扫描仪不能自动关闭

Question

package org.test;

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class RegTest {
    public static void main(String[] args) throws InterruptedException {
        String str = readLine("Enter String :");
        String patternString = readLine("Enter pattern to search :");

        Pattern pattern = Pattern.compile(patternString);
        Matcher matcher = pattern.matcher(str);

        System.out.print("match positions: "); // matches positions
        while(matcher.find()) {
            System.out.print(matcher.start() + " ");
        }
        System.out.println("");
    }


    static String readLine(String message){
        String strLine;
            try (Scanner in = new Scanner(System.in)) {
                System.out.println(message);
                strLine= in.nextLine();
            }
        return strLine;
    }
}

输出为：

输入字符串:
WEWEW
输入模式搜索:
线程“main”java.util.NoSuchelementException：在java.util.scanner.nextline（scanner.java:1585)
在org.test.regtest.readline（regtest.java:39)
在org.test.regtest.main（regtest.java:22)

Answer 1

当使用资源尝试（autoclosable）关闭扫描器时，它也会关闭inputstream，使其在将来不可用。

由于System.in是全局inputstream，这意味着第二个扫描程序不能从inputstream中读取任何内容，因为它已经关闭，并且它会抛出异常。

我会更改代码以重用sanner进行两次读取。

public static void main(String[] args) throws InterruptedException {
    try (Scanner in = new Scanner(System.in)) {
        String str = readLine(in, "Enter String :");
        String patternString = readLine(in, "Enter pattern to search :");

        Pattern pattern = Pattern.compile(patternString);
        Matcher matcher = pattern.matcher(str);

        System.out.print("match positions: "); // matches positions
        while (matcher.find()) {
            System.out.print(matcher.start() + " ");
        }
        System.out.println("");
    }

}

static String readLine(Scanner in, String message) {
    String strLine;
    System.out.println(message);
    strLine = in.nextLine();
    return strLine;
}