String.substring()

// Extracts from the start index to the end of the string.
str.substring(int beginIndex);

// Extracts from the start index up to (but not including) the end index.
str.substring(int beginIndex, int endIndex);

// Extracts from the start index to the end of the string.
String str = "Hello, Java!";
System.out.println(str.substring(7)); // Prints "Java!"

// Extracts a range by specifying start and end indexes.
System.out.println(str.substring(0, 5)); // Prints "Hello"

// Extracts the year, month, and day from a date string.
String date = "2025-06-15";
String year  = date.substring(0, 4); // "2025"
String month = date.substring(5, 7); // "06"
String day   = date.substring(8);    // "15"
System.out.println(year + "/" + month + "/" + day);
// Prints "2025/06/15"

// Combines with indexOf() to extract dynamically.
String email = "user@example.com";
int atIndex = email.indexOf("@");
String domain = email.substring(atIndex + 1); // "example.com"
System.out.println(domain);

// Extracts the last 3 characters.
String filename = "report.pdf";
String ext = filename.substring(filename.length() - 3); // "pdf"
System.out.println(ext);

substring() extracts a portion of a string and returns it as a new string. Indexes are zero-based, and the character at the end index is not included in the result. For example, substring(0, 5) returns characters at positions 0 through 4.

If the index is negative, beginIndex is greater than endIndex, or the index exceeds the length of the string, a StringIndexOutOfBoundsException is thrown. Use length() to check the string length beforehand to avoid this.

To get the length of a string, see length() / charAt(). To combine substring extraction with searching, see indexOf() / contains().