Learn Everything about Java String Split Method

1. Understanding the two flavors of the split method

Java.lang.String class contains two flavors of the split() method, which can be used to split a string. Here are the Javadoc definition of these two methods:

public String[] split(String regex) – This method splits the string based on the given regular expression and returns array of strings.

public String[] split(String regex,int limit) –  This method splits the string based on the given regular expression and returns array of strings. The limit parameter controls the number of times the pattern is applied and therefore affects the length of the resulting array. If the limit n is greater than zero then the pattern will be applied at most n – 1 times, the array’s length will be no greater than n, and the array’s last entry will contain all input beyond the last matched delimiter. If n is non-positive then the pattern will be applied as many times as possible and the array can have any length. If n is zero then the pattern will be applied as many times as possible, the array can have any length, and trailing empty strings will be discarded.

So for example if you have a string [“This is a String”] then a) calling a split(” “) method (space as delimiter) on this string will convert it to an array of four strings [1] – This [2] – is [3] – a [4] – String a) calling a split(” “, 2) method on this string will convert it to an array of 2 strings [1] – This [2] – is a String

2. Simplest thing first – Using the split() method with one character delimiter

As you can see the split method supports regular expression, therefore, we should be able to use one or more characters as a delimiter. To start with the simple example I have chosen comma “,” as a delimiter for my sentence. So for example, if you have a string [“This, is, a, String”] then a split using comma as delimiter should result in the array of four strings. See below example code.

public static void  singleCharacterDelimiterTest() {
String str = "This,is,a,String";
String delimiter = ",";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println(splitStrings[i]);
}
}

3. How about using another string as a delimiter?

Yes, you can always use a string as a delimiter. Remember that delimiter is a regular expression, therefore, any valid regular expression can be passed as a value in this parameter. So for example, if you have a string [“ThisWORDisWORDaWORDString”] then a split using the word [WORD] as a delimiter is going result in an array of four strings. See below example code.

public static void  singleWordDelimiterTest() {
String str = "ThisWORDisWORDaWORDString";
String delimiter = "WORD";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println(splitStrings[i]);
}
} 

The output of this method will be

[0] This
[1] is
[2] a
[3] String

4. How about using multiple characters as a delimiter?

There can be some scenarios where you may want to split the string based on multiple characters. So for example, if you have a string [“This, is: a; String”] then a split using [comma or colon or semi-colon] as a delimiter is required. You need not to be an expert in Regular Expression to do this, just a simple use of pipe (|) operator should be sufficient to deal with this. so the regular expression for these 3 delimiters will be [“,|:|;”] See below example code.

public static void  multiCharacterDelimiterTest() {
String str = "This,is:a;String";
String delimiter = ",|:|;";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println("[" + i + "] "+ splitStrings[i]);
}
}

The output of this method will be

[0] This
[1] is
[2] a
[3] String

5. How about using multiple words as a delimiter?

Let’s assume a hypothetical scenario where you may want to split the string based on multiple words. So for example, if you have a string [“ThisWORD1isWORD2aWORD3String”] then a split using [WORD1 or WORD2 or WORD3] as a delimiter is required. Again the use of pipe (|) operator should be sufficient to deal with this. so the regular expression for these 3 delimiters will be [“WORD1|WORD2|WORD3”] See below example code.

public static void  multiWordDelimiterTest() {
String str = "ThisWORD1isWORD2aWORD3String";
String delimiter = "WORD1|WORD2|WORD3";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println("[" + i + "] "+ splitStrings[i]);
}
}

The output of this method will be

[0] This
[1] is
[2] a
[3] String

6. Keeping a watch on a few special characters

As we discussed in previous scenarios, the delimiter field is a regular expression and therefore there are few characters which have special meanings. If any such character needs to use as a delimiter then an escape sequence of \ should be used in delimiter string. Some example characters are a pipe (|), dollar sign ($), dot (.) carat (^) See below example code.

public static void  specialCharaterDelimiterTest() {
String str = "This|is^a$String";
String delimiter = "\||\^|\$";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println("[" + i + "] "+ splitStrings[i]);
}
}

The output of this method will be

[0] This
[1] is
[2] a
[3] String

You can try many other regular expression and explore the power of this method. Visit http://www.regular-expressions.info/ to get a more in-depth understanding of regular expressions.

7. String Split using Java 1.1 Style – Using StringTokenizer class

StringTokenizer is a legacy class which is part of JDK since version 1.1. The String Tokenizer class allows an application to break a string into tokens. The set of delimiters (the characters that separate tokens) may be specified either at creation time or on a per-token basis. StringTokenizer’s nextToken() method can be used to produce the exact same output, See below example code.

public static void splitByTokenizer() {
StringTokenizer st = new StringTokenizer("This,is:a;String",",:;");
while (st.hasMoreTokens()) {
System.out.println(st.nextToken());
}
}

The output of this method will be

This
is
a
String

The split() method has been introduced since JDK version 1.4 and StringTokenizer use has been discouraged after that. Here is what Sun suggest in JDK 1.6 Javadocs “StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code. It is recommended that anyone seeking this functionality use the split method of String or the java.util.regex package instead.” Let me know your comments/feedback on this tutorial.