java Scanner 类 hasNextLine 无限循环
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原文地址: http://stackoverflow.com/questions/7974238/
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Scanner Class hasNextLine infinite loop
提问by KWJ2104
why does this piece of code go into an infinite loop when I try to give it a basic text file?
当我尝试给它一个基本的文本文件时，为什么这段代码会进入无限循环？
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.*;
public class TestFile
{
public static void main(String args[]) throws IOException
{
// Read in input file
File input = new File(args[0]);
Scanner freader = new Scanner(input);
while (freader.hasNextLine()) {
System.out.println("hi");
}
freader.close();
}
}
The print line just keeps going.
打印线一直在运行。
回答by b.buchhold
Because hasNexLine()does neither get the line nor change the state of the scanner. if it's true once, and no other methods of the scanner are called, it'll always be true.
因为hasNexLine()既不会得到线路也不会改变扫描仪的状态。如果它一次为真，并且没有调用扫描仪的其他方法，则它将始终为真。
回答by OscarRyz
Because you have to consume the nextLine so the code should be:
因为你必须使用 nextLine 所以代码应该是：
while ( theScanner.hasNextLine() ) {
String theLine = theScanner.nextLine();
}
If you don't invoke nextLine()you will always be watching at the same line and it will always answer true to that.
如果您不调用，nextLine()您将始终在同一行观看，并且它始终会对此做出正确的回答。
回答by AusCBloke
Add a call to nextLineor any other Scannermethod that'll read in some input inside the whileloop.
添加对循环内某些输入的调用nextLine或任何其他Scanner方法while。
At the moment you're just repeatedly calling hasNextLine(which onlyreturns a boolean, it doesn't modify the stream) without retrieving any input from freader, so if freaderinitially has another line within its input hasNextLinewill alwaysreturn true and your loop is essentially while (true).
此刻你只是重复调用hasNextLine（其中只返回一个boolean未经任何检索输入，它不会改变流）freader，因此，如果freader最初有其内输入另一行hasNextLine会始终返回true，你的循环本质while (true)。
