Java String .substring() method explained with examples

📚 Quick Study Guide: Java String .substring()

• 🎯 Purpose: The `substring()` method in Java is used to extract a portion of a string, creating a new string from a sequence of characters within the original.
• 🛠️ Two Overloaded Versions:
  • 📝 `substring(int beginIndex)`: Returns a new string that is a substring of this string. The substring begins with the character at the specified `beginIndex` and extends to the end of this string.
  • ✂️ `substring(int beginIndex, int endIndex)`: Returns a new string that is a substring of this string. The substring begins at the specified `beginIndex` and extends to the character at `endIndex - 1`. The character at `endIndex` is not included.
• 🔢 Zero-Based Indexing: Like arrays, Java strings use zero-based indexing. The first character is at index 0, the second at index 1, and so on.
• ✅ Inclusive `beginIndex`: The character at `beginIndex` is always included in the resulting substring.
• 🛑 Exclusive `endIndex`: The character at `endIndex` is always *excluded*. Think of `endIndex` as "up to, but not including."
• 📏 Length Calculation: The length of the substring created by `substring(beginIndex, endIndex)` is $endIndex - beginIndex$.
• ⚠️ `IndexOutOfBoundsException`: This exception is thrown if `beginIndex` is negative, greater than `length()`, or if `beginIndex` is greater than `endIndex`, or if `endIndex` is negative or greater than `length()`.
• 💡 Common Use Cases: Extracting parts of file names, parsing data, truncating strings.

🧠 Practice Quiz: Java String .substring()

1. Question 1:

   Given the string `String s = "Hello World";`, what will be the output of `s.substring(6);`?

   A) "World"

   B) " World"

   C) "o World"

   D) "Hello"

2. Question 2:

   Consider `String text = "JavaProgramming";`. What does `text.substring(4, 8);` return?

   A) "Progr"

   B) "Prog"

   C) "aPro"

   D) "aProgr"

3. Question 3:

   If `String data = "eokultv";`, what is the result of `data.substring(0, 3);`?

   A) "eok"

   B) "eoku"

   C) "okul"

   D) "e"
4. Question 4:

   Which of the following method calls would throw an `IndexOutOfBoundsException` for `String str = "Example";`?

   A) `str.substring(0, 7);`

   B) `str.substring(7);`

   C) `str.substring(2, 1);`

   D) `str.substring(3, 3);`

5. Question 5:

   What is the length of the string returned by ` "Programming".substring(3, 7);`?

   A) 3

   B) 4

   C) 7

   D) 10

6. Question 6:

   Given `String sentence = "Learning Java is fun";`, what does `sentence.substring(sentence.indexOf("Java"), sentence.indexOf(" is"));` produce?

   A) "Java is"

   B) "Java"

   C) "Java "

   D) "Java i"

7. Question 7:

   If `String val = "Developer";`, what is the output of `val.substring(val.length() - 3);`?

   A) "per"

   B) "oper"

   C) "eloper"

   D) "Dev"