Java function 对于 arrays 像 PHP 的 join()？

Question

I want to join a String[] with a glue string. Is there a function for this?

Answer 1

Starting from Java8 it is possible to use String.join() .

String.join(", ", new String[]{"Hello", "World", "!"})

Generates:

Hello, World, !

Otherwise, Apache Commons Lang has a StringUtils class which has a join function which will join arrays together to make a String .

For example:

StringUtils.join(new String[] {"Hello", "World", "!"}, ", ")

Generates the following String :

Hello, World, !

Answer 2

If you were looking for what to use in android, it is:

String android.text.TextUtils.join(CharSequence delimiter, Object[] tokens)

for example:

String joined = TextUtils.join(";", MyStringArray);

Answer 3

In Java 8 you can use

1) Stream API :

String[] a = new String[] {"a", "b", "c"};
String result = Arrays.stream(a).collect(Collectors.joining(", "));

2) new String.join method: https://stackoverflow.com/a/21756398/466677

3) java.util.StringJoiner class: http://docs.oracle.com/javase/8/docs/api/java/util/StringJoiner.html

Answer 4

You could easily write such a function in about ten lines of code:

String combine(String[] s, String glue)
{
  int k = s.length;
  if ( k == 0 )
  {
    return null;
  }
  StringBuilder out = new StringBuilder();
  out.append( s[0] );
  for ( int x=1; x < k; ++x )
  {
    out.append(glue).append(s[x]);
  }
  return out.toString();
}

Answer 5

A little mod instead of using substring():

//join(String array,delimiter)
public static String join(String r[],String d)
{
        if (r.length == 0) return "";
        StringBuilder sb = new StringBuilder();
        int i;
        for(i=0;i<r.length-1;i++){
            sb.append(r[i]);
            sb.append(d);
        }
        sb.append(r[i]);
        return sb.toString();
}

Answer 6

As with many questions lately, Java 8 to the rescue:

---

Java 8 added a new static method to java.lang.String which does exactly what you want:

public static String join(CharSequence delimeter, CharSequence... elements);

Using it:

String s = String.join(", ", new String[] {"Hello", "World", "!"});

Results in:

"Hello, World, !"

Answer 7

Google guava's library also has this kind of capability . You can see the String[] example also from the API.

As already described in the api, beware of the immutability of the builder methods.

It can accept an array of objects so it'll work in your case. In my previous experience, i tried joining a Stack which is an iterable and it works fine.

Sample from me :

Deque<String> nameStack = new ArrayDeque<>();
nameStack.push("a coder");
nameStack.push("i am");
System.out.println("|" + Joiner.on(' ').skipNulls().join(nameStack) + "|");

prints out : |i am a coder|

Answer 8

If you are using the Spring Framework then you have the StringUtils class:

import static org.springframework.util.StringUtils.arrayToDelimitedString;

arrayToDelimitedString(new String[] {"A", "B", "C"}, "\n");

Answer 9

Given:

String[] a = new String[] { "Hello", "World", "!" };

Then as an alternative to coobird's answer, where the glue is ", ":

Arrays.asList(a).toString().replaceAll("^\\[|\\]$", "")

Or to concatenate with a different string, such as " & ".

Arrays.asList(a).toString().replaceAll(", ", " & ").replaceAll("^\\[|\\]$", "")

However... this one ONLY works if you know that the values in the array or list DO NOT contain the character string ", ".

Answer 10

Not in core, no. A search for "java array join string glue" will give you some code snippets on how to achieve this though.

eg

public static String join(Collection s, String delimiter) {
    StringBuffer buffer = new StringBuffer();
    Iterator iter = s.iterator();
    while (iter.hasNext()) {
        buffer.append(iter.next());
        if (iter.hasNext()) {
            buffer.append(delimiter);
        }
    }
    return buffer.toString();
}

Answer 11

If you've landed here looking for a quick array-to-string conversion, try Arrays.toString() .

Creates a String representation of the Object[] passed. The result is surrounded by brackets ( "[]" ), each element is converted to a String via the String.valueOf(Object) and separated by ", " . If the array is null , then "null" is returned.

Answer 12

Just for the "I've the shortest one" challenge, here are mines ;)

Iterative:

public static String join(String s, Object... a) {
    StringBuilder o = new StringBuilder();
    for (Iterator<Object> i = Arrays.asList(a).iterator(); i.hasNext();)
        o.append(i.next()).append(i.hasNext() ? s : "");
    return o.toString();
}

Recursive:

public static String join(String s, Object... a) {
    return a.length == 0 ? "" : a[0] + (a.length == 1 ? "" : s + join(s, Arrays.copyOfRange(a, 1, a.length)));
}

Answer 13

Nothing built-in that I know of.

Apache Commons Lang has a class called StringUtils which contains many join functions.

Answer 14

This is how I do it.

private String join(String[] input, String delimiter)
{
    StringBuilder sb = new StringBuilder();
    for(String value : input)
    {
        sb.append(value);
        sb.append(delimiter);
    }
    int length = sb.length();
    if(length > 0)
    {
        // Remove the extra delimiter
        sb.setLength(length - delimiter.length());
    }
    return sb.toString();
}

Answer 15

A similar alternative

/**
 * @param delimiter 
 * @param inStr
 * @return String
 */
public static String join(String delimiter, String... inStr)
{
    StringBuilder sb = new StringBuilder();
    if (inStr.length > 0)
    {
        sb.append(inStr[0]);
        for (int i = 1; i < inStr.length; i++)
        {
            sb.append(delimiter);                   
            sb.append(inStr[i]);
        }
    }
    return sb.toString();
}

Answer 16

My spin.

public static String join(Object[] objects, String delimiter) {
  if (objects.length == 0) {
    return "";
  }
  int capacityGuess = (objects.length * objects[0].toString().length())
      + ((objects.length - 1) * delimiter.length());
  StringBuilder ret = new StringBuilder(capacityGuess);
  ret.append(objects[0]);
  for (int i = 1; i < objects.length; i++) {
    ret.append(delimiter);
    ret.append(objects[i]);
  }
  return ret.toString();
}

public static String join(Object... objects) {
  return join(objects, "");
}

Answer 17

Do you like my 3-lines way using only String class's methods?

static String join(String glue, String[] array) {
    String line = "";
    for (String s : array) line += s + glue;
    return (array.length == 0) ? line : line.substring(0, line.length() - glue.length());
}

Answer 18

To get "str1, str2" from "str1", "str2", "" :

Stream.of("str1", "str2", "").filter(str -> !str.isEmpty()).collect(Collectors.joining(", ")); 

Also you can add extra null-check

Answer 19

In case you're using Functional Java library and for some reason can't use Streams from Java 8 (which might be the case when using Android + Retrolambda plugin), here is a functional solution for you:

String joinWithSeparator(List<String> items, String separator) {
    return items
            .bind(id -> list(separator, id))
            .drop(1)
            .foldLeft(
                    (result, item) -> result + item,
                    ""
            );
}

Note that it's not the most efficient approach, but it does work good for small lists.

Answer 20

Whatever approach you choose, be aware of null values in the array. Their string representation is "null" so if it is not your desired behavior, skip null elements.

String[] parts = {"Hello", "World", null, "!"};
Stream.of(parts)
      .filter(Objects::nonNull)
      .collect(Collectors.joining(" "));

Answer 21

As already mentioned, class StringJoiner is also an available option since Java 8:

@NotNull
String stringArrayToCsv(@NotNull String[] data) {
    if (data.length == 0) {return "";}
    StringJoiner joiner = new StringJoiner(", ");
    Iterator<String> itr = Arrays.stream(data).iterator();
    while (itr.hasNext()) {joiner.add(itr.next());}
    return joiner.toString();
}

However, the traditional String.join() is less imports and less code:

@NotNull
String stringArrayToCsv(@NotNull String[] data) {
    if (data.length == 0) {return "";}
    return String.join(", ", data);
}

Answer 22

I do it this way using a StringBuilder:

public static String join(String[] source, String delimiter) {
    if ((null == source) || (source.length < 1)) {
        return "";
    }

    StringBuilder stringbuilder = new StringBuilder();
    for (String s : source) {
        stringbuilder.append(s + delimiter);
    }
    return stringbuilder.toString();
} // join((String[], String)

Answer 23

There is simple shorthand technique I use most of the times..

String op = new String;
for (int i : is) 
{
    op += candidatesArr[i-1]+",";
}
op = op.substring(0, op.length()-1);

Answer 24

java.util.Arrays has an 'asList' method. Together with the java.util.List/ArrayList API this gives you all you need:;

private static String[] join(String[] array1, String[] array2) {

    List<String> list = new ArrayList<String>(Arrays.asList(array1));
    list.addAll(Arrays.asList(array2));
    return list.toArray(new String[0]);
}