Common wrapper methods in Java - Mini Project: Build & Apply

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Common wrapper methods

📖 Scenario: You are working on a simple Java program that processes numbers and text. You will use wrapper class methods to convert between strings and numbers, and to check character types.

🎯 Goal: Build a Java program that uses common wrapper methods to convert strings to numbers, numbers to strings, and check if a character is a digit or letter.

📋 What You'll Learn

Create a String variable with a numeric value

Create an int variable to hold the converted number

Use Integer.parseInt() to convert the String to int

Use Integer.toString() to convert the int back to String

Use Character.isDigit() and Character.isLetter() to check characters

💡 Why This Matters

🌍 Real World

Converting between strings and numbers is common when reading user input or processing text data.

💼 Career

Understanding wrapper methods helps in data validation, parsing, and formatting in many Java applications.

1

Create a String with a numeric value

Create a String variable called numberString and set it to the value "12345".

Java

// Your code here

💡 Need a hint?

Use double quotes to create a String in Java.

2

Convert the String to an int

Add a line to convert numberString to an int called number using Integer.parseInt(numberString).

Java

public class Main {
    public static void main(String[] args) {
        String numberString = "12345";
        // Your code here
    }
}

💡 Need a hint?

Use Integer.parseInt() to convert a numeric String to an int.

3

Convert the int back to a String

Add a line to convert the int number back to a String called convertedString using Integer.toString(number).

Java

public class Main {
    public static void main(String[] args) {
        String numberString = "12345";
        int number = Integer.parseInt(numberString);
        // Your code here
    }
}

💡 Need a hint?

Use Integer.toString() to convert an int to a String.

4

Check if characters are digits or letters

Add code to check if the character '5' is a digit using Character.isDigit('5') and if the character 'a' is a letter using Character.isLetter('a'). Print the results exactly as shown below.

Java

public class Main {
    public static void main(String[] args) {
        String numberString = "12345";
        int number = Integer.parseInt(numberString);
        String convertedString = Integer.toString(number);
        // Your code here
    }
}

💡 Need a hint?

Use System.out.println() to print the results.