Java读取中间文本文件实现分组列数据求和及百分比计算的问题求助

I've run into this exact issue before with fixed-width formatted files converted to space-separated lines—those variable spaces are a real pain! Let's fix this step by step, starting with the parsing problem and then building out the grouped sum and percentage calculation.

Here's a complete, working solution that addresses your whitespace parsing issue, handles state-wise grouping, and computes the required percentages:

import java.io.*;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

// Custom class to hold aggregated data for each state
class StateAggregate {
    int totalPopulation;
    int schoolAgeChildren;
    int povertyChildren;

    public StateAggregate() {
        this.totalPopulation = 0;
        this.schoolAgeChildren = 0;
        this.povertyChildren = 0;
    }

    public void add(int total, int schoolAge, int poverty) {
        this.totalPopulation += total;
        this.schoolAgeChildren += schoolAge;
        this.povertyChildren += poverty;
    }
}

public class StatePopulationAnalyzer {
    public static void main(String[] args) {
        // Map to hold aggregated data per state code
        Map<String, StateAggregate> stateDataMap = new HashMap<>();

        try (BufferedReader reader = new BufferedReader(new FileReader("IntermediateSmallAreaIncomePovertyEstData.txt"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                // Use Scanner to handle variable whitespace automatically
                Scanner lineScanner = new Scanner(line);
                String stateCode = lineScanner.next();
                int totalPop = lineScanner.nextInt();
                int schoolAge = lineScanner.nextInt();
                int poverty = lineScanner.nextInt();

                // Get or create the aggregate entry for this state
                StateAggregate aggregate = stateDataMap.getOrDefault(stateCode, new StateAggregate());
                aggregate.add(totalPop, schoolAge, poverty);
                stateDataMap.put(stateCode, aggregate);
            }

            // Print formatted results
            System.out.printf("%-10s %-15s %-20s %-25s %-20s\n", 
                    "State Code", "Total Population", "School Age Children", "Poverty Children", "% Poverty (School Age)");
            System.out.println("--------------------------------------------------------------------------------------------------------");
            for (Map.Entry<String, StateAggregate> entry : stateDataMap.entrySet()) {
                String stateCode = entry.getKey();
                StateAggregate data = entry.getValue();
                // Calculate percentage, handle division by zero edge case
                double povertyPercentage = data.schoolAgeChildren == 0 ? 0.0 
                        : (double) data.povertyChildren / data.schoolAgeChildren * 100;

                System.out.printf("%-10s %-15d %-20d %-25d %-20.2f%%\n", 
                        stateCode, data.totalPopulation, data.schoolAgeChildren, data.povertyChildren, povertyPercentage);
            }

        } catch (IOException e) {
            System.err.println("Error reading file: " + e.getMessage());
        } catch (NumberFormatException e) {
            System.err.println("Error parsing numeric data: " + e.getMessage());
        }
    }
}

Key Fixes & Improvements: #

1. Variable Whitespace Handling

   • Instead of split(" "), we use Scanner which automatically splits on any whitespace (spaces, tabs, etc.)—this eliminates empty array elements from multiple spaces entirely.
   • If you prefer using split, replace the Scanner logic with:

     String[] parts = line.trim().split("\\s+"); // \\s+ matches one or more whitespace characters
     String stateCode = parts[0];
     int totalPop = Integer.parseInt(parts[1]);
     int schoolAge = Integer.parseInt(parts[2]);
     int poverty = Integer.parseInt(parts[3]);
     

   • trim() removes leading/trailing whitespace to avoid unexpected empty elements at the start of the array.

2. State-Wise Grouped Aggregation

   • A HashMap<String, StateAggregate> stores summed values per state code. The StateAggregate class keeps track of the three totals in an organized, reusable way.
   • getOrDefault() simplifies checking for existing state entries—if no entry exists, we create a new StateAggregate instance.

3. Percentage Calculation

   • We cast values to double before division to avoid integer division (which would truncate results to 0 if poverty counts are smaller than school age counts).
   • Added a check for division by zero (in case a state has no school age children) to prevent runtime errors.

4. Robust Resource Management

   • Try-with-resources (try (BufferedReader reader = ...)) ensures the file reader is automatically closed, even if an exception occurs.

5. Clean Formatted Output

   • printf aligns columns neatly, making the final results easy to read and interpret.

Why Your Original Test.java Failed: #

• It summed all rows into a single totalPop variable instead of grouping by state code.
• split(" ") creates empty strings in the array when multiple spaces are present, so population[1] wouldn't always point to the total population value (leading to parsing errors).

内容的提问来源于stack exchange，提问作者Billiejean711