How To Convert String To Int In Java

A robust programming language like Java is frequently employed to build applications and software in various industries, including banking, healthcare, and education. Transforming a string to an integer is an uncommon task when performing data manipulation in java programming.

In Java, there are multiple ways to convert a string to an integer like Integer.parseInt() method, Integer.valueOf() method, Integer.decode() method, Scanner.nextInt() method, Type Casting.

Each method has its own advantages and disadvantages at which we will be taking a close look in this blog which will also include some sample problems.

Need to convert a string to int in java?

It is frequently necessary to transform a string into an integer in Java programmes. Among the most typical situations are:

1. User Input: When a user must enter a number into an application, the input is frequently in string format. The input must be transformed into an integer before any computations or comparisons with it can be done.

2. File Input/Output: When reading from or writing to a file, the data is usually in string format. If the data contains numerical values, they must be converted to integers in order to be manipulated properly.

3. Database Input/Output: When retrieving or storing data in a database, the data is typically in string format. If the data contains numerical values, they must be converted to integers before they can be used.

4. Mathematical Calculations: When performing mathematical calculations, the operands must be of the same data type. If one operand is a string and the other is an integer, the string must be converted to an integer before the calculation can be performed.

In short, converting a string to an integer is necessary to perform mathematical operations, to compare values, or to use the values in data storage or retrieval.

Different Methods for converting string to int

There are several methods which answers the question: How top convert a string to an integer in java and following are some of those methods:

1. Integer.parseInt() method
2. Integer.valueOf() method
3. Integer.decode() method
4. Scanner.nextInt() method
5. Type Casting

Detailed Explanation:

1. Integer.parseInt() method to change string to int:

Java includes a built-in method called parseInt() that may be used to parse a string and return an integer value. It returns an integer value after accepting a string as an input parameter. Invalid integer strings will result in a NumberFormatException being thrown by this procedure.

Sample code:

String str = “123”; int num = Integer.parseInt(str); System.out.println(num);

Output:

123

Explanation:

1. Str variable  = “123”.
2. The parseInt() method is called on the Integer class, with the str variable as an argument.
3. The result of the parseInt() method is assigned to the num variable.
4. The num variable is then printed to the console using the System.out.println() method.

2. Integer.valueOf() method to change string into int:

Another built-in Java technique for parsing strings and returning integer values is the function valueOf() { [native code] }() function. This function returns an Integer object and accepts a string as an input parameter. A NumberFormatException is also thrown by this procedure if the string is not an integer.

Sample code:

String str = "123";
Integer num = Integer.valueOf(str);
System.out.println(num);

Output:

123

Explanation:

1. The str variable is a string containing the value “123”.
2. The valueOf() method is called on the Integer class, with the str variable as an argument.
3. The result of the valueOf() method is assigned to the num variable.
4. The num variable is then printed to the console using the System.out.println() method.

3. Convert string to int in java with Integer.decode() method:

The decode() method is also a built-in method in Java which is used to decode a string into an integer. This method takes a string as an input parameter and returns an integer value. The string can start with either 0x or 0X for hexadecimal values or with 0 for octal values.

Sample code:

String str = "123";
int num = Integer.decode(str);
System.out.println(num);

Output:

123

Explanation:

1. A string with the value “123” makes up the str variable.
2. In the Integer class, the decode() function is invoked with the str argument.
3. The num variable is given the outcome of the decode() method.
4. Following that, the System.out.println() function prints the num variable to the console.

4. Scanner.nextInt() method to convert string into int:

The Scanner class can be used to read the input entered by the user. Integers can be read from the console using nextInt() method. This method returns an integer value without any input parameter and this method only converts strings to an integer those who are already written as an integer.

Sample code:

Scanner sc = new Scanner(System.in);
System.out.println("Enter a number: ");
int num = sc.nextInt();
System.out.println(num);

Output:

Enter a number:
123
123

Explanation:

1. An instance of the Scanner class is created with the System.in parameter, which represents the standard input stream.
2. The nextInt() method is called on the Scanner object, which reads an integer from the console.
3. The result of the nextInt() method is assigned to the num variable.
4. The num variable is then printed to the console using the System.out.println() method.

5. Type Casting for string to int in java:

In Java, type casting is another method for converting a string to an integer. With this technique, a string is transformed into a char array, and then the parseChar() method is used to turn each character into an integer. This approach is not advised because it is trickier and more prone to mistakes than the other approaches discussed above.

Sample code:

String str = "123";
int num = Integer.parseInt(str);
num = (int)num;
System.out.println(num);

Output:

123

Explanation:

1. The str variable containing the value “123”.
2. The parseInt() method is called on the Integer class
3. The result stored inside num variable.
4. The num variable is then type casted to an int.
5. The num variable is then printed to the console using the System.out.println() method.

Best out of Five Methods?

The Integer.parseInt() method is regarded as the best technique for converting a string into an integer in Java for a number of reasons.

1. Built-in Functionality: The Java language includes a built-in function called Integer.parseInt(). This indicates that it is already included in the Java library and does not call for the creation of any new dependencies or pieces of code.

• Handling exceptions: If the string is not an integer, the parseInt() method throws a NumberFormatException. This enables programmers to handle exceptions and stop a programme from crashing as a result of bad input.

• Flexibility: Unlike other conversion techniques, the parseInt() method may handle strings that have leading or trailing whitespace characters.

• Performance: The parseInt() method is generally faster and more efficient than other methods because it uses primitive types instead of objects.

• Versatility: The parseInt() method can handle a wide range of integer values, including negative numbers, decimal numbers, and hexadecimal values.

• Ease of Use: The parseInt() method takes only one argument, which is the string to be converted. This makes it easy to use and understand, even for beginner programmers.

Overall, the Integer.parseInt() method is the preferred method for converting a string into an integer in Java because of its built-in functionality, exception handling, flexibility, performance, versatility, and ease of use.

Sample Problems:

Problem 1: Write a program that prompts the user to enter their age as a string and then converts it to an integer. The program should then calculate and output the user’s birth year by subtracting their age from the current year. note convert string to integer using parseInt() method.

Code:

import java.util.Calendar;
import java.util.Scanner;

public class AgeToYear {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Prompt user for their age
        System.out.print("Enter your age: ");
        String ageStr = scanner.nextLine();

        // Convert age from string to integer using parseInt() method
        int age = Integer.parseInt(ageStr);

        // Get the current year from the system calendar
        int currentYear = Calendar.getInstance().get(Calendar.YEAR);

        // Calculate birth year by subtracting age from current year
        int birthYear = currentYear - age;

        // Output birth year to the console
        System.out.println("Your birth year is: " + birthYear);
    }
}

Output:

Enter your age: 25
Your birth year is: 1998

Explanation:

1. The necessary classes, java.util.Calendar and java.util.Scanner, imported.
2. In order to read user input from the console, create a Scanner object.
3. Ask the user to provide their age by using the system.
4. using Scanner.nextLine to read the data and out.print() ().
5. To convert the age string to an integer, use Integer.parseInt().
6. Put Calendar.getInstance to use ().
7. To acquire the current year from the system calendar, use get(Calendar.YEAR).
8. Subtract the age from the current year to determine the birth year.
9. the birth year using System.out.println and writing it to the console ().

Problem 2: Write a program that reads in a string of digits representing a binary number and converts it to its decimal equivalent. The program should output the decimal equivalent as an integer. note convert string to integer using valueof() method.

Code:

import java.util.Scanner;

public class BinaryToDecimal {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        
        //Prompt user
        System.out.print("Enter a binary number: ");
        String binary = input.nextLine();
        
       // conversion of string to int
        int decimal = Integer.valueOf(binary, 2);
        
        System.out.println("Decimal equivalent: " + decimal);
    }
}

Output:

Enter a binary number: 1010
Decimal equivalent: 10

Explanation of the code:

1. We import the Scanner class to get user input.
2. We prompt the user to enter a binary number as a string and read it in using Scanner.nextLine() method and store it in the variable binary.
3. We convert the binary string to decimal using the Integer.valueOf() method. The first argument to the method is the binary string, and the second argument is the base (2 for binary). The method returns the decimal equivalent as an integer, which we store in the variable decimal.
4. We output the decimal equivalent using System.out.println() method.

Problem 3:  Write a program that reads in a string of integers separated by spaces and finds the sum of the integers. The program should convert each string to an integer before adding it to the sum.  note convert string to integer using decode() method.

Code:

import java.util.Scanner;

public class SumOfIntegers {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Read in a string of integers separated by spaces
        System.out.print("Enter integers separated by spaces: ");
        String input = scanner.nextLine();

        // Split the string into individual numbers and sum them up
        int sum = 0;
        String[] numbers = input.split(" ");
        for (String number : numbers) {
            sum += Integer.decode(number);
        }

        // Output the sum of the integers
        System.out.println("The sum of the integers is: " + sum);
    }
}

Output:

Enter integers separated by spaces: 10 20 30 40
The sum of the integers is: 100

Explanation of the code:

1. Import the Scanner class from the java.util package.
2. Create a class called SumOfIntegers.
3. Create a main() method inside the SumOfIntegers class.
4. Create a new Scanner object called scanner to read input from the console.
5. Prompt the user to enter integers separated by spaces.
6. Read in the user’s input as a string using the nextLine() method of the scanner object.
7. Initialize a variable called sum to 0 to hold the total sum of the integers.
8. Split the input string into individual numbers using the split() method with a space as the delimiter.
9. Loop through each number in the numbers array using a for-each loop.
10. Convert each number from a string to an integer using the decode() method of the Integer class, and add it to the sum variable.
11. Output the sum of the integers to the console using the println() method.

Problem 4: Write a program that reads in a string of integers separated by commas and finds the median of the integers. The program should convert each string to an integer before finding the median. note convert string to integer using Type casting method.

Code:

import java.util.Arrays;

public class MedianCalculator {
    public static void main(String[] args) {
        // Read in string of integers separated by commas
        String input = "12,45,23,78,90,55,32";
        
        // Split the string by commas and store as string array
        String[] nums = input.split(",");
        
        int[] intArr = new int[nums.length];
        
        // Convert each string to integer and store in integer array
        for (int i = 0; i < nums.length; i++) {
            intArr[i] = Integer.parseInt(nums[i].trim());
        }
        
        // Sort the integer array
        Arrays.sort(intArr);
        
        // Find the median of the integers
        int median;
        if (intArr.length % 2 == 0) {
            median = (intArr[intArr.length / 2] + intArr[intArr.length / 2 - 1]) / 2;
        } else {
            median = intArr[intArr.length / 2];
        }
        
        System.out.println("Median of integers: " + median);
    }
}

Output:

Median of integers: 45

Explanation of code:

1. We start by defining the class MedianCalculator and the main method within it.
2. We initialize the input string with a sample input of integers separated by commas.
3. We split the input string by commas and store the resulting string array in nums.
4. We create an integer array intArr of the same size as nums.
5. We loop through each element of nums and convert it to an integer using Integer.parseInt() method and store it in intArr.
6. We sort the intArr using Arrays.sort() method.
7. We find the median of the integers using the formula for odd and even length arrays.
8. Finally, we output the median using System.out.println() method.

Conclusion:

In conclusion, converting a string to an integer is a common operation in Java programming. In this blog, we have discussed several methods for converting a string to an integer, including Integer.parseInt(), Integer.valueOf(), Integer.decode(), Scanner.nextInt() and Type Casting.

While all of these methods have their own advantages and disadvantages, Integer.parseInt() stands out as the most commonly used and efficient method due to its simplicity, speed and ability to handle invalid input.

It is always important to carefully choose the method that best suits your specific use case to ensure proper functionality and avoid errors in your Java code.