String subSequence() method - Syntax and Examples

Learn about the Java String subSequence() method. This tutorial covers syntax, parameters, return values, and provides practical examples.

This reference explains String subSequence() method - Syntax and Examples through its syntax, examples and boundaries. Use the linked course lessons when the surrounding Java concepts are unfamiliar.

The subSequence() method in Java's String class is a handy tool for extracting a portion of a string without actually creating any new copies of the original characters. Think of it as slicing a string, but instead of getting a new String object, you get a CharSequence.

public CharSequence subSequence(int beginIndex,
             int endIndex)

This method returns a CharSequence object representing the specified portion of the original string.

Let's start with a simple example to illustrate how the subSequence() method works. We'll extract a substring from an existing string, specifying the start and end indices.

String str = "Hello World";
CharSequence sub = str.subSequence(0, 5);
System.out.println(sub); // Output: Hello

Hello

In this example, we extract the characters from index 0 (inclusive) up to index 5 (exclusive). This results in the subsequence "Hello". Notice that it returns a CharSequence which is implemented by String. So you can use it like a string.

Here's an example demonstrating how to extract characters from the middle of a string.

String str = "Java Programming";
CharSequence sub = str.subSequence(5, 13);
System.out.println(sub); // Output: Program

Program

We're extracting characters from index 5 up to (but not including) index 13, giving us "Program". This highlights that the `endIndex` is exclusive.

This example shows how to extract the last few characters of a string using subSequence(). This can be useful for things like extracting file extensions or processing the end of log messages.

String str = "example.txt";
CharSequence sub = str.subSequence(8, str.length());
System.out.println(sub); // Output: txt

txt

We're extracting from index 8 until the end of the string (using `str.length()`). This gives us "txt", which is the file extension in this case.

What happens when you want a copy of the entire string? This example demonstrates that scenario

String str = "Entire String";
CharSequence sub = str.subSequence(0, str.length());
System.out.println(sub); // Output: Entire String

Entire String

Extracting the entire string will return a CharSequence containing all of it.

• IndexOutOfBoundsException: If either beginIndex or endIndex are out of bounds (negative, or greater than the length of the string), an IndexOutOfBoundsException will be thrown.
• CharSequence vs. String: The method returns a CharSequence object, which is an interface that can be implemented by various classes, including String. You can generally treat it as if it were a String for most operations.

Check the example’s types, inputs and documented behavior before copying it into an application. Some APIs require external libraries, files or platform services; consult their setup notes.

Related explanations: Java Data Types - Primitive and Non-Primitive, Java Class - Blueprint of Objects, Exceptions in Java Introduction.

Supporting documentation: Official Java learning guide.