问题
I'm confused a bit. I couldn't find the answer anywhere ;(
I've got an String array:
String[] arr = ["1", "2", "3"];
then I convert it to a string by:
String str = Arrays.toString(arr);
System.out.println(str);
I expected to get the string "123", but I got the string "[1,2,3]" instead.
How could I do it in java? I'm using Eclipse IDE
回答1:
Use StringBuilder instead of StringBuffer, because it is faster than StringBuffer.
Sample code
String[] strArr = {"1", "2", "3"};
StringBuilder strBuilder = new StringBuilder();
for (int i = 0; i < strArr.length; i++) {
strBuilder.append(strArr[i]);
}
String newString = strBuilder.toString();
Here's why this is a better solution to using string concatenation: When you concatenate 2 strings, a new string object is created and character by character copy is performed.
Effectively meaning that the code complexity would be the order of the squared of the size of your array!
(1+2+3+ ... n which is the number of characters copied per iteration).
StringBuilder would do the 'copying to a string' only once in this case reducing the complexity to O(n).
回答2:
Simple answer:
Arrays.toString(arr);
回答3:
Arrays.toString(arr);
output is [1,2,3] and you storing it to your string . and printing it so you get output [1,2,3].
If you want to get output 123 try this:
public static void main(String[] args) {
String[] arr= {"1","2","3"};
String output ="";
for(String str: arr)
output=output+str;
System.out.println(output);
}
Output:
123
回答4:
Arrays.toString: (from the API, at least for the Object[] version of it)
public static String toString(Object[] a) {
if (a == null)
return "null";
int iMax = a.length - 1;
if (iMax == -1)
return "[]";
StringBuilder b = new StringBuilder();
b.append('[');
for (int i = 0; ; i++) {
b.append(String.valueOf(a[i]));
if (i == iMax)
return b.append(']').toString();
b.append(", ");
}
}
So that means it inserts the [ at the start, the ] at the end, and the , between elements.
If you want it without those characters: (StringBuilder is faster than the below, but it can't be the small amount of code)
String str = "";
for (String i:arr)
str += i;
System.out.println(str);
Side note:
String[] arr[3]= [1,2,3] won't compile.
Presumably you wanted: String[] arr = {"1", "2", "3"};
回答5:
Use the Arrays.toString() function. It keeps your code short and readable. It uses a string builder internally, thus, it's also efficient. To get rid of the extra characters, you might chose to eliminate them using the String.replace() function, which, admittedly, reduces readability again.
String str = Arrays.toString(arr).replaceAll(", |\\[|\\]", "");
This is similar to the answer of Tris Nefzger, but without the lengthy substring construction to get rid of the square brackets.
Explanation of the Regex: "|" means any of ", " and "[" and "]". The "\\" tells the Java String that we are not meaning some special character (like a new line "\n" or a tab "\t") but a real backslash "\". So instead of "\\[", the Regex interpreter reads "\[", which tells it that we mean a literal square bracket and do not want to use it as part of the Regex language (for instance, "[^3]*" denotes any number of characters, but none of them should be "3").
回答6:
Do it java 8 way in just 1 line:
String.join("", arr);
回答7:
Guava has Joiner utility to resolve this issue:
Example:
String joinWithoutSeparator = Joiner.on("").join(1, 2, 3); // returns "123"
String joinWithSeparator = Joiner.on(",").join(1, 2, 3); // returns "1,2,3"
回答8:
I have just written the following:
public static String toDelimitedString(int[] ids, String delimiter)
{
StringBuffer strb = new StringBuffer();
for (int id : ids)
{
strb.append(String.valueOf(id) + delimiter);
}
return strb.substring(0, strb.length() - delimiter.length());
}
回答9:
Arrays.toString is formatting the output (added the brackets and commas). you should implement your own method of toString.
public String toString(String[] arr){
String result = "";
for(String s : arr)
result+=s;
return result;
}
[edit] Stringbuilder is better though. see above.
回答10:
For Spring based projects:
org.springframework.util.StringUtils.arrayToDelimitedString(Object[] arr, String delim)
For Apache Commons users, set of nice join methods:
org.apache.commons.lang.StringUtils.join(Object[] array, char separator)
回答11:
Using Guava's Joiner (which in r18 internally uses StringBuilder)
String[] arr= {"1","2","3"};
Joiner noSpaceJoiner = Joiner.on("");
noSpaceJoiner.join(arr))
Joiner is useful because it is thread-safe and immutable and can be reused in many places without having to duplicate code. In my opinion it also is more readable.
Using Java 8's Stream support, we can also reduce this down to a one-liner.
String concat = Stream.of(arr).collect(Collectors.joining());
Both outputs in this case are 123
回答12:
This is a little code of convert string array to string without [ or ] or ,
String[] strArray = new String[]{"Java", "String", "Array", "To", "String", "Example"};
String str = Arrays.toString(strArray);
str = str.substring(1, str.length()-1).replaceAll(",", "");
- First convert array to string.
- Second get text from x to y position.
- third replace all ',' with ""
回答13:
take a look at generic method to print all elements in an array
but in short, the Arrays.toString(arr) is just a easy way of printing the content of a primative array.
回答14:
Object class has toString method. All other classes extending it overrides the toString method so in for arrays also toString is overrided in this way. So if you want your output in your way you need to create your own method by which you will get your desired result.
str="";
for (Integer i:arr){
str+=i.toString();
}
Hope this helps
refer Why does the toString method in java not seem to work for an array
回答15:
Here is a way to do it: Arrays.toString(array).substring(1,(3*array.length-1)).replaceAll(", ","");
Here is a demo class:
package arraytostring.demo;
import java.util.Arrays;
public class Array2String {
public static void main(String[] args) {
String[] array = { "1", "2", "3", "4", "5", "6", "7" };
System.out.println(array2String(array));
// output is: 1234567
}
public static String array2String(String[] array) {
return Arrays.toString(array).substring(1, (3 * array.length - 1))
.replaceAll(", ", "");
}
}
Scala makes this easier, cleaner and safer:
scala> val a = Array("1", "2", "3")
a: Array[String] = Array(1, 2, 3)
scala> val aString = a.mkString
aString: String = 123
scala> println(aString)
123
回答16:
For those who develop in Android, use TextUtils.
String items = TextUtils.join("", arr);
Assuming arr is of type String[] arr= {"1","2","3"};
The output would be 123
回答17:
Example using Java 8.
String[] arr = {"1", "2", "3"};
String join = String.join("", arr);
I hope that helps
回答18:
Arrays.toString() can be used to convert String Array to String. The extra characters can be removed by using Regex expressions or simply by using replace method.
Arrays.toString(strArray).replace(",", "").replace("[", "").replace("]", "");
Java 8 has introduced new method for String join public static String join(CharSequence delimiter, CharSequence... elements)
String.join("", strArray);
回答19:
String newString= Arrays.toString(oldString).replace("[","").replace("]","").replace(",","").trim();
来源：https://stackoverflow.com/questions/14957964/concatenating-elements-in-an-array-to-a-string