我一直在踢这段代码一段时间，我想我知道一般问题是什么，我无法弄清楚如何纠正它。我收到以下错误：
C:\Documents and Settings\Joe King\My Documents\418.85A Java\Project5>javac Project5.java
Project5.java:408: error: variable boatNames might not have been initialized
boatArray1 = new Boat[boatNames.length];
^
1 error
问题是我的boatNames数组在try / catch块中，我认为这是将它与其余代码隔离开来。如何从try / catch块中取出boatNames数组？
我的代码如下：
class Project5{
public static void main(String[] args){
String[] boatNames;
Boat[] boatArray1;
Boat[] boatArray2;
String result = " ";
String name = null;
char firstChar;
char firstLetter;
char secondLetter;
int totalRead;
int i;
int j;
int k;
int l;
int m;
Path inPath = Paths.get("C:/Documents and Settings/Joe King/My Documents/418.85A Java/Projects/Input").resolve("Boat Names.txt");
if(!Files.exists(inPath)){
System.out.println(inPath + " does not exist. Terminating the program.");
System.exit(1);
}
try(BufferedReader fileIn = Files.newBufferedReader(inPath, Charset.forName("UTF-16"))){
totalRead = 0;
while(fileIn.readLine() != null){
name = fileIn.readLine();
++totalRead;
name = null;
}
boatNames = new String[totalRead];
for(i = 0 ; i < boatNames.length ; ++i){
name = fileIn.readLine();
boatNames[i] = name;
name = null;
}
}catch(IOException e){
System.err.println("Error writing file: " + inPath);
e.printStackTrace();
}
Path outPath = Paths.get("C:/Documents and Settings/Joe King/My Documents/418.85A Java/Projects/Output").resolve("Fleet Registry.txt");
try{
Files.createDirectories(outPath.getParent());
}catch(IOException e){
System.err.println("Error creating directory: " + outPath.getParent());
e.printStackTrace();
System.exit(1);
}
boatArray1 = new Boat[boatNames.length];
if(boatNames.length > 0){
try(BufferedWriter fileOut = Files.newBufferedWriter(outPath, Charset.forName("UTF-16"))){
for(j = 0 ; j < boatNames.length ; j++){
String delimiters = "[. ,]";
int limit = -1;
String[]tokens = boatNames[j].split(delimiters, limit);
for(k = 0 ; k < tokens.length ; ++k){
firstChar = tokens[k].charAt(0);
firstChar = Character.toUpperCase(firstChar);
char[] tokenArray = tokens[k].toCharArray();
String text = new String(tokenArray, 1, (tokenArray.length - 1) );
tokens[k] = firstChar + text;
result = result + tokens[k] + " ";
if(k != tokens.length - 1){
continue;
}else{
result = result.trim();
boatNames[k] = result;
result = " ";
}
}
firstLetter = boatNames[j].charAt(0);
if((firstLetter == 'B') || (firstLetter == 'C') || (firstLetter == 'N')){
boatArray1[j] = new RaceBoat();
}else{
boatArray1[j] = new SailBoat();
}
boatArray1[j].christenBoat(boatNames[j]);
}
System.out.println("\n");
for(l = 0 ; l < boatNames.length ; ++l){
secondLetter = Character.toUpperCase(boatNames[l].charAt(1));
if((secondLetter == 'A') || (secondLetter == 'E')){
if(l > 0){
fileOut.newLine();
}
fileOut.write(boatArray1[l].goFast());
}else{
if(l > 0){
fileOut.newLine();
}
fileOut.write(boatArray1[l].goSlow());
}
fileOut.newLine();
fileOut.write(boatArray1[l].launchBoat());
fileOut.newLine();
fileOut.write(boatArray1[l].whatIsBoatState());
fileOut.newLine();
}
boatArray2 = new Boat[3];
boatArray2[0] = new SailBoat();
boatArray2[1] = new RaceBoat("Endurance", true);
boatArray2[2] = new RaceBoat(false);
for(m = 0 ; m < boatArray2.length ; ++m){
fileOut.newLine();
fileOut.write(boatArray2[m].toString());
fileOut.newLine();
fileOut.write(boatArray2[m].launchBoat());
fileOut.newLine();
fileOut.write(boatArray2[m].whatIsBoatState());
fileOut.newLine();
}
fileOut.newLine();
fileOut.write("There are " + Boat.boatCount + " boats in the fleet this morning.");
}catch(IOException e){
System.err.println("Error writing outPath: " + outPath);
e.printStackTrace();
}
}else{
System.out.println("\n\n\nArgh!... you forgot to enter ship names scalawag!" +
"\n\n\n\tPlease try again!");
}
System.out.println("\nThe Fleet Registry is completed, press ENTER to continue.\n");
try{
System.in.read();
} catch(IOException e){
return;
}
}
}
谢谢大家，我输入了以下内容：
if(boatNames != null){
boatArray1 = new Boat[boatNames.length];
if(boatNames.length > 0){
try(BufferedWriter fileOut = Files.newBufferedWriter(outPath, Charset.forName("UTF-16"))){
for(j = 0 ; j < boatNames.length ; j++){
String delimiters = "[. ,]";
int limit = -1;
String[]tokens = boatNames[j].split(delimiters, limit);
for(k = 0 ; k < tokens.length ; ++k){
firstChar = tokens[k].charAt(0);
firstChar = Character.toUpperCase(firstChar);
char[] tokenArray = tokens[k].toCharArray();
String text = new String(tokenArray, 1, (tokenArray.length - 1) );
tokens[k] = firstChar + text;
result = result + tokens[k] + " ";
if(k != tokens.length - 1){
continue;
}else{
result = result.trim();
boatNames[k] = result;
result = " ";
}
}
firstLetter = boatNames[j].charAt(0);
if((firstLetter == 'B') || (firstLetter == 'C') || (firstLetter == 'N')){
boatArray1[j] = new RaceBoat();
}else{
boatArray1[j] = new SailBoat();
}
boatArray1[j].christenBoat(boatNames[j]);
}
System.out.println("\n");
for(l = 0 ; l < boatNames.length ; ++l){
secondLetter = Character.toUpperCase(boatNames[l].charAt(1));
if((secondLetter == 'A') || (secondLetter == 'E')){
if(l > 0){
fileOut.newLine();
}
fileOut.write(boatArray1[l].goFast());
}else{
if(l > 0){
fileOut.newLine();
}
fileOut.write(boatArray1[l].goSlow());
}
fileOut.newLine();
fileOut.write(boatArray1[l].launchBoat());
fileOut.newLine();
fileOut.write(boatArray1[l].whatIsBoatState());
fileOut.newLine();
}
boatArray2 = new Boat[3];
boatArray2[0] = new SailBoat();
boatArray2[1] = new RaceBoat("Endurance", true);
boatArray2[2] = new RaceBoat(false);
for(m = 0 ; m < boatArray2.length ; ++m){
fileOut.newLine();
fileOut.write(boatArray2[m].toString());
fileOut.newLine();
fileOut.write(boatArray2[m].launchBoat());
fileOut.newLine();
fileOut.write(boatArray2[m].whatIsBoatState());
fileOut.newLine();
}
fileOut.newLine();
fileOut.write("There are " + Boat.boatCount + " boats in the fleet this morning.");
}catch(IOException e){
System.err.println("Error writing outPath: " + outPath);
e.printStackTrace();
}
}else{
System.out.println("\n\n\nArgh!... you forgot to enter ship names scalawag!" +
"\n\n\n\tPlease try again!");
}
System.out.println("\nThe Fleet Registry is completed, press ENTER to continue.\n");
try{
System.in.read();
} catch(IOException e){
return;
}
}
现在我收到以下错误：
C:\Documents and Settings\Joe King\My Documents\418.85A Java\Project5>java Project5
Exception in thread "main" java.lang.NullPointerException
at Project5.main(Project5.java:424)
这对我来说没有意义，为了到达第424行，boatNames数组不能为null，因为在第424行之前多次使用了boatNames的长度。我错过了什么？
由于
答案 0 :(得分：9)
变量 在try/catch之外，否则编译错误会有所不同。问题是初始化位于try块内，因此try之后的代码无法确定变量是否已初始化。
有两种方法可以解决这个问题：
声明变量时初始化变量。只需使用它就足够了：
String[] boatNames = null;
移动try块内使用该变量的所有代码。这通常是一个很好的策略，但前提是你的方法很小。在你的情况下，我不建议这样做，因为你的方法太长了。现在，如果您可以将代码分解为更短的方法，那么将变量的范围限制为单个try块将是有道理的。
答案 1 :(得分：4)
在try / catch块之前，像这样初始化数组：
String[] boatNames = null;
答案 2 :(得分：4)
您已在try block
之外声明了数组String[] boatNames;
它将在第一个试块
下初始化boatNames = new String[totalRead];
问题在这里boatArray1 = new Boat[boatNames.length];
原因是，您的编译器无法知道boatNames初始化是否成功，因为可能存在异常并且初始化将失败。
作为声明的一部分，您可以这样做：
String[] boatNames = null; // This will fix your immediate problem
但这样做可能会导致NullPointerException，因为您的文件读取可能会失败。
要解决此问题，请在使用之前对阵列进行空检查。
if(boatNames == null){
// I am not going to go further or will take corrective measures here
}
答案 3 :(得分：0)
这里的编译器考虑了在boatNames初始化之前可能在try块中引发异常的可能性，因此它给出了编译器错误might not have been initialized。 可能在这里很重要！
这里的理想解决方案是调整代码结构并放入
boatArray1 = new Boat[boatNames.length];
在同一个试块中！