Java String subSequence() method
Syntax and Examples

Introduction

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.

Syntax

public CharSequence subSequence(int beginIndex,
             int endIndex)

Parameters

Parameter	Description
beginIndex	The index (inclusive) of the first character in the subsequence.
endIndex	The index (exclusive) of the last character in the subsequence.

Return Value

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

Examples

Example 1: Basic Subsequence Extraction

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.

Example 2: Extracting from the Middle

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.

Example 3: Extracting the Last Few Characters

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.

Example 4: Handling Edge Cases - Beginning to End

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.

Important Considerations

• 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.