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multiple replaces in Java

I am using Java 1.8. I have a large amount of text in a buffer. The text has some occurrences likt the following:
"... {NAME} is going to {PLACE}...", blah blah blah.
Then I have two arrays: "{NAME};{PLACE}" and "Mick Jagger;A Gogo", etc. (These are just examples).
I make a Map replacements of these such as
{NAME};Mick Jagger
{PLACE};A Gogo
So I want to do all the replacements. In this case there is only 2 so it is not so cumbersome. Say my original text is in txt:
for (EntrySet<String, String> entry : replacements.entrySet()) {
txt = txt.replace(entry.getKey(), entry.getValue());
}
You can imaging if there are like a lot of replacements this could take a long time.
Is there some better way to make all the replacements, or is this basically what you would do?

To avoid calling String.replace many times, you can use a regex which matches every replacement-key. You can then iteratively scan for the next replacement-key in the input string using a loop, and find its substitute using Map.get:
import java.util.Collection;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
public class ReplaceMap {
private final Pattern p;
public ReplaceMap(Collection<String> keys) {
this.p = Pattern.compile(keys.stream()
.map(ReplaceMap::escapeRegex)
.collect(Collectors.joining("|")));
}
public String replace(String input, Map<String,String> subs) {
Matcher m = p.matcher(input);
StringBuilder out = new StringBuilder();
int i = 0;
while(m.find()) {
out.append(input.substring(i, m.start()));
String key = m.group(0);
out.append(subs.get(key));
i = m.end();
}
out.append(input.substring(i));
return out.toString();
}
// from https://stackoverflow.com/a/25853507/12299000
private static Pattern SPECIAL_REGEX_CHARS = Pattern.compile("[{}()\\[\\].+*?^$\\\\|]");
private static String escapeRegex(String s) {
return SPECIAL_REGEX_CHARS.matcher(s).replaceAll("\\\\$0");
}
}
Usage:
> Map<String,String> subs = new HashMap<>();
> subs.put("{NAME}", "Alice");
> subs.put("{PLACE}", "Wonderland");
> ReplaceMap r = new ReplaceMap(subs.keySet());
> r.replace("Hello, {NAME} in {PLACE}.", subs)
"Hello, Alice in Wonderland." (String)
This solution should be about as efficient regardless of how many replacement key/value pairs there are in the subs map.

I'd suggest reading file line by line (using NIO) and for each line you can iterate your map and replace it if you have something. So in this case you need to go over your big data only once

Sorting a String by its 6 first characters

I have IDs with the following format : XXXXXXYYY00000
What I am trying to do is to get a single string organised alphabetically by the 6 first characters (the 6 x's (they can be any character)) with each new ID separated by a new line character
For example :
AOPSIKPMI23495 would go before BWLMBEPMI00001
What I have so far is :
String = String + this.ID + "\n";
And I have no idea how to approach my problem in order to solve it.
My question is the following : How do I organise my IDs alphabetically, only by its first 6 characters (meaning if there's a tie with the 6 first characters, it still shouldn't resolve it with the next 3 characters) and still keeping my String ?

you can sort the list by the first 6 characters and then use Collectors.joining to separate each string with a "\n" delimiter.
String result = myList.stream().sorted(Comparator.comparing(e -> e.substring(0,6)))
.collect(Collectors.joining("\n"));

You can simply implement a comparator just to compare the first 6 characters:
class FirstSixCharComparator implements Comparator<String> {
#Override
public int compare(String a, String b) {
return a.substring(0,6)compareTo(b.substring(0,6));
}
}
Then use the comparator to perform a sort:
Collections.sort(list, new FirstSixCharComparator<String>()); //for collections
Arrays.sort(array, new FirstSixCharComparator<String>()); //for arrays

this piece of code should solve your problem , if its not then we can write comparator kind of stuff to satisfy whatever requirement you have of it.
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Sample {
public static void main(String[] args) {
List<String> words = new ArrayList<String>();
words.add("AOPSIKDDD23495");
words.add("BWLMBEPMI00001");
Collections.sort(words);
System.out.println(words);
}
}

Built in method for removing duplicates in a string array

Is there a java built-in method for removing duplicates ? (array of strings)
Maybe using a Set ? in this case how can I use it ?
Thanks

Instead of an array of string, you can directly use a set (in this case all elements in set will always be unique of that type) but if you only want to use array of strings , you can use the following to save array to set then save it back.
import java.util.Arrays;
import java.util.HashSet;
public class HelloWorld{
public static void main(String []args)
{
String dupArray[] = {"hi","hello","hi"};
dupArray=removeDuplicates(dupArray);
for(String s: dupArray)
System.out.println(s);
}
public static String[] removeDuplicates(String []dupArray)
{
HashSet<String> mySet = new HashSet<String>(Arrays.asList(dupArray));
dupArray = new String[mySet.size()];
mySet.toArray(dupArray);
return dupArray;
}
}

Promblem finding empty elements in a comma seperated data

import java.util.ArrayList;
import java.util.StringTokenizer;
public class test {
public static void main(String args[]) {
ArrayList<String> data = new ArrayList<String>();
String s = "a,b,c,d,e,f,g";
StringTokenizer st = new StringTokenizer(s,",");
while(st.hasMoreTokens()){
data.add(st.nextToken());
}
System.out.println(data);
}
}
Problem in finding empty elements in a CSV data
the above code works well when the data is complete. If some data is missing it fails to detect the empty data.
ex:
Complete DATA : a,b,c,d,e,f,g
if a,d,e,g are removed
New DATA : ,b,c,,,f,
4 data missing!!
I need a way to put this data into ArrayList with null or "" values for empty data

You can use Guava Splitter to do that:
import com.google.common.base.Splitter;
public class Example
{
private static final Splitter SPLITTER = Splitter.on(",").trimResults();
public List<String> split(String singleLine) {
return SPLITTER.split(singleLine);
}
}

I'm sure there are more elegant solutions, but a simple one would be to use split() function:
public static void main(String args[]) {
ArrayList<String> data = new ArrayList<String>();
String s = ",b,c,,,f,";
//create an array of strings, using "," as a delimiter
//if there is no letter between commas, an empty string will be
//placed in strings[] instead
String[] strings = s.split(",", -1);
for (String ss : strings) {
data.add(ss);
}
System.out.println(data);
}

What's the best way to build a string of delimited items in Java?

While working in a Java app, I recently needed to assemble a comma-delimited list of values to pass to another web service without knowing how many elements there would be in advance. The best I could come up with off the top of my head was something like this:
public String appendWithDelimiter( String original, String addition, String delimiter ) {
if ( original.equals( "" ) ) {
return addition;
} else {
return original + delimiter + addition;
}
}
String parameterString = "";
if ( condition ) parameterString = appendWithDelimiter( parameterString, "elementName", "," );
if ( anotherCondition ) parameterString = appendWithDelimiter( parameterString, "anotherElementName", "," );
I realize this isn't particularly efficient, since there are strings being created all over the place, but I was going for clarity more than optimization.
In Ruby, I can do something like this instead, which feels much more elegant:
parameterArray = [];
parameterArray << "elementName" if condition;
parameterArray << "anotherElementName" if anotherCondition;
parameterString = parameterArray.join(",");
But since Java lacks a join command, I couldn't figure out anything equivalent.
So, what's the best way to do this in Java?

Pre Java 8:
Apache's commons lang is your friend here - it provides a join method very similar to the one you refer to in Ruby:
StringUtils.join(java.lang.Iterable,char)
Java 8:
Java 8 provides joining out of the box via StringJoiner and String.join(). The snippets below show how you can use them:
StringJoiner
StringJoiner joiner = new StringJoiner(",");
joiner.add("01").add("02").add("03");
String joinedString = joiner.toString(); // "01,02,03"
String.join(CharSequence delimiter, CharSequence... elements))
String joinedString = String.join(" - ", "04", "05", "06"); // "04 - 05 - 06"
String.join(CharSequence delimiter, Iterable<? extends CharSequence> elements)
List<String> strings = new LinkedList<>();
strings.add("Java");strings.add("is");
strings.add("cool");
String message = String.join(" ", strings);
//message returned is: "Java is cool"

You could write a little join-style utility method that works on java.util.Lists
public static String join(List<String> list, String delim) {
StringBuilder sb = new StringBuilder();
String loopDelim = "";
for(String s : list) {
sb.append(loopDelim);
sb.append(s);
loopDelim = delim;
}
return sb.toString();
}
Then use it like so:
List<String> list = new ArrayList<String>();
if( condition ) list.add("elementName");
if( anotherCondition ) list.add("anotherElementName");
join(list, ",");

In the case of Android, the StringUtils class from commons isn't available, so for this I used
android.text.TextUtils.join(CharSequence delimiter, Iterable tokens)
http://developer.android.com/reference/android/text/TextUtils.html

The Google's Guava library has com.google.common.base.Joiner class which helps to solve such tasks.
Samples:
"My pets are: " + Joiner.on(", ").join(Arrays.asList("rabbit", "parrot", "dog"));
// returns "My pets are: rabbit, parrot, dog"
Joiner.on(" AND ").join(Arrays.asList("field1=1" , "field2=2", "field3=3"));
// returns "field1=1 AND field2=2 AND field3=3"
Joiner.on(",").skipNulls().join(Arrays.asList("London", "Moscow", null, "New York", null, "Paris"));
// returns "London,Moscow,New York,Paris"
Joiner.on(", ").useForNull("Team held a draw").join(Arrays.asList("FC Barcelona", "FC Bayern", null, null, "Chelsea FC", "AC Milan"));
// returns "FC Barcelona, FC Bayern, Team held a draw, Team held a draw, Chelsea FC, AC Milan"
Here is an article about Guava's string utilities.

In Java 8 you can use String.join():
List<String> list = Arrays.asList("foo", "bar", "baz");
String joined = String.join(" and ", list); // "foo and bar and baz"
Also have a look at this answer for a Stream API example.

in Java 8 you can do this like:
list.stream().map(Object::toString)
.collect(Collectors.joining(delimiter));
if list has nulls you can use:
list.stream().map(String::valueOf)
.collect(Collectors.joining(delimiter))
it also supports prefix and suffix:
list.stream().map(String::valueOf)
.collect(Collectors.joining(delimiter, prefix, suffix));

You can generalize it, but there's no join in Java, as you well say.
This might work better.
public static String join(Iterable<? extends CharSequence> s, String delimiter) {
Iterator<? extends CharSequence> iter = s.iterator();
if (!iter.hasNext()) return "";
StringBuilder buffer = new StringBuilder(iter.next());
while (iter.hasNext()) buffer.append(delimiter).append(iter.next());
return buffer.toString();
}

Use an approach based on java.lang.StringBuilder! ("A mutable sequence of characters. ")
Like you mentioned, all those string concatenations are creating Strings all over. StringBuilder won't do that.
Why StringBuilder instead of StringBuffer? From the StringBuilder javadoc:
Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.

I would use Google Collections. There is a nice Join facility.
http://google-collections.googlecode.com/svn/trunk/javadoc/index.html?com/google/common/base/Join.html
But if I wanted to write it on my own,
package util;
import java.util.ArrayList;
import java.util.Iterable;
import java.util.Collections;
import java.util.Iterator;
public class Utils {
// accept a collection of objects, since all objects have toString()
public static String join(String delimiter, Iterable<? extends Object> objs) {
if (objs.isEmpty()) {
return "";
}
Iterator<? extends Object> iter = objs.iterator();
StringBuilder buffer = new StringBuilder();
buffer.append(iter.next());
while (iter.hasNext()) {
buffer.append(delimiter).append(iter.next());
}
return buffer.toString();
}
// for convenience
public static String join(String delimiter, Object... objs) {
ArrayList<Object> list = new ArrayList<Object>();
Collections.addAll(list, objs);
return join(delimiter, list);
}
}
I think it works better with an object collection, since now you don't have to convert your objects to strings before you join them.

Apache commons StringUtils class has a join method.

Java 8
stringCollection.stream().collect(Collectors.joining(", "));

Java 8 Native Type
List<Integer> example;
example.add(1);
example.add(2);
example.add(3);
...
example.stream().collect(Collectors.joining(","));
Java 8 Custom Object:
List<Person> person;
...
person.stream().map(Person::getAge).collect(Collectors.joining(","));

Use StringBuilder and class Separator
StringBuilder buf = new StringBuilder();
Separator sep = new Separator(", ");
for (String each : list) {
buf.append(sep).append(each);
}
Separator wraps a delimiter. The delimiter is returned by Separator's toString method, unless on the first call which returns the empty string!
Source code for class Separator
public class Separator {
private boolean skipFirst;
private final String value;
public Separator() {
this(", ");
}
public Separator(String value) {
this.value = value;
this.skipFirst = true;
}
public void reset() {
skipFirst = true;
}
public String toString() {
String sep = skipFirst ? "" : value;
skipFirst = false;
return sep;
}
}

You can use Java's StringBuilder type for this. There's also StringBuffer, but it contains extra thread safety logic that is often unnecessary.

And a minimal one (if you don't want to include Apache Commons or Gauva into project dependencies just for the sake of joining strings)
/**
*
* #param delim : String that should be kept in between the parts
* #param parts : parts that needs to be joined
* #return a String that's formed by joining the parts
*/
private static final String join(String delim, String... parts) {
StringBuilder builder = new StringBuilder();
for (int i = 0; i < parts.length - 1; i++) {
builder.append(parts[i]).append(delim);
}
if(parts.length > 0){
builder.append(parts[parts.length - 1]);
}
return builder.toString();
}

Why not write your own join() method? It would take as parameters collection of Strings and a delimiter String. Within the method iterate over the collection and build up your result in a StringBuffer.

If you are using Spring MVC then you can try following steps.
import org.springframework.util.StringUtils;
List<String> groupIds = new List<String>;
groupIds.add("a");
groupIds.add("b");
groupIds.add("c");
String csv = StringUtils.arrayToCommaDelimitedString(groupIds.toArray());
It will result to a,b,c

If you're using Eclipse Collections, you can use makeString() or appendString().
makeString() returns a String representation, similar to toString().
It has three forms
makeString(start, separator, end)
makeString(separator) defaults start and end to empty strings
makeString() defaults the separator to ", " (comma and space)
Code example:
MutableList<Integer> list = FastList.newListWith(1, 2, 3);
assertEquals("[1/2/3]", list.makeString("[", "/", "]"));
assertEquals("1/2/3", list.makeString("/"));
assertEquals("1, 2, 3", list.makeString());
assertEquals(list.toString(), list.makeString("[", ", ", "]"));
appendString() is similar to makeString(), but it appends to an Appendable (like StringBuilder) and is void. It has the same three forms, with an additional first argument, the Appendable.
MutableList<Integer> list = FastList.newListWith(1, 2, 3);
Appendable appendable = new StringBuilder();
list.appendString(appendable, "[", "/", "]");
assertEquals("[1/2/3]", appendable.toString());
If you can't convert your collection to an Eclipse Collections type, just adapt it with the relevant adapter.
List<Object> list = ...;
ListAdapter.adapt(list).makeString(",");
Note: I am a committer for Eclipse collections.

You should probably use a StringBuilder with the append method to construct your result, but otherwise this is as good of a solution as Java has to offer.

Why don't you do in Java the same thing you are doing in ruby, that is creating the delimiter separated string only after you've added all the pieces to the array?
ArrayList<String> parms = new ArrayList<String>();
if (someCondition) parms.add("someString");
if (anotherCondition) parms.add("someOtherString");
// ...
String sep = ""; StringBuffer b = new StringBuffer();
for (String p: parms) {
b.append(sep);
b.append(p);
sep = "yourDelimiter";
}
You may want to move that for loop in a separate helper method, and also use StringBuilder instead of StringBuffer...
Edit: fixed the order of appends.

With Java 5 variable args, so you don't have to stuff all your strings into a collection or array explicitly:
import junit.framework.Assert;
import org.junit.Test;
public class StringUtil
{
public static String join(String delim, String... strings)
{
StringBuilder builder = new StringBuilder();
if (strings != null)
{
for (String str : strings)
{
if (builder.length() > 0)
{
builder.append(delim).append(" ");
}
builder.append(str);
}
}
return builder.toString();
}
#Test
public void joinTest()
{
Assert.assertEquals("", StringUtil.join(",", null));
Assert.assertEquals("", StringUtil.join(",", ""));
Assert.assertEquals("", StringUtil.join(",", new String[0]));
Assert.assertEquals("test", StringUtil.join(",", "test"));
Assert.assertEquals("foo, bar", StringUtil.join(",", "foo", "bar"));
Assert.assertEquals("foo, bar, x", StringUtil.join(",", "foo", "bar", "x"));
}
}

For those who are in a Spring context their StringUtils class is useful as well:
There are many useful shortcuts like:
collectionToCommaDelimitedString(Collection coll)
collectionToDelimitedString(Collection coll, String delim)
arrayToDelimitedString(Object[] arr, String delim)
and many others.
This can be helpful if you are not already using Java 8 and you are already in a Spring context.
I prefer it against the Apache Commons (although very good as well) for the Collection support which is easier like this:
// Encoding Set<String> to String delimited
String asString = org.springframework.util.StringUtils.collectionToDelimitedString(codes, ";");
// Decoding String delimited to Set
Set<String> collection = org.springframework.util.StringUtils.commaDelimitedListToSet(asString);

You can try something like this:
StringBuilder sb = new StringBuilder();
if (condition) { sb.append("elementName").append(","); }
if (anotherCondition) { sb.append("anotherElementName").append(","); }
String parameterString = sb.toString();

So basically something like this:
public static String appendWithDelimiter(String original, String addition, String delimiter) {
if (original.equals("")) {
return addition;
} else {
StringBuilder sb = new StringBuilder(original.length() + addition.length() + delimiter.length());
sb.append(original);
sb.append(delimiter);
sb.append(addition);
return sb.toString();
}
}

Don't know if this really is any better, but at least it's using StringBuilder, which may be slightly more efficient.
Down below is a more generic approach if you can build up the list of parameters BEFORE doing any parameter delimiting.
// Answers real question
public String appendWithDelimiters(String delimiter, String original, String addition) {
StringBuilder sb = new StringBuilder(original);
if(sb.length()!=0) {
sb.append(delimiter).append(addition);
} else {
sb.append(addition);
}
return sb.toString();
}
// A more generic case.
// ... means a list of indeterminate length of Strings.
public String appendWithDelimitersGeneric(String delimiter, String... strings) {
StringBuilder sb = new StringBuilder();
for (String string : strings) {
if(sb.length()!=0) {
sb.append(delimiter).append(string);
} else {
sb.append(string);
}
}
return sb.toString();
}
public void testAppendWithDelimiters() {
String string = appendWithDelimitersGeneric(",", "string1", "string2", "string3");
}

Your approach is not too bad, but you should use a StringBuffer instead of using the + sign. The + has the big disadvantage that a new String instance is being created for each single operation. The longer your string gets, the bigger the overhead. So using a StringBuffer should be the fastest way:
public StringBuffer appendWithDelimiter( StringBuffer original, String addition, String delimiter ) {
if ( original == null ) {
StringBuffer buffer = new StringBuffer();
buffer.append(addition);
return buffer;
} else {
buffer.append(delimiter);
buffer.append(addition);
return original;
}
}
After you have finished creating your string simply call toString() on the returned StringBuffer.

Instead of using string concatenation, you should use StringBuilder if your code is not threaded, and StringBuffer if it is.

You're making this a little more complicated than it has to be. Let's start with the end of your example:
String parameterString = "";
if ( condition ) parameterString = appendWithDelimiter( parameterString, "elementName", "," );
if ( anotherCondition ) parameterString = appendWithDelimiter( parameterString, "anotherElementName", "," );
With the small change of using a StringBuilder instead of a String, this becomes:
StringBuilder parameterString = new StringBuilder();
if (condition) parameterString.append("elementName").append(",");
if (anotherCondition) parameterString.append("anotherElementName").append(",");
...
When you're done (I assume you have to check a few other conditions as well), just make sure you remove the tailing comma with a command like this:
if (parameterString.length() > 0)
parameterString.deleteCharAt(parameterString.length() - 1);
And finally, get the string you want with
parameterString.toString();
You could also replace the "," in the second call to append with a generic delimiter string that can be set to anything. If you have a list of things you know you need to append (non-conditionally), you could put this code inside a method that takes a list of strings.

//Note: if you have access to Java5+,
//use StringBuilder in preference to StringBuffer.
//All that has to be replaced is the class name.
//StringBuffer will work in Java 1.4, though.
appendWithDelimiter( StringBuffer buffer, String addition,
String delimiter ) {
if ( buffer.length() == 0) {
buffer.append(addition);
} else {
buffer.append(delimiter);
buffer.append(addition);
}
}
StringBuffer parameterBuffer = new StringBuffer();
if ( condition ) {
appendWithDelimiter(parameterBuffer, "elementName", "," );
}
if ( anotherCondition ) {
appendWithDelimiter(parameterBuffer, "anotherElementName", "," );
}
//Finally, to return a string representation, call toString() when returning.
return parameterBuffer.toString();

So a couple of things you might do to get the feel that it seems like you're looking for:
1) Extend List class - and add the join method to it. The join method would simply do the work of concatenating and adding the delimiter (which could be a param to the join method)
2) It looks like Java 7 is going to be adding extension methods to java - which allows you just to attach a specific method on to a class: so you could write that join method and add it as an extension method to List or even to Collection.
Solution 1 is probably the only realistic one, now, though since Java 7 isn't out yet :) But it should work just fine.
To use both of these, you'd just add all your items to the List or Collection as usual, and then call the new custom method to 'join' them.