nextLine()方法不接受输入。但是next()有。为什么会这样呢？

Question

我正在使用Fretts。下面是代码片段。

public static void main(String[] args){
Scanner src=new Scanner(System.in);
String st,classname,filename;
int input=0;
char O_curlybrace,O_roundbrace,C_curlybrace,C_roundbrace;
File f=null;
boolean boo=false;
try
{
System.setProperty("freetts.voices",
com.sun.speech.freetts.en.us.cmu_us_kal.KevinVoiceDirectory");
Central.registerEngineCentral
        ("com.sun.speech.freetts.jsapi.FreeTTSEngineCentral");
        Synthesizer synthesizer =
        Central.createSynthesizer(new SynthesizerModeDesc(Locale.US));
        synthesizer.allocate();
        synthesizer.resume();
        System.out.println("Welcome to world of programming");
        synthesizer.speakPlainText("Welcome to world of programming", null);            
        synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
        synthesizer.speakPlainText("Start your java programming now.", null);
        System.out.println("Start your java programming now");
        synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
        synthesizer.speakPlainText("Enter your file name", null);
        System.out.println("Enter your file name");
        st=src.next();
        st=
        filename=st.substring(0,1).toUpperCase();
        classname=filename.concat(st.substring(1));
        synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
        synthesizer.speakPlainText("Creating new java file", null);
        System.out.println("Creating new java file");
        synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
        FileWriter fstream = new FileWriter(classname+".txt",true);
        BufferedWriter output = new BufferedWriter(fstream);
        output.write("import java.io.*;");
        output.newLine();
        output.append("import java.util.*");
        output.newLine();
        synthesizer.speakPlainText("File created", null);
        System.out.println("File created: ");
        synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
        synthesizer.speakPlainText("Importing basic packages.", null);
        System.out.println("Importing basic packages.");
        synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
        Thread.sleep(1500);
        synthesizer.speakPlainText("Packages imported.", null);
        System.out.println("Packages imported");
        Thread.sleep(500);
        synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
        synthesizer.speakPlainText("Enter 1 to create public class", null);
        System.out.println("Enter 1 to create public class");
        synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
        input=src.nextInt();
        if(input==1)
        {
            synthesizer.speakPlainText("Creating public class", null);
            System.out.println("Creating public class");
            synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
            Thread.sleep(2000);
            synthesizer.speakPlainText("Done", null);
            System.out.println("Done.");
            synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
            output.write("public class "+classname);
            output.newLine();
            output.append("{");
            output.newLine();

        }            
        synthesizer.speakPlainText("Press 2 to create main function", null);
        System.out.println("Press 2 to create main function");
        input=src.nextInt();
        if(input==2)
        {
            synthesizer.speakPlainText("Creating main function", null);
            System.out.println("Creating function");
            synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
            Thread.sleep(2000);
            synthesizer.speakPlainText("Done", null);
            System.out.println("Done.");
            synthesizer.waitEngineState(Synthesizer.QUEUE_EMPTY);
            output.write("public static void main(String args[]) ");
            output.newLine();
            output.append("{");
            output.newLine();
        }
        synthesizer.speakPlainText("Press 3 to print something", null);
        System.out.println("Press 3 to print something");
        input=src.nextInt();
        if(input==3)
        {
            synthesizer.speakPlainText("Type something that you want to print", null);
            System.out.println("Type something that you want to print:");
            String print=src.nextLine();
            output.write("System.out.println(\""+print+"\");");
            output.close();
        }
        synthesizer.deallocate();
     }
    catch(Exception e)
    {
    }

第2行和第3行执行得很好，但第3行开始的程序被终止。如果我使用的是next()而不是nextLine()，那么它将完美地工作。如何解决这个问题？

Answer 1

我认为看到更多的代码是有帮助的。我注意到在代码片段中没有声明src。src以前用过吗？

如果以前使用过，那么src的缓冲区可能不是空的。例如，.nextInt()将把enter字符留在缓冲区中，因为它不是整数。如果enter字符仍在缓冲区中，.nextLine()将将其读取为空行。您可以尝试在src.nextLine()之前调用.println()并丢弃输入。这将清除缓冲区。

编辑:好的，这就是问题所在：

input=src.nextInt();

你输入了两样东西，数字和eol字符。.nextInt()将eol字符留在缓冲区中，所以下次调用.nextLine()时，它会读取缓冲区，查看eol字符，并假设您只是输入了空行。因此，print = "“此处：

String print=src.nextLine();

我会用两个扫描器，一个用于ints，另一个用于字符串。或者在调用.nextLine()之前清除缓冲区。