我不明白為什么我的程序沒有循環

Question

我試圖讓這個文件循環，但我在最后一個 if 語句（用箭頭標記）上一直出錯。

該程序應該讀入一個文件，第一行是客戶的姓名。
在第二行，第一個數字是要移除的樹木數量（每棵樹 150 個），第二個數字是要修剪的樹木（每小時 50 個）。
第三行是所有要移除的樹樁及其直徑（一個數字是一個樹樁，也是它的直徑）。

這是應該被讀取的文件 ( http://pastebin.com/gXkujcaM )。

public class Prog_5 {

    public static void main(String[] args) throws FileNotFoundException {
        String name = "Joe";
        double trees = 0;
        double treeTrimming = 0;
        double stumpInches = 0;
        double stumpTotal = 0;
        double total = 0;
        double totalRev = 0;

        Scanner in = new Scanner(System.in);
        System.out.print("Input file: ");
        String inputFile = in.nextLine();

        System.out.print("Output file: ");
        String outputFile = in.nextLine();
        in.close();

        File input = new File(inputFile);
        in = new Scanner(input);
        PrintWriter output = new PrintWriter(outputFile);

        while(in.hasNext()){

        name = in.nextLine();
        output.println("Customer: " + name);
        System.out.println("Customer: " + name);

        trees = in.nextDouble();
        trees *= 150;
        output.println("Tree Removal: $" + trees);
        System.out.println("Tree Removal: $" + trees);

        treeTrimming = in.nextDouble();
        treeTrimming *= 50;
        output.println("Tree Trimming: $" + treeTrimming);
        System.out.println("Tree Trimming: $" + treeTrimming);

        while (in.hasNextDouble()) {
            stumpInches = in.nextDouble();
            if (stumpInches != -1) {
                stumpTotal = stumpTotal + 30;
                if (stumpInches > 12) {
                    stumpInches -= 12;
                    stumpInches *= 2;
                }
                stumpTotal += stumpInches;
            }

        }
        output.println("Stump Removal: $" + stumpTotal);
        System.out.println("Stump Removal: $" + stumpTotal);

        total = (trees + treeTrimming + stumpTotal);
        output.println("Total: $" + total);
        System.out.println("Total: $" + total);

        totalRev += total;
        stumpTotal = 0;
        trees = 0;
        treeTrimming = 0;

        if(in.hasNext());
            in.next();
        }

        output.close();

    }

}

Answer 1

這是你的 if 循環問題。 你應該像下面這樣寫。 但是你用 ; 終止了它

if(in.hasNext()){
       in.next();
        }

所以每次到達EOF都會拋出nosuchelement異常

Answer 2

如果條件在最后，則不需要外部 while 循環。 內部 while 循環負責您的程序打算做什么。 PFB 修正代碼：

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

public class Prog_5 {

    public static void main(String[] args) throws FileNotFoundException {
        String name = "Joe";
        double trees = 0;
        double treeTrimming = 0;
        double stumpInches = 0;
        double stumpTotal = 0;
        double total = 0;
        double totalRev = 0;

        Scanner in = new Scanner(System.in);
        System.out.print("Input file: ");
        String inputFile = in.nextLine();

        System.out.print("Output file: ");
        String outputFile = in.nextLine();
        in.close();

        File input = new File(inputFile);
        in = new Scanner(input);
        PrintWriter output = new PrintWriter(outputFile);

        // while (in.hasNext()) {

        name = in.nextLine();
        output.println("Customer: " + name);
        System.out.println("Customer: " + name);

        trees = in.nextDouble();
        trees *= 150;
        output.println("Tree Removal: $" + trees);
        System.out.println("Tree Removal: $" + trees);

        treeTrimming = in.nextDouble();
        treeTrimming *= 50;
        output.println("Tree Trimming: $" + treeTrimming);
        System.out.println("Tree Trimming: $" + treeTrimming);

        while (in.hasNextDouble()) {
            stumpInches = in.nextDouble();
            if (stumpInches != -1) {
                stumpTotal = stumpTotal + 30;
                if (stumpInches > 12) {
                    stumpInches -= 12;
                    stumpInches *= 2;
                }
                stumpTotal += stumpInches;
            }

        }
        output.println("Stump Removal: $" + stumpTotal);
        System.out.println("Stump Removal: $" + stumpTotal);

        total = (trees + treeTrimming + stumpTotal);
        output.println("Total: $" + total);
        System.out.println("Total: $" + total);

        totalRev += total;
        stumpTotal = 0;
        trees = 0;
        treeTrimming = 0;

        // if (in.hasNext())
        // ;
        // in.next();
        // }
        in.close();
        output.close();

    }
}