Important: The character data type represents single characters.

Besides processing numeric values, Java can also process characters. The char data type is used to represent single characters. Character literals are enclosed in single quotes.

Example:

char letter = 'A';
char numChar = '4';

Important Distinction:

• ▶ String literals must be enclosed in double quotes (" ")
• ▶ Character literals are single characters enclosed in single quotes (' ')

Thus, "A" is a string, while 'A' is a character.

16-bit Unicode: Occupies two bytes, represented by four hexadecimal digits preceded by \u, from \u0000 to \uFFFF.

Examples: Greek letters α, β, γ are \u03b1, \u03b2, \u03b4 respectively.

Equivalent statements:

char letter = 'A';
char letter = '\u0041';  // Unicode for 'A' is 0041
// Both statements assign character 'A' to variable letter

Increment/Decrement with char: You can use increment and decrement operators with char variables.

char ch = 'a';
System.out.println(++ch);  // Displays 'b'

Example with quotes:

System.out.println("He said: \"Let's go!\"");
// Output: He said: "Let's go!"

Example with backslash:

System.out.println("\\t is a tab character");
// Output: \t is a tab character

Character comparison examples:

'a' < 'b'     // true (97 < 98)
'a' < 'A'     // false (97 > 65)
'1' < '8'     // true (49 < 56)

Example using Character methods:

char ch = 'A';

if (Character.isUpperCase(ch)) {
    System.out.println(ch + " is uppercase");
}
if (Character.isDigit(ch)) {
    System.out.println(ch + " is a digit");
}

char lowerCh = Character.toLowerCase(ch);  // 'a'

Important: A string is a sequence of characters. The String class is used to represent strings in Java.

String declaration:

String message = "Welcome";

Examples:

String message = "Welcome to Java";
int len = message.length();        // 15
char ch = message.charAt(0);       // 'W'
String upper = message.toUpperCase(); // "WELCOME TO JAVA"
String lower = message.toLowerCase(); // "welcome to java"
String trimmed = "  Hello  ".trim();    // "Hello"

String concatenation:

String s1 = "Hello";
String s2 = "World";
String s3 = s1.concat(s2);    // "HelloWorld"
String s4 = s1 + s2;           // "HelloWorld" (using + operator)
String s5 = s1 + " " + s2;     // "Hello World"

Reading strings using next():

Scanner input = new Scanner(System.in);
System.out.print("Enter three words: ");
String s1 = input.next();   // Reads until first whitespace
String s2 = input.next();
String s3 = input.next();

Reading entire line using nextLine():

System.out.print("Enter a line: ");
String line = input.nextLine();  // Reads entire line until Enter

Reading a character:

System.out.print("Enter a character: ");
String s = input.nextLine();
char ch = s.charAt(0);  // Get first character

Lab 1: Working with Strings

Objective: Create a program that prompts user to enter names of two cities and displays them in alphabetical order. Replace three dots (...) in the code with necessary code.

[File name and class name: L6Lab1.java]

Enter name of first city:
Voronezh
                        
Enter name of second city:
                        
Moscow
City names in alphabetical order: Moscow Voronezh
                        

                        

Algorithm:

1. Create a new Java file named L6Lab1.java.
2. Import the Scanner class for user input:

   
   import java.util.Scanner;

3. Define the class L6Lab1 with a main method.
4. Step 1: Get names of two cities from user. Use nextLine() method to read city names that may contain spaces:

   
   Scanner input = new Scanner(System.in);
   
   // Get names of two cities
   System.out.print("Enter name of first city: ");
   String city1 = ...;
   System.out.print("Enter name of second city: ");
   String city2 = ...;

5. Important: Using nextLine() instead of next() allows reading city names that may contain multiple words separated by spaces.
6. Step 2: Compare the two city names using compareTo() method and display them in alphabetical order:

   
   if (city1.compareTo(city2) < 0) {
       System.out.println("City names in alphabetical order: " + 
           city1 + " " + city2);
   } else {
       System.out.println("City names in alphabetical order: " + 
           ... + " " + ...);
   }

7. Important: The compareTo() method returns:
   • ▶ Negative value if city1 is less than city2 (comes earlier in alphabetical order)
   • ▶ Zero if city1 equals city2
   • ▶ Positive value if city1 is greater than city2 (comes later in alphabetical order)
8. Close the Scanner object.
9. Test the program with different city names (including multi-word names like "New York" or "St. Petersburg").
10. Add the task description as a comment at the beginning of the program.
11. Upload the file to the learning management system.

Task 1: Character Type Operations

Objective: Write a program to:

• ▶ Find and output ASCII codes corresponding to characters '1', 'A', 'B', 'a', and 'b'
• ▶ Find and output characters corresponding to decimal codes 40, 59, 79, 85, and 90
• ▶ Find and output characters corresponding to hexadecimal codes 40, 5A, 71, 72, and 7A

ASCII code for '1' = 49
ASCII code for 'A' = 65
ASCII code for 'B' = 66
ASCII code for 'a' = 97
ASCII code for 'b' = 98

Character for decimal 40 = (
Character for decimal 59 = ;
Character for decimal 79 = O
Character for decimal 85 = U
Character for decimal 90 = Z

Character for hex 40 = @
Character for hex 5A = Z
Character for hex 71 = q
Character for hex 72 = r
Character for hex 7A = z

Hint: Use type casting between char and int, and Unicode escape sequences for hexadecimal values.

[File name and class name: L6Task1.java]

Task 2: String Type Operations

Objective: Let s1 be " Welcome " and s2 be " welcome ". Write code for the following statements:

1. Check if s1 equals s2 and assign result to boolean variable isEqual
2. Compare s1 and s2 and assign result to int variable x
3. Check if s1 has prefix "AAA" and assign result to boolean variable b
4. Assign length of s1 to int variable x
5. Assign first character of s1 to char variable x
6. Create new string s3 by concatenating s1 and s2
7. Create substring of s1 from index 1 to index 4
8. Create new string s3 by converting s1 to lowercase
9. Create new string s3 by trimming whitespace from both ends of s1

isEqual = false
x = -32
b = false
Length x = 9
First char x = ' '
s3 = " Welcome welcome "
Substring = "Welc"
Lowercase s3 = " welcome "
Trimmed s3 = "Welcome"

Hint: Use string methods equals(), compareTo(), startsWith(), length(), charAt(), concat() or + operator, substring(), toLowerCase(), trim().

[File name and class name: L6Task2.java]

Task 3: Find Substring Between Characters

Objective: A character is entered (stored in variable c). There is a string s containing exactly two characters c. Find the substring between these two characters.

Result for "astra" string and 'a' char is: str
Result for "nana" string and 'a' char is: n

Hint: Use indexOf() method to find positions of the character, then substring() to extract text between them.

[File name and class name: L6Task3.java]

Task 4: Word Counter

Objective: Write a program that reads multiple words using next() and displays them in reverse order.

Enter 5 words: 
one
two
three
four
five

In reverse order:
five four three two one

Hint: Use .next() method.

[File name and class name: L6Task4.java]

Task 5: Name Formatter

Objective: Create a program that formats a full name.

Enter first name: Ivan 
Enter last name: Bikov

Result:
Full name: Ivan Bikov
Uppercase: IVAN BIKOV
Initials: I.B.
Last, First: Bikov, Ivan

Hint: Use toUpperCase() and charAt(0) methods.

[File name and class name: L6Task5.java]

Task 6: Find Substring Between Characters

Objective: A character is entered (stored in variable c). There is a string s containing exactly two characters c. Find the substring between these two characters.

Result for "astra" string and 'a' char is: str
Result for "nana" string and 'a' char is: n

Hint: Use indexOf() method to find positions of the character, then substring() to extract text between them.

[File name and class name: L6Task6.java]