Question

import java.io.*;
import java.util.Random;

public class LargeDataset {
public static void main(String[] args) throws Exception {
    File file = new File("src/Salary.txt");
    if (file.exists()) {
        System.out.print("Sorry this file already exists.");
        System.exit(0);
    }
    String firstName = "";
    String lastName = "";
    String rank = "";
    double salaryRange = 0.0;

    for (int i = 1; i <= 1000; i++) {
        try (PrintWriter output = new PrintWriter(file))
        {
            firstName = "FirstName" + i;
            lastName = "LastName" + i;
            rank = generateRandomRank();
            if (rank == "assistant")
                salaryRange = generateSalary(50000.00, 80000.00);
            else if (rank == "associate")
                salaryRange = generateSalary(60000.00, 110000.00);
            else
                salaryRange = generateSalary(75000.00, 130000.00);
            output.printf("%s %s %s $%.2f", firstName, lastName, rank, salaryRange);
            output.println();
        }
    }
}

public static String generateRandomRank() {
    String[] rank = {"assistant", "associate", "full"};
    Random random1 = new Random();
    return rank[random1.nextInt(3)];
}

public static double generateSalary(double minSalary, double maxSalary) {
    double randomSalary = minSalary + Math.random() * (maxSalary - minSalary);
    return randomSalary;
 }  
}

大家好。我有一个生成1000行文本的程序，并将其保存到名为Salary的文件中。每行的格式为：firstNamei，lastNamei，随机排名和适合排名的随机薪水。但是当我运行这个程序时，它只输出循环的第1000行。但是我注意到，当我没有将PrintWriter放在try语句中并在循环后自行关闭它时，它运行正常并生成所有1000行。为什么它只根据现在的情况生成最后一行呢？

Answer 1

您应该打开PrintWriter 一次，然后从循环中多次写入，而不是相反：

try (PrintWriter output = new PrintWriter(file)) {
    for (int i = 1; i <= 1000; i++) {
        firstName = "FirstName" + i;
        lastName = "LastName" + i;
        rank = generateRandomRank();
        if (rank == "assistant")
            salaryRange = generateSalary(50000.00, 80000.00);
        else if (rank == "associate")
            salaryRange = generateSalary(60000.00, 110000.00);
        else
            salaryRange = generateSalary(75000.00, 130000.00);
        output.printf("%s %s %s $%.2f", firstName, lastName, rank, salaryRange);
        output.println();
    }
}

您应该使用上述模式而不是您拥有的模式。如果您想要对当前代码进行精确修复，那么您可以尝试在追加模式下打开PrintWriter：

for (int i=1; i <= 1000; i++) {
    try (PrintWriter output = new PrintWriter(new FileOutputStream(file, true)) {
        // same logic
    }
}

这也应该有效，因为现在，即使你为循环的每次迭代创建一个新的PrintWriter（效率低下），你也可以在追加模式下打开底层文件，所以每个新行应该写得正确。

Answer 2

每次迭代1000时，您都在创建新文件

for (int i = 1; i <= 1000; i++) {
    try (PrintWriter output = new PrintWriter(file))
    ...
}

在循环之前移动它

 try (PrintWriter output = new PrintWriter(file)) {
   for (int i = 1; i <= 1000; i++) {
   }
 }

仅输出最后一行循环

2 个答案: