In Java, you can convert a String to an int using several methods. Below are the most common approaches:

1. Using Integer.parseInt()

The Integer.parseInt() method is the most straightforward way to convert a String to an int.

Example:

1String numberStr = "123";
2int number = Integer.parseInt(numberStr);
3
4System.out.println(number); // Output: 123

Handling Exceptions:

If the input string is not a valid integer, it throws a NumberFormatException.

1try {
2    String invalidStr = "abc";
3    int number = Integer.parseInt(invalidStr);
4} catch (NumberFormatException e) {
5    System.out.println("Invalid integer format");
6}

2. Using Integer.valueOf()

The Integer.valueOf() method also converts a String to an int, but it returns an Integer object (not a primitive int).

Example:

1String numberStr = "456";
2int number = Integer.valueOf(numberStr);
3
4System.out.println(number); // Output: 456

• Auto-unboxing happens when assigning an Integer object to a primitive int.

3. Using Integer.decode()

Integer.decode() can parse numbers from a String, including those with prefixes like "0x" (hexadecimal), "0" (octal), or plain decimal numbers.

Example:

1String numberStr1 = "123";
2String numberStr2 = "0x7B"; // Hexadecimal
3String numberStr3 = "0173"; // Octal
4
5int decimal = Integer.decode(numberStr1);
6int hex = Integer.decode(numberStr2);
7int octal = Integer.decode(numberStr3);
8
9System.out.println(decimal); // Output: 123
10System.out.println(hex);     // Output: 123
11System.out.println(octal);   // Output: 123

4. Using parseInt() with a Radix

If the string represents a number in a specific base (radix), you can use Integer.parseInt() with a second argument for the radix.

Example:

1String binaryStr = "1010"; // Binary
2String hexStr = "7B";      // Hexadecimal
3
4int binary = Integer.parseInt(binaryStr, 2); // Base 2
5int hex = Integer.parseInt(hexStr, 16);      // Base 16
6
7System.out.println(binary); // Output: 10
8System.out.println(hex);    // Output: 123

5. Using Scanner Class

You can use the Scanner class to read and parse integers from strings.

Example:

1import java.util.Scanner;
2
3String numberStr = "789";
4Scanner scanner = new Scanner(numberStr);
5int number = scanner.nextInt();
6
7System.out.println(number); // Output: 789

Summary Table

Notes:

• Always handle NumberFormatException when converting strings to integers to ensure the input is valid.
• Use Integer.parseInt() for most cases where you need a primitive int.

By choosing the appropriate method, you can safely and effectively convert a String to an integer in Java. 🚀