Is there a way to get rid of buf?
public Option(String opt) {
String[] buf;
buf = opt.split("=");
key = buf[0];
value = buf[1];
}
I thought of something like { key, val } = opt.split("="); as it would be possible in Perl, IIRC.
There is java.util.Scanner, which gives back one token at a time. But it's a lot harder to use than split, and in my experience not worth the trouble for problems simple enough to handle w/ split.
Related
I have a String title and a List<String> bannedSubstrings. Now I want to perform a one line check if title is free of those bannedSubstrings.
My approach:
if(bannedSubstrings.stream().filter(bannedSubstring -> title.contains(bannedSubstring)).isEmpty()){
...
}
Unfortunately, there is no isEmpty() method for streams. So how would you solve the problem? Is there a one line solution?
Sounds like you want to read up on anyMatch:
if (bannedSubstrings.stream().anyMatch(title::contains)) {
// bad words!
}
Inversely, there's also noneMatch:
if (bannedSubstrings.stream().noneMatch(title::contains)) {
// no bad words :D
}
This isn't very efficient if title is a long string (but titles usually aren't supposed to be long, I suppose).
If you want an efficient solution and you have many bannedSubstrings, I guess, it would be faster to join them into single regexp like this:
Pattern badWords = Pattern.compile(bannedSubstrings.stream().map(Pattern::quote)
.collect(Collectors.joining("|")));
Then use it like this:
if (badWords.matcher(title).find()) {
...
}
This should build a prefix tree from your substrings, so scanning will be significantly faster. If performance is not the concern in your case, use other answers.
I suppose you are looking for something like this:
if(bannedSubstrings.stream().anyMatch(title::contains)){
}
The answer you've selected is pretty good, but for real performance you'd probably be better off pre-compiling the list of bad words into a regex.
public class BannedWordChecker {
public final Pattern bannedWords;
public BannedWordChecker(Collection<String> bannedWords) {
this.bannedWords =
Pattern.compile(
bannedWords.stream()
.map(Pattern::quote)
.collect(Collectors.joining("|")));
}
public boolean containsBannedWords(String string) {
return bannedWords.matcher(string).find();
}
}
I am doing a java code inspection. Here is a function (snippet):
String getValue() {
String res;
StringBuilder strBuilder = new StringBuilder();
// More code here that sets strBuilder
return res = strBuilder.toString();
}
First there is a warning that the value of res is not used. Secondly I don't understand the return. Why don't they just return( strBuilder.toString() ). Is there some sort of advantage?
res is not used, so there is no reason to return like that. You can remove it:
String getValue() {
StringBuilder bs = new StringBuilder();
//
// More code here that sets sb
return bs.toString();
}
That sort of code can sometimes result from incomplete removal of debug artifacts:
String getValue() {
String res;
StringBuilder bs = new StringBuilder();
//
// More code here that sets sb
res = bs.toString();
// Test and/or display res here
return res;
}
It certainly seems like a good candidate for the next round of refactoring and clean-up.
Just guessing, but some (most?) IDEs don't allow you to directly inspect the value of function returns. With this scheme, you could put a breakpoint at the end of the method, and mouse over "res" to get the return value.
You're absolutely right; assignment to res makes no sense; return bs.toString(); would do the the same.
P.S. +1 for not ignoring compiler warnings.
You cant do either
String res = strBuilder.toString();
return res ;
Or directly,
return strBuilder.toString();
Now If you want to know about benefits as you asked Is there any benefit, i always prefer directly return. My personal logic is simple as
You gonna write one line less code !!! (declaring variables allover is not a good feeling to me and also you don't have to think about the name of the variable, conflicts etc.. those silly matter )
The value will not be stored in memory and wait for the GC to collect it. SO, less memory see.....
Fast write to a variable and then read from it and return ..... more read/write isn't it?
Those things are nothing big, I had to say as you asked
Can also be written as:
String getValue() {
return new StringBuilder().toString();
}
Does anybody know if there is any easy way within Java to prefix one string onto multiple other strings?
For example, if I have the following snippet of Java code ;
String includeDir = "/usr/local/boost-1.52.0/include";
ArrayList<String> filenamesRelative = new ArrayList<String>(),
filenamesAbsolute = new ArrayList<String>();
filenamesRelative.add("/boost/aligned_storage.hpp");
filenamesRelative.add("/boost/any.hpp");
I would like to be able to prefix the value of the variable 'includeDir', i.e. "/usr/local/boost-1.52.0/include", onto the front of each value in the ArrayList filenamesRelative.
Ideally, I would like to be able to do something like the following ;
filenameAbsolute = filenamesRelative.prefixAll(includeDir);
I don't necessarily have to use ArrayLists in the solution; I have just used them above for illustrative purposes.
From memory, you can do something like this rather easily in C++ using the STL, however my current working knowledge of Java isn't all that good unfortunately :(
Thanks in advance for any assistance.
I dont know of a method in the API. but its so simple just create your own. Something like:
List<String> filenameAbsolute = new ArrayList<String>();
for ( String file: filenamesRelative ) {
filenameAbsolute.add(prefix + file);
}
Do it like this:
ArrayList<String> prefixAll(ArrayList<String> filenamesRelative)
{
ArrayList<String> filenamesAbsolute = new ArrayList<String>();
String includeDir = "/usr/local/boost-1.52.0/include";
for ( String file: filenamesRelative ) {
filenameAbsolute.add(includeDir + file);
}//for
return filenameAbsolute;
}//prefixAll()
I'm sure there must be a standard way to do this, but my attempts to search Stackoverflow have failed.
I have a method like:
public void processSomeWidgetsForUser(int userItemId) {
Iterator<Widgets> iter = allWidgets.values().iterator();
while(iter.hasNext()) {
Widget thisWidget = iter.next();
if (userItemId == -1 || thisWidget.getUsersItemId() == userItemId) {
widget.process();
}
}
}
As you can see -1 is a "special value" meaning process all. Doing this saves repeating the loop code in another method called processSomeWidgetsForAllUsers.
But I dislike special values like this because they are easy to misuse or misunderstand, which is exactly the situation what I'm having to fix now (where someone thought -1 meant something else).
I can only think of two ways to improve this.
have a constant, containing -1 called something like
Widget.ALLWIDGETS which at least is self-documenting, but doesn't
stop code from using a -1 (if someone integrates old code in, for
example)
change the method to take a list of all user ids to
process, which can be empty, but that doesn't seem great
performance-wise (would need to retrieve all user ids first and then loop through
removing. Also what happens if the number of widgets in the list changes between
retreiving the ids and removing
Is there a better way? I'm sure I'm missing something obvious.
The above code has been changed slightly, so may not compile, but you should get the gist.
Although somewhat redundant, a fairly neat self-documenting approach could be to have 3 methods rather than one;
Make your original method private, and make one small change which would be to add your static final int EXECUTE_ALL = -1 and use that in your original method, then add the two new methods;
public void processWidget(int wID) throws IllegalArgumentException {
if(wID == EXECUTE_ALL) throw new IllegalArgumentException();
originalMethod(wID);
}
public void processAllWidgets() {
originalMethod(EXECUTE_ALL);
}
It makes your class a little more cluttered, but as far as the exposed methods go, it is clearer and hopefully foolproof. You could alter it not to throw an exception and just ignore any invalid ids, that just depends on your situation.
This approach of course has the major downside that it changes how the class appears to other classes, breaking everything that currently uses the, now private, originalMethod().
Number 1 would work very nicely. Be sure to document what the variable is though, so future coders (possibly yourself) know what it means.
/**This is the explanation for the below variable*/
public final static int ALL_WIDGETS = -1;
Have an external method like so:
static boolean idRepresentsAll(int id) {
return id == -1;
}
In this case, if you decide to replace it with a different mechanism, you only replace your magic number one place in your code.
At the very least, you would want to do something like this:
public static final int ID_REPRESENTING_ALL = -1;
You can change the method signature to accept a boolean for when you want to process them all.
public void processSomeWidgets(boolean doAll, int userItemId) {
Iterator<Widgets> iter = allWidgets.values().iterator();
while(iter.hasNext()) {
Widget thisWidget = iter.next();
if (doAll || thisWidget.getUsersItemId() == userItemId) {
widget.process();
}
}
}
This makes it more explicit, and easier to read in my opinion as there are no special values.
Given a string like so:
Hello {FIRST_NAME}, this is a personalized message for you.
Where FIRST_NAME is an arbitrary token (a key in a map passed to the method), to write a routine which would turn that string into:
Hello Jim, this is a personalized message for you.
given a map with an entry FIRST_NAME -> Jim.
It would seem that StringTokenizer is the most straight forward approach, but the Javadocs really say you should prefer to use the regex aproach. How would you do that in a regex based solution?
Thanks everyone for the answers!
Gizmo's answer was definitely out of the box, and a great solution, but unfortunately not appropriate as the format can't be limited to what the Formatter class does in this case.
Adam Paynter really got to the heart of the matter, with the right pattern.
Peter Nix and Sean Bright had a great workaround to avoid all of the complexities of the regex, but I needed to raise some errors if there were bad tokens, which that didn't do.
But in terms of both doing a regex and a reasonable replace loop, this is the answer I came up with (with a little help from Google and the existing answer, including Sean Bright's comment about how to use group(1) vs group()):
private static Pattern tokenPattern = Pattern.compile("\\{([^}]*)\\}");
public static String process(String template, Map<String, Object> params) {
StringBuffer sb = new StringBuffer();
Matcher myMatcher = tokenPattern.matcher(template);
while (myMatcher.find()) {
String field = myMatcher.group(1);
myMatcher.appendReplacement(sb, "");
sb.append(doParameter(field, params));
}
myMatcher.appendTail(sb);
return sb.toString();
}
Where doParameter gets the value out of the map and converts it to a string and throws an exception if it isn't there.
Note also I changed the pattern to find empty braces (i.e. {}), as that is an error condition explicitly checked for.
EDIT: Note that appendReplacement is not agnostic about the content of the string. Per the javadocs, it recognizes $ and backslash as a special character, so I added some escaping to handle that to the sample above. Not done in the most performance conscious way, but in my case it isn't a big enough deal to be worth attempting to micro-optimize the string creations.
Thanks to the comment from Alan M, this can be made even simpler to avoid the special character issues of appendReplacement.
Well, I would rather use String.format(), or better MessageFormat.
String.replaceAll("{FIRST_NAME}", actualName);
Check out the javadocs for it here.
Try this:
Note: The author's final solution builds upon this sample and is much more concise.
public class TokenReplacer {
private Pattern tokenPattern;
public TokenReplacer() {
tokenPattern = Pattern.compile("\\{([^}]+)\\}");
}
public String replaceTokens(String text, Map<String, String> valuesByKey) {
StringBuilder output = new StringBuilder();
Matcher tokenMatcher = tokenPattern.matcher(text);
int cursor = 0;
while (tokenMatcher.find()) {
// A token is defined as a sequence of the format "{...}".
// A key is defined as the content between the brackets.
int tokenStart = tokenMatcher.start();
int tokenEnd = tokenMatcher.end();
int keyStart = tokenMatcher.start(1);
int keyEnd = tokenMatcher.end(1);
output.append(text.substring(cursor, tokenStart));
String token = text.substring(tokenStart, tokenEnd);
String key = text.substring(keyStart, keyEnd);
if (valuesByKey.containsKey(key)) {
String value = valuesByKey.get(key);
output.append(value);
} else {
output.append(token);
}
cursor = tokenEnd;
}
output.append(text.substring(cursor));
return output.toString();
}
}
With import java.util.regex.*:
Pattern p = Pattern.compile("{([^{}]*)}");
Matcher m = p.matcher(line); // line being "Hello, {FIRST_NAME}..."
while (m.find) {
String key = m.group(1);
if (map.containsKey(key)) {
String value= map.get(key);
m.replaceFirst(value);
}
}
So, the regex is recommended because it can easily identify the places that require substitution in the string, as well as extracting the name of the key for substitution. It's much more efficient than breaking the whole string.
You'll probably want to loop with the Matcher line inside and the Pattern line outside, so you can replace all lines. The pattern never needs to be recompiled, and it's more efficient to avoid doing so unnecessarily.
The most straight forward would seem to be something along the lines of this:
public static void main(String[] args) {
String tokenString = "Hello {FIRST_NAME}, this is a personalized message for you.";
Map<String, String> tokenMap = new HashMap<String, String>();
tokenMap.put("{FIRST_NAME}", "Jim");
String transformedString = tokenString;
for (String token : tokenMap.keySet()) {
transformedString = transformedString.replace(token, tokenMap.get(token));
}
System.out.println("New String: " + transformedString);
}
It loops through all your tokens and replaces every token with what you need, and uses the standard String method for replacement, thus skipping the whole RegEx frustrations.
Depending on how ridiculously complex your string is, you could try using a more serious string templating language, like Velocity. In Velocity's case, you'd do something like this:
Velocity.init();
VelocityContext context = new VelocityContext();
context.put( "name", "Bob" );
StringWriter output = new StringWriter();
Velocity.evaluate( context, output, "",
"Hello, #name, this is a personalized message for you.");
System.out.println(output.toString());
But that is likely overkill if you only want to replace one or two values.
import java.util.HashMap;
public class ReplaceTest {
public static void main(String[] args) {
HashMap<String, String> map = new HashMap<String, String>();
map.put("FIRST_NAME", "Jim");
map.put("LAST_NAME", "Johnson");
map.put("PHONE", "410-555-1212");
String s = "Hello {FIRST_NAME} {LAST_NAME}, this is a personalized message for you.";
for (String key : map.keySet()) {
s = s.replaceAll("\\{" + key + "\\}", map.get(key));
}
System.out.println(s);
}
}
The docs mean that you should prefer writing a regex-based tokenizer, IIRC. What might work better for you is a standard regex search-replace.
Generally we'd use MessageFormat in a case like this, coupled with loading the actual message text from a ResourceBundle. This gives you the added benefit of being G10N friendly.