Java String substring() method
Syntax and Examples

Syntax

public String substring(int beginIndex) 

public String substring(int beginIndex,
                         int endIndex)

Parameters

Parameter	Description
beginIndex	The index at which the substring begins (inclusive).
endIndex	The index at which the substring ends (exclusive). That is, the character at endIndex is not included in the substring.

Return Value

The substring() method returns a new String that is a substring of the original string.

Examples

Example 1: Extracting from a single index

This example demonstrates using substring() with only the starting index. It extracts characters from the beginning of the string up to (but not including) the specified index.

String str = "Hello World";
String sub = str.substring(5); // Extract substring starting at index 5
System.out.println(sub);

World

Here, we start the substring from index 5 of "Hello World". Index 5 points to the character 'W'. The returned substring includes characters at indices 5, 6, 7, 8, 9, and 10 ('W', 'o', 'r', 'l', 'd').

Example 2: Extracting between two indexes

This example shows how to specify both a starting and ending index for the substring.

String str = "Hello World";
String sub = str.substring(0, 5); // Extract substring from index 0 up to (but not including) index 5
System.out.println(sub);

Hello

In this case, we're extracting a substring that starts at index 0 and ends just before index 5. This includes the characters at indices 0, 1, 2, 3, and 4 ('H', 'e', 'l', 'l', 'o'). The character at index 5 (' ') is *not* included.

Example 3: Handling Index Out of Bounds

It's important to be aware that if your indices are out of bounds, you will get a StringIndexOutOfBoundsException. Let’s look at an example where we try to extract from an invalid index.

String str = "Hello";
// This line will throw StringIndexOutOfBoundsException because endIndex is out of bounds
//String sub = str.substring(0, 10); 
//System.out.println(sub);

The above code would result in a runtime error. When using the two-argument version of substring(), ensure that both beginIndex is non-negative and less than the length of the string, and that endIndex is greater or equal to beginIndex and less than the length of the string.

Example 4: Substring with start index equals string length

What happens when we specify a begin index equal to the string's length?

String str = "Hello";
String sub = str.substring(5); //beginIndex is equal to string length
System.out.println(sub);

When the begin index equals the string's length, an empty string is returned.

Example 5: Substring with start and end indexes equal

Let’s see what happens when we set both indexes to be equal in value

String str = "Hello";
String sub = str.substring(2, 2); //start index equals end index 
System.out.println(sub);

When the start and end indexes are equal an empty string is returned.