About this video

• Video Title: Lecture 57 : Applications of String
• Channel: NPTEL IIT Kharagpur
• Speakers: None
• Duration: 00:26:55

Overview

This video lecture focuses on the practical applications and methods for manipulating strings in programming. It covers string comparison, substring extraction, searching within strings, and data conversion between strings and various primitive data types.

Key takeaways

• String Comparison: Various methods exist to compare strings, including case-sensitive and case-insensitive comparisons, and the compareTo method which orders strings lexicographically based on Unicode values.
• Substring Operations: Methods like substring, replace, split, and startsWith allow for extracting parts of strings, modifying them, and checking for specific prefixes.
• String Searching: Functions like indexOf and lastIndexOf help find the first or last occurrence of a substring within a larger string, returning the index.
• Data Conversion: Strings can be converted to primitive data types (like int, float, double) using wrapper classes and their parse methods. Conversely, primitive data types and objects can be converted to their string representations using methods like toString or String.valueOf().
• Command-line Arguments: String parsing is crucial when dealing with command-line arguments, as inputs must be converted to the appropriate data types, and type mismatches can lead to exceptions.

Here are some Multiple Choice Questions (MCQs) based on the video transcript, suitable for an exam:

1. Which method is used to compare two strings for equality, ignoring their case differences? a) equals() b) compareTo() c) equalsIgnoreCase() d) compareToIgnoreCase()

   Answer: c) equalsIgnoreCase()

2. The compareTo() method in string comparison returns: a) true if the strings are equal, false otherwise. b) A positive value if the first string is lexicographically greater than the second, a negative value if it's less, and zero if they are equal. c) The index of the first occurrence of the substring. d) A new string with specified characters replaced.

   Answer: b) A positive value if the first string is lexicographically greater than the second, a negative value if it's less, and zero if they are equal.

3. The substring(int beginIndex) method in Java returns: a) A new string that is a substring of the original string, from beginIndex to the end of the string. b) A new string that is a substring of the original string, from beginIndex up to, but not including, endIndex. c) The index of the first occurrence of the specified substring. d) The original string if the substring is found, otherwise an empty string.

   Answer: a) A new string that is a substring of the original string, from beginIndex to the end of the string.

4. To convert a string representing an integer (e.g., "123") into an actual integer data type, which method is typically used? a) Float.parseFloat() b) Integer.toString() c) Integer.parseInt() d) String.valueOf()

   Answer: c) Integer.parseInt()

5. When converting different data types (like integers, floats, booleans) into their string representation, which method is commonly used and defined in the Object class? a) toString() b) valueOf() c) convertToString() d) getString()

   Answer: a) toString()

6. If a command-line argument passed to a program is "hello" and the program attempts to parse it as an integer using Integer.parseInt(), what will happen? a) It will return 0. b) It will return -1. c) It will throw a NumberFormatException (or IOException as mentioned in the context of type mismatch). d) It will return the string "hello" as an integer.

   Answer: c) It will throw a NumberFormatException (or IOException as mentioned in the context of type mismatch).

7. The String.valueOf() method is a versatile way to: a) Compare two strings only. b) Extract a portion of a string. c) Convert various data types (primitives, objects) into their string representation. d) Search for a substring within a string.

   Answer: c) Convert various data types (primitives, objects) into their string representation.

8. What is the primary purpose of the indexOf() method when used with a string argument? a) To find the last occurrence of the substring. b) To check if the string starts with the given substring. c) To return the index of the first occurrence of the specified substring within the string. d) To replace all occurrences of the substring with another string.

   Answer: c) To return the index of the first occurrence of the specified substring within the string.

9. The compareToIgnoreCase() method compares two strings: a) Lexicographically, considering the case of characters. b) Lexicographically, ignoring the case of characters. c) Only for equality, ignoring case. d) Based on their length.

   Answer: b) Lexicographically, ignoring the case of characters.

10. When a variable of a custom class type (e.g., a Student object) is passed to System.out.println(), what method is implicitly called to get its string representation? a) String.valueOf(variable) b) variable.toString() c) Both a) and b) can be involved, depending on the implementation. d) variable.print()

    Answer: c) Both a) and b) can be involved, depending on the implementation. (The println method internally uses String.valueOf() which in turn calls toString() on objects.)