Substring in Java

A part of String is called substring. In other words, substring is a subset of another String. Java String class provides the built-in substring() method that extract a substring from the given string by using the index values passed as an argument. In case of substring() method startIndex is inclusive and endIndex is exclusive.

Suppose the string is "computer", then the substring will be com, compu, ter, etc.

Note: Index starts from 0.

You can get substring from the given String object by one of the two methods:

1. public String substring(int startIndex):
   This method returns new String object containing the substring of the given string from specified startIndex (inclusive). The method throws an IndexOutOfBoundException when the startIndex is larger than the length of String or less than zero.
2. public String substring(int startIndex, int endIndex):
   This method returns new String object containing the substring of the given string from specified startIndex to endIndex. The method throws an IndexOutOfBoundException when the startIndex is less than zero or startIndex is greater than endIndex or endIndex is greater than length of String.

In case of String:

• startIndex: inclusive
• endIndex: exclusive

Let's understand the startIndex and endIndex by the code given below.

In the above substring, 0 points the first letter and 2 points the second letter i.e., e (because end index is exclusive).

Example of Java substring() method

TestSubstring.java

Output:

Original String: SachinTendulkar
Substring starting from index 6: Tendulkar
Substring starting from index 0 to 6: Sachin

The above Java programs, demonstrates variants of the substring() method of String class. The startindex is inclusive and endindex is exclusive.

Using String.split() method:

The split() method of String class can be used to extract a substring from a sentence. It accepts arguments in the form of a regular expression.

TestSubstring2.java

Output:

[Hello,  My name is Sachin]

In the above program, we have used the split() method. It accepts an argument \\. that checks a in the sentence and splits the string into another string. It is stored in an array of String objects sentences.