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String Exercises

This directory contains exercises to help you practice working with String objects in Java using jshell.

Setup

  1. Open your terminal/command prompt
  2. Navigate to this directory
  3. Start jshell: jshell
  4. Load the exercise file: /open topic.jsh

Exercises

Exercise 1: String Basics

Write a method getStringLength(String text) that returns the length of a string (handle null strings). Write a method isStringEmpty(String text) that returns true if the string is null or empty.

Exercise 2: String Comparison

Write a method areStringsEqual(String str1, String str2) that safely compares two strings for equality (handle nulls). Write a method compareStringsIgnoreCase(String str1, String str2) that compares strings ignoring case differences.

Exercise 3: String Search and Contains

Write a method containsSubstring(String text, String search) that returns true if text contains the search string. Write a method findFirstPosition(String text, String search) that returns the index of the first occurrence of search in text (-1 if not found).

Exercise 4: String Extraction

Write a method getFirstCharacter(String text) that returns the first character of a string (handle empty strings). Write a method getLastCharacter(String text) that returns the last character of a string. Write a method getSubstring(String text, int start, int end) that returns a substring from start to end index.

Exercise 5: String Modification

Write a method makeUpperCase(String text) that converts a string to uppercase (handle null). Write a method makeLowerCase(String text) that converts a string to lowercase (handle null). Write a method trimWhitespace(String text) that removes leading and trailing spaces.

Exercise 6: String Building and Joining

Write a method concatenateStrings(String str1, String str2) that joins two strings together (handle nulls). Write a method repeatString(String text, int count) that repeats a string the specified number of times. Write a method joinWithSeparator(String[] words, String separator) that joins an array of strings with a separator.

Exercise 7: String Validation and Analysis

Write a method isValidEmail(String email) that returns true if email contains "@" and "." characters. Write a method countVowels(String text) that counts the number of vowels (a, e, i, o, u) in a string. Write a method isPalindrome(String text) that returns true if the string reads the same forwards and backwards.

Testing Your Code

After completing each exercise, test your methods with different inputs:

// Example tests
getStringLength("Hello")                    // Should return 5
isStringEmpty("")                          // Should return true
areStringsEqual("Hello", "hello")          // Should return false
compareStringsIgnoreCase("Hello", "HELLO") // Should return true
containsSubstring("Hello World", "World")  // Should return true
getFirstCharacter("Java")                  // Should return 'J'
makeUpperCase("hello")                     // Should return "HELLO"
concatenateStrings("Hello", " World")      // Should return "Hello World"
countVowels("Hello")                       // Should return 2
isPalindrome("racecar")                    // Should return true

Tips

  • Read the NOTES.md file first to understand String objects
  • Remember that Strings are immutable (cannot be changed)
  • Always handle null strings to avoid NullPointerException
  • Use .equals() to compare strings, not ==
  • String indices start at 0
  • Be careful with substring bounds to avoid StringIndexOutOfBoundsException