我想要做一个函数，它可以获取一个字符串，并在其中发现内联注释时将其删除。我知道这听起来很简单，但我想确保我做得对，例如：
private String filterString(String code) {
// lets say code = "some code //comment inside"
// return the string "some code" (without the comment)
}
我想到了两种方法：请随意提出其他建议
您能告诉我哪种方法最好，并向我展示如何完成吗？（请不要提供过于高级的解决方案）
编辑：是否可以通过Scanner对象以某种方式完成此操作？（无论如何，我都在使用此对象）
如果您想要一个更高效的正则表达式来匹配所有类型的注释，请使用以下内容：
replaceAll("(?:/\\*(?:[^*]|(?:\\*+[^*/]))*\\*+/)|(?://.*)","");
来源： http://ostermiller.org/findcomment.html
编辑：
如果您不确定是否使用正则表达式，另一种解决方案是设计一个如下的小自动机:
public static String removeComments(String code){
final int outsideComment=0;
final int insideLineComment=1;
final int insideblockComment=2;
final int insideblockComment_noNewLineYet=3; // we want to have at least one new line in the result if the block is not inline.
int currentState=outsideComment;
String endResult="";
Scanner s= new Scanner(code);
s.useDelimiter("");
while(s.hasNext()){
String c=s.next();
switch(currentState){
case outsideComment:
if(c.equals("/") && s.hasNext()){
String c2=s.next();
if(c2.equals("/"))
currentState=insideLineComment;
else if(c2.equals("*")){
currentState=insideblockComment_noNewLineYet;
}
else
endResult+=c+c2;
}
else
endResult+=c;
break;
case insideLineComment:
if(c.equals("\n")){
currentState=outsideComment;
endResult+="\n";
}
break;
case insideblockComment_noNewLineYet:
if(c.equals("\n")){
endResult+="\n";
currentState=insideblockComment;
}
case insideblockComment:
while(c.equals("*") && s.hasNext()){
String c2=s.next();
if(c2.equals("/")){
currentState=outsideComment;
break;
}
}
}
}
s.close();
return endResult;
}
最好的方法是使用正则表达式。
首先找到/**/注释，然后删除所有//注释。例如：
private String filterString(String code) {
String partialFiltered = code.replaceAll("/\\*.*\\*/", "");
String fullFiltered = partialFiltered.replaceAll("//.*(?=\\n)", "")
}
只需使用String类中的replaceAll方法，结合简单的正则表达式即可。下面是具体操作：
import java.util.*;
import java.lang.*;
class Main
{
public static void main (String[] args) throws java.lang.Exception
{
String s = "private String filterString(String code) {\n" +
" // lets say code = \"some code //comment inside\"\n" +
" // return the string \"some code\" (without the comment)\n}";
s = s.replaceAll("//.*?\n","\n");
System.out.println("s=" + s);
}
}
s = s.replaceAll("//.*?\n","\n");
@Christian Hujer一直正确指出，如果注释位于字符串内，则发布的许多或所有解决方案都会失败。
@Loïc Gammaitoni建议他的自动机方法可以很容易地扩展到处理这种情况。以下是该扩展。
enum State { outsideComment, insideLineComment, insideblockComment, insideblockComment_noNewLineYet, insideString };
public static String removeComments(String code) {
State state = State.outsideComment;
StringBuilder result = new StringBuilder();
Scanner s = new Scanner(code);
s.useDelimiter("");
while (s.hasNext()) {
String c = s.next();
switch (state) {
case outsideComment:
if (c.equals("/") && s.hasNext()) {
String c2 = s.next();
if (c2.equals("/"))
state = State.insideLineComment;
else if (c2.equals("*")) {
state = State.insideblockComment_noNewLineYet;
} else {
result.append(c).append(c2);
}
} else {
result.append(c);
if (c.equals("\"")) {
state = State.insideString;
}
}
break;
case insideString:
result.append(c);
if (c.equals("\"")) {
state = State.outsideComment;
} else if (c.equals("\\") && s.hasNext()) {
result.append(s.next());
}
break;
case insideLineComment:
if (c.equals("\n")) {
state = State.outsideComment;
result.append("\n");
}
break;
case insideblockComment_noNewLineYet:
if (c.equals("\n")) {
result.append("\n");
state = State.insideblockComment;
}
case insideblockComment:
while (c.equals("*") && s.hasNext()) {
String c2 = s.next();
if (c2.equals("/")) {
state = State.outsideComment;
break;
}
}
}
}
s.close();
return result.toString();
}
使用正则表达式替换来查找常量子字符串之前的子字符串有点复杂。
你可以使用indexOf()来检查注释开始的位置，然后使用substring()获取第一部分，类似于：
String code = "some code // comment";
int offset = code.indexOf("//");
if (-1 != offset) {
code = code.substring(0, offset);
}
String url="http://www.google.com"; - jwl public static void main(String[] args) throws CommentRemoverException {
// root dir is: /Users/user/Projects/MyProject
// example for startInternalPath
CommentRemover commentRemover = new CommentRemover.CommentRemoverBuilder()
.removeJava(true) // Remove Java file Comments....
.removeJavaScript(true) // Remove JavaScript file Comments....
.removeJSP(true) // etc.. goes like that
.removeTodos(false) // Do Not Touch Todos (leave them alone)
.removeSingleLines(true) // Remove single line type comments
.removeMultiLines(true) // Remove multiple type comments
.startInternalPath("src.main.app") // Starts from {rootDir}/src/main/app , leave it empty string when you want to start from root dir
.setExcludePackages(new String[]{"src.main.java.app.pattern"}) // Refers to {rootDir}/src/main/java/app/pattern and skips this directory
.build();
CommentProcessor commentProcessor = new CommentProcessor(commentRemover);
commentProcessor.start();
}
public static void main(String[] args) throws CommentRemoverException {
// example for externalPath
CommentRemover commentRemover = new CommentRemover.CommentRemoverBuilder()
.removeJava(true) // Remove Java file Comments....
.removeJavaScript(true) // Remove JavaScript file Comments....
.removeJSP(true) // etc..
.removeTodos(true) // Remove todos
.removeSingleLines(false) // Do not remove single line type comments
.removeMultiLines(true) // Remove multiple type comments
.startExternalPath("/Users/user/Projects/MyOtherProject")// Give it full path for external directories
.setExcludePackages(new String[]{"src.main.java.model"}) // Refers to /Users/user/Projects/MyOtherProject/src/main/java/model and skips this directory.
.build();
CommentProcessor commentProcessor = new CommentProcessor(commentRemover);
commentProcessor.start();
}
简单的解决方案，不会删除额外的代码部分（如上面那些） // 对于任何读者都适用，您还可以迭代字符串列表
String str="";
String s;
while ((s = reader.readLine()) != null)
{
s=s.replaceAll("//.*","\n");
str+=s;
}
str=str.replaceAll("/\\*.*\\*/"," ");
对于扫描仪，请使用分隔符，
分隔符示例。
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
public class MainClass {
public static void main(String args[]) throws IOException {
FileWriter fout = new FileWriter("test.txt");
fout.write("2, 3.4, 5,6, 7.4, 9.1, 10.5, done");
fout.close();
FileReader fin = new FileReader("Test.txt");
Scanner src = new Scanner(fin);
// Set delimiters to space and comma.
// ", *" tells Scanner to match a comma and zero or more spaces as
// delimiters.
src.useDelimiter(", *");
// Read and sum numbers.
while (src.hasNext()) {
if (src.hasNextDouble()) {
System.out.println(src.nextDouble());
} else {
break;
}
}
fin.close();
}
}
使用分词器处理普通字符串
分词器：
// start with a String of space-separated words
String tags = "pizza pepperoni food cheese";
// convert each tag to a token
StringTokenizer st = new StringTokenizer(tags," ");
while ( st.hasMoreTokens() )
{
String token = (String)st.nextToken();
System.out.println(token);
}
http://www.devdaily.com/blog/post/java/java-faq-stringtokenizer-example
如果代码能够分别处理单行注释和多行注释，那将更好。有什么建议吗？
public class RemovingCommentsFromFile {
public static void main(String[] args) throws IOException {
BufferedReader fin = new BufferedReader(new FileReader("/home/pathtofilewithcomments/File"));
BufferedWriter fout = new BufferedWriter(new FileWriter("/home/result/File1"));
boolean multilinecomment = false;
boolean singlelinecomment = false;
int len,j;
String s = null;
while ((s = fin.readLine()) != null) {
StringBuilder obj = new StringBuilder(s);
len = obj.length();
for (int i = 0; i < len; i++) {
for (j = i; j < len; j++) {
if (obj.charAt(j) == '/' && obj.charAt(j + 1) == '*') {
j += 2;
multilinecomment = true;
continue;
} else if (obj.charAt(j) == '/' && obj.charAt(j + 1) == '/') {
singlelinecomment = true;
j = len;
break;
} else if (obj.charAt(j) == '*' && obj.charAt(j + 1) == '/') {
j += 2;
multilinecomment = false;
break;
} else if (multilinecomment == true)
continue;
else
break;
}
if (j == len)
{
singlelinecomment=false;
break;
}
else
i = j;
System.out.print((char)obj.charAt(i));
fout.write((char)obj.charAt(i));
}
System.out.println();
fout.write((char)10);
}
fin.close();
fout.close();
}