未报告的exceptionFileNotFoundException; 必须被抓住或宣布被抛出
我的代码导致以下错误 – 这是为什么？
2 errors found: File: C:\Users\Name\P4.java [line: 44] Error: C:\Users\Name\P4.java:44: unreported exception FileNotFoundException; must be caught or declared to be thrown File: C:\Users\Name\P4.java [line: 46] Error: C:\Users\Name\P4.java:46: exception java.io.FileNotFoundException is never thrown in body of corresponding try statement 这是导致错误的代码：
case Command.CMD_DO: NextCommand tmpReader; try { tmpReader = new NextCommand( c.getArg() ); } catch (FileNotFoundException e) { tmpReader = null; System.out.println( "Unable to open file:"); System.out.println( " " + e.getMessage()); }
全class都在这里：
import java.io.FileNotFoundException; import java.util.Stack; public class P4 { public static void main( String[] args ) { // Start off assuming we're reading from the console and create a stack // for storing "pushed" readers NextCommand reader = new NextCommand(); Stack cmdStack = new Stack(); // The command we get and a flag to indicate whether it's time to exit Command c; boolean userRequestsExit = false; // For storing the history. We keep track of the depth of the stack, too. // Note that we could just use cmdStack.size() but that's a Vector operation rather // than a "pure" stack operation, so for the sake of pedagogy, we won't... History h = new History(); int nestingLevel = 0; do { // Get a command c = reader.get(); h.add( c, nestingLevel ); switch (c.getCommand()) { // Do nothing in response to a comment case Command.CMD_COMMENT: break; // DO filename. See if we can start a reader up from the file. // If not, then print an error and continue from where we left off. // If so, push the current reader onto a stack and continue with the new one case Command.CMD_DO: NextCommand tmpReader; try { tmpReader = new NextCommand( c.getArg() ); } catch (FileNotFoundException e) { tmpReader = null; System.out.println( "Unable to open file:"); System.out.println( " " + e.getMessage()); } // Success. Save current reader and switch to new one. We are // now nested one level deeper in DO files... if (tmpReader!=null) { cmdStack.push(reader); reader = tmpReader; nestingLevel++; } break; // DOC id "title" text case Command.CMD_DOC: String[] docParts = c.getArg().split( "\"" ); if (docParts.length != 3) { System.out.println( "ERROR: Invalid format: use DOC docid \"title\" text"); } else { Document d = new Document( docParts[0].trim(), docParts[1].trim(), docParts[2].trim() ); //Add document to database Database.documentList.add(d); if (d==null || d.getDocid()==null) System.out.println( "ERROR: Invalid DOC: " + d.getTitle() ); else System.out.println( "Added document " + d.getDocid() ); } break; // HISTORY case Command.CMD_HISTORY: System.out.println( h ); break; // END. If the command-source stack is empty, we're done. // Otherwise, revert to the previous one and note that we are now // one level back up in the nesting of DO files. case Command.CMD_END: if (cmdStack.empty()) userRequestsExit = true; else { reader = cmdStack.pop(); nestingLevel--; } break; // Others default: System.out.println ("Only DOC, DO, HISTORY, and END commands work right now."); } } while (!userRequestsExit); // Courtesy exit message. System.out.println( "Thank you for playing." ); System.out.println( "You processed " + h.numCommands() + " command" + (h.numCommands()==1 ? "" : "s") + " before you exited." ); } }
这是NextCommand类：
import java.util.*; import java.io.*; public class NextCommand implements NextCommandInterface { private Scanner inStream; private boolean promptUser; private String nameOfFile; // Default constructor uses system input and requests prompting public NextCommand() { inStream = new Scanner( System.in ); promptUser = true; nameOfFile = null; } // Alternate constructor to allow input from a file (no prompting) public NextCommand(String filename) throws FileNotFoundException { inStream = new Scanner( new File(filename)); promptUser = false; nameOfFile = filename; } // Ask user for a command and process it to return a Command public Command get() { String inLine; // If we have no way to get input, pretend we hit the end if (inStream==null) return new Command( "END" ); // Optionally prompt for the command if (promptUser) System.out.print( "Command? "); // Get a command (have to make sure EOF wasn't pressed) if (!inStream.hasNextLine()) return new Command( "END" ); inLine = inStream.nextLine(); // Clean it up and return the results return new Command( inLine ); } // A whimsical way to print this object out. public String toString() { if (nameOfFile == null) return "Commands being accepted from standard input"; else return "Commands being accepted from " + nameOfFile; } }
编译错误说P4中有两个版本的FileNotFoundException 。 您已导入并尝试捕获java.io.FileNotFoundException 。 然后还有一些其他的FileNotFoundExceptionexception（根据编译器）由NextCommand构造函数抛出。
但这没有意义……
如果代码是你向我们展示的，并且编译错误就像你向我们展示的那样，那么我能想到的唯一解释就是你需要重新编译一些东西 。
具体来说，您已在NextCommand更改了导入，而无需重新编译它，然后再重新编译P4类。
我建议您删除然后重新编译所有“.class”文件。
唯一的另一种可能性是你在与我们展示的两个类相同的包中定义了一个虚假版本的FileNotFoundException 。 如果你这样做，你的虚假课程将优先于真实课程。 但是为了使这个“工作”作为解释，你还需要对Scanner做同样的事情……因为真正的Scanner构造函数会抛出真正的FileNotFoundException …这个被检查，因此必须在NextCommand构造函数签名。 在这一点上，我将把它视为“难以置信”。
向您的main()方法调用添加抛出FileNotFoundException ，喜欢这样：
public static void main(String[] args) throws FileNotFoundException {
然后删除try-catch块。 让我知道这是怎么回事。