Substrings are snippets of text extracted from a larger string. In Java, this is done for a variety of reasons, ranging from extracting particular characters or patterns from a string, to manipulating strings themselves in order to perform specific tasks. Knowing how to create a substring in Java can be very useful to developers, as it provides them with the ability to carry out specific operations on strings.

What is a Substring?

A substring is a portion of text or characters that have been taken from a larger string. Substrings are often used in programming in a variety of ways, such as: extracting specific parts of a string; manipulating strings; and performing specific operations on strings. It’s important to note that the substring itself is a part of the original string, and therefore shares characteristics with the original string (such as the length). It’s also important to note that the substring is not the same as the original string, as it only contains a portion of the original.

Substrings can be used to search for specific words or phrases within a larger string. For example, if you wanted to search for the word “cat” within a larger string, you could use a substring to search for it. Additionally, substrings can be used to compare two strings to see if they are the same or different. This can be useful for checking if two strings are an exact match or if they contain different characters.

The Basics of Substring in Java

The basic concept of a substring in Java is quite simple. To create a substring in Java, you first need to define the string from which the substring will be extracted. Usually this is done by either giving the string variable a value or assigning it to a variable. Once the string has been defined, you can choose the starting and ending points for your substring, which will determine which portion of text will be extracted from the test.

The starting point of the substring is determined by the index of the character in the string. The ending point is determined by the length of the substring. For example, if you wanted to extract the first five characters of a string, you would set the starting point to 0 and the ending point to 5. The substring would then be the first five characters of the string.

How to Create a Substring in Java

Once the string has been defined and the start and end points have been determined, creating a substring in Java is relatively simple. For example: if you have a string containing the labels ‘2012-01-29’ and you wanted to extract only the day (29), then you could use the Java ‘substring’ method to create a substring out of that string.

To create a substring in Java, you must first define the string you want to use. Then, you must determine the start and end points of the substring. Once these two steps have been completed, you can use the Java ‘substring’ method to create the substring. This method will return the substring that you have specified.

Using the String Class to Create a Substring

Java Strings are actually instances of the String class, which makes them objects. As such, they can be manipulated to perform specific tasks such as creating substrings. This is performed using the ‘substring’ method which takes two parameters, one for the beginning index and one for the ending index of the substring. In this example, it would be from index 0 (which is the beginning of the string) to index 4 (which is the fifth character in the string) which would give us the value ‘2012’.

The substring method can also be used to create a substring from the end of a string. To do this, you would use the length of the string as the second parameter. For example, if the string was ‘Hello World’, the substring method could be used to create a substring from index 6 to the end of the string, which would give us the value ‘World’.

Using the Substring Method

Once you have defined the beginning and ending index for your substring, you need to specify which type of substring method you want to use. The two options for creating substrings in Java are either the ‘substring’ method or the ‘subSequence’ method. The ‘substring’ method takes two parameters – one for the starting index and another for the ending index – while the ‘subSequence’ method takes two parameters – one for the starting index and another for the length – and both return a string object containing a substring of your larger string.

It is important to note that the substring method is case sensitive, meaning that the characters in the substring must match the characters in the original string exactly. Additionally, the substring method is immutable, meaning that any changes made to the substring will not affect the original string.

Examples of Creating a Substring in Java

Let’s look at some examples of how to create a substring using Java. Consider a string with this sequence: ‘text example’

• To create a substring from this sequence starting at index 3 to index 8, use: String subString = testString.substring(3, 8);

• To create a substring from this sequence starting at index 0 with a specific length of 4, use: String subSequence = testString.subSequence(0, 4);

It is also possible to create a substring from a sequence starting at the end of the string. To do this, use the length of the string as the second parameter in the substring method. For example, if the string is ‘text example’, the substring can be created using the following code: String subString = testString.substring(3, testString.length());

Extracting Particular Characters from Strings

Another way to use substrings in Java is to extract particular characters from strings. For example, if you wanted to extract all of the digits from a string of text, you could use a combination of regular expressions and substrings to do so. Let’s say we have a string that contains both letters and numbers: ‘text34example’

Using regular expressions we can identify all of the digits within this string by using this code: Pattern digitPattern = Pattern.compile("\\d");, and then using it in combination with substrings we can extract only those digits by using this code: Matcher match = digitPattern.matcher(testString); while (match.find()) { String digit = testString.substring(match.start(), match.end()); }

Manipulating Strings with Substrings

Substrings can also be used to manipulate strings in Java. For example, instead of just extracting parts of strings, you can also use substrings to replace parts of strings with new text. This can be useful if you need to make changes to large portions of text quickly and easily. To do this, you just need to specify which part of the string you want to replace and then provide the new text that you want to replace it with.

Conclusion

Creating substrings in Java is relatively straightforward and once you understand how it works it can be used for various operations on strings, including extracting particular characters or patterns from a string, manipulating strings, and performing specific tasks on strings. Knowing how to create a substring in Java can be very useful as they provide developers with much more control over strings and make working with them much easier.