[英]Java - Scanner.nextLine() skipping even when accounting for new line
[英]scanner skipping new line
我試圖理解java中的掃描器類,為什么這個代碼只打印第一部分中的第一行而不是第2部分中的所有信息。
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();
}
}
我嘗試使用分隔符,但沒有成功。
如果您運行調試器並逐步執行getNextEntry
方法,您將看到在第二次調用時, Scanner
會拋出NoSuchElementException
。 發生這種情況的原因是因為第一個Scanner
消耗了部分ByteArrayInputStream
。
一個修復你可以做的是創建Scanner
您的面前while
循環,並通過在Scanner
以getNextEntry
強似在ByteArrayInputStream
。
public static String getNextEntry(Scanner sin) {
...
Scanner sin = new Scanner(in);
String entry;
while ((entry = getNextEntry(sin)) != null) {
就第2部分而言, PrintWriter
沒有被刷新。 如果添加pout.flush()
至底部putNextEntry
應該會導致數據被發送到您的文件。 對於PrintWriter
對象,只有在調用println
, printf
, format
或flush
時才刷新數據。
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 + " ");
pout.flush();
}
不過,我建議創建並傳入類似於掃描儀的PrintWriter。 減少創建的資源,並在多次調用putNextEntry
后清除所有結束。
問題是您在getNextEntry
中創建了Scanner
對象,當該對象被銷毀時,它會關閉流。 嘗試將Scanner作為參數傳遞而不是像流一樣(對於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();
}
}
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