
+}

merge_sort/MergeSortExample.java

@@ -0,0 +1,102 @@
+import java.io.*;
+import java.util.*;
+
+public class MergeSortExample {
+
+    public static void main(String[] args) {
+        MergeSortExample example = new MergeSortExample();
+
+        example.createTestData();
+        example.mergeAndDisplayFiles();
+        example.sortAndDisplayFile();
+
+        System.out.println("Done.");
+    }
+
+    public void createTestData() {
+        System.out.println("Creating test data files...");
+
+        List<CustomerRecord> file1Records = Arrays.asList(
+            new CustomerRecord(1, "last-1", "first-1", 5423, "comment-1"),
+            new CustomerRecord(5, "last-5", "first-5", 12323, "comment-5"),
+            new CustomerRecord(10, "last-10", "first-10", 653, "comment-10"),
+            new CustomerRecord(50, "last-50", "first-50", 5050, "comment-50"),
+            new CustomerRecord(25, "last-25", "first-25", 7725, "comment-25"),
+            new CustomerRecord(75, "last-75", "first-75", 1175, "comment-75")
+        );
+
+        List<CustomerRecord> file2Records = Arrays.asList(
+            new CustomerRecord(999, "last-999", "first-999", 1610, "comment-99"),
+            new CustomerRecord(3, "last-03", "first-03", 3331, "comment-03"),
+            new CustomerRecord(30, "last-30", "first-30", 8765, "comment-30"),
+            new CustomerRecord(85, "last-85", "first-85", 4567, "comment-85"),
+            new CustomerRecord(24, "last-24", "first-24", 247, "comment-24")
+        );
+
+        writeRecordsToFile("test-file-1.txt", file1Records);
+        writeRecordsToFile("test-file-2.txt", file2Records);
+    }
+
+    public void mergeAndDisplayFiles() {
+        System.out.println("Merging and sorting files...");
+
+        List<CustomerRecord> file1Records = readRecordsFromFile("test-file-1.txt");
+        List<CustomerRecord> file2Records = readRecordsFromFile("test-file-2.txt");
+
+        List<CustomerRecord> allRecords = new ArrayList<>();
+        allRecords.addAll(file1Records);
+        allRecords.addAll(file2Records);
+
+        allRecords.sort(Comparator.comparingInt(CustomerRecord::getCustomerId));
+
+        for (CustomerRecord record : allRecords) {
+            System.out.println(record.toDisplayString());
+        }
+
+        writeRecordsToFile("merge-output.txt", allRecords);
+    }
+
+    public void sortAndDisplayFile() {
+        System.out.println("Sorting merged file on descending contract id....");
+
+        List<CustomerRecord> records = readRecordsFromFile("merge-output.txt");
+
+        records.sort(Comparator.comparingInt(CustomerRecord::getContractId).reversed());
+
+        for (CustomerRecord record : records) {
+            System.out.println(record.toDisplayString());
+        }
+
+        writeRecordsToFile("sorted-contract-id.txt", records);
+    }
+
+    private void writeRecordsToFile(String filename, List<CustomerRecord> records) {
+        try (PrintWriter writer = new PrintWriter(new FileWriter(filename))) {
+            for (CustomerRecord record : records) {
+                writer.println(record.toFixedWidthString());
+            }
+        } catch (IOException e) {
+            System.err.println("Error writing to file " + filename + ": " + e.getMessage());
+        }
+    }
+
+    private List<CustomerRecord> readRecordsFromFile(String filename) {
+        List<CustomerRecord> records = new ArrayList<>();
+
+        try (BufferedReader reader = new BufferedReader(new FileReader(filename))) {
+            String line;
+            while ((line = reader.readLine()) != null) {
+                if (!line.trim().isEmpty()) {
+                    CustomerRecord record = CustomerRecord.fromFixedWidthString(line);
+                    if (record != null) {
+                        records.add(record);
+                    }
+                }
+            }
+        } catch (IOException e) {
+            System.err.println("Error reading from file " + filename + ": " + e.getMessage());
+        }
+
+        return records;
+    }
+}