java - 扫描仪跳过新行

Question

我想了解 java 中的扫描器类，有人知道为什么这段代码只打印第一部分的第一行而不是第二部分的所有信息吗。

import java.io.ByteArrayInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.NoSuchElementException;
import java.util.Scanner;

public class BadParse {

public static String getNextEntry(InputStream in) {
    Scanner sin = new Scanner(in);

    try {
        String ssn = sin.next();
        String name = sin.next();
        int age = sin.nextInt();

        return name + "(" + ssn + ") is " + age + " years old.";
    } catch (NoSuchElementException e) {
        return null;
    }
}

public static void putNextEntry(String ssn, String name, int age, OutputStream out) {
    PrintWriter pout = new PrintWriter(new OutputStreamWriter(out));

    pout.print(ssn + " ");
    pout.print(name + " ");
    pout.print(age + " ");
}

public static void main(String[] args) throws IOException {

    // Part I
    String input = "1234567890 John 20\n0987654321 Beth 18\n2468101214 Jack 19\n";
    InputStream in = new ByteArrayInputStream(input.getBytes());

    String entry;
    while ((entry = getNextEntry(in)) != null) {
        System.out.println(entry);
    }

    // Part II
    OutputStream out = new FileOutputStream("data");

    putNextEntry("1234567890", "John", 20, out);
    putNextEntry("0987654321", "Beth", 18, out);
    putNextEntry("2468101214", "Jack", 19, out);

    out.close();
}

我尝试使用定界符但没有成功。

Answer 1

问题是您正在 getNextEntry 中创建 Scanner 对象，当该对象被销毁时，它会关闭流。尝试将 Scanner 作为参数而不是像流一样传递(对于 PrintWriter 也是如此):

 import java.io.ByteArrayInputStream;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.NoSuchElementException;
import java.util.Scanner;

public class BadParse {
public static String getNextEntry(Scanner sin) {

    try {
        String ssn = sin.next();
        String name = sin.next();
        int age = sin.nextInt();

        return name + "(" + ssn + ") is " + age + " years old.";
    } catch (NoSuchElementException e) {
        return null;
    }
}

public static void putNextEntry(String ssn, String name, int age, PrintWriter pout) {

    pout.print(ssn + " ");
    pout.print(name + " ");
    pout.print(age + " ");
}

public static void main(String[] args) throws IOException {

    // Part I
    String input = "1234567890 John 20\n0987654321 Beth 18\n2468101214 Jack 19\n";
    InputStream in = new ByteArrayInputStream(input.getBytes());
    Scanner sin = new Scanner(in);

    String entry;
    while ((entry = getNextEntry(sin)) != null) {
        System.out.println(entry);
    }

    // Part II
    OutputStream out = new FileOutputStream("data");
    PrintWriter pout = new PrintWriter(new OutputStreamWriter(out));

    putNextEntry("1234567890", "John", 20, pout);
    putNextEntry("0987654321", "Beth", 18, pout);
    putNextEntry("2468101214", "Jack", 19, pout);

    pout.close();
}
}