The process of converting a string into a long data type in Java refers to the transformation of the value of a string data type into a long data type. The size of the data does not affect this process. This conversion is performed because some operations can only be performed on a long data type instead of a string data type.
In Java, there are several methods for converting a string into a long data type, such as Long.parseLong(String), Long.valueOf(String), Decimal Format class, and Long Constructor.
Why is there a need to convert string to long in java?
There are several reasons why you might need to convert a string to a long in Java:
1. Data input: When data is read from an external source, such as a file or a user input, it is often stored as a string. To perform mathematical operations or to compare the data with other numerical values, it needs to be converted to a numerical data type, such as a long.
2. String concatenation: In Java, when you concatenate a string with a long using the + operator, the long is automatically converted to a string. This can result in loss of precision or unexpected results if the long value is large. Converting the long to a string first can prevent these issues.
3. Storing numerical data: In some cases, it might be more convenient to store numerical data as a string, such as when working with data that needs to be displayed to the user. In such cases, the data needs to be converted to a long when it is used in mathematical operations or comparisons.
4. Algorithmic processing: In certain algorithms, you might need to compare strings that represent numbers, such as when sorting a list of strings that represent numerical values. Converting these strings to longs can simplify the comparison process and make the algorithm more efficient.
Four Methods for converting string to long in Java:
There are several ways to convert a string to a long in Java:
- Long.parseLong(String s) method
- Long.valueOf(String s) method
- Using Long Constructor
- Using Decimal Format class
A thorough explanation of each strategy:
1. Long.parseLong(String s) method to convert string to long:
This is the most straightforward method to convert a string to a long. It returns the long representation of the string argument as a decimal number.
Sample code:
public class LongparseLong {
public static void main(String[] args) {
String txt = "55555";
try {
// conversion from string to long
long ext = Long.parseLong(txt);
System.out.println("The converted long value is: " + ext);
} catch (NumberFormatException e) {
// Not valid string throw exception
System.out.printf("Not valid string");
}
}}
Output:
The converted long value is: 555555Explanation:
- A Java class named Long.parseLong is declared with a main method.
- A string txt with the value “55555” is declared and initialised.
- A try-catch block is used to handle a possible NumberFormatException.
- Inside the try block, the Long.parseLong method is used to convert the string txt into a long value.
- The converted long value is then displayed on the screen using the System.out.println method.
- If the string txt is not a valid representation of a long, a NumberFormatException will be thrown, and the catch block will display an error message “Not valid string” on the screen.
2. Long.valueOf(String s) method to change string long in java:
This method returns a Long object that represents the string argument as a decimal number. You can then get the long value of the object using the longValue() method.
Sample Code:
import java.util.Scanner;
public class StringToLong {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter a string for long conversion: ");
String input = sc.nextLine();
sc.close();
try {
// Convert the input string to a long value using the valueOf method
long MathNumber = Long.valueOf(input);
System.out.print("The changed string: " + MathNumber);
} catch (NumberFormatException e) {
System.out.printf(" Not a valid string.");
}
}
}
Output:
Enter a string representation of a long value:
123456
The converted long value is: 123456
Explanation:
- A Java class named Main is declared with a main method.
- A Scanner object sc is created to read input from the user.
- The program prompts the user to enter a string using System.out.println.
- The input string is read using the sc.nextLine method and stored in the input variable.
- A try-catch block is used to handle a possible NumberFormatException.
- Inside the try block, the Long.valueOf method is used to convert the input string into a long value.
- The converted long value is then displayed on the screen using the System.out.print method.
- If the input string is not a valid representation of a long, a NumberFormatException will be thrown, and the catch block will display an error message “Invalid string.” on the screen.
- The finally block is used to close the Scanner object sc to prevent resource leaks.
3. Convert String to Long Using Long Constructor:
This is similar to the valueOf method, but instead of returning an existing Long object, it creates a new one
Sample code:
import java.util.Scanner;
public class StringToLong {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter a string for long conversion: ");
String input = sc.nextLine();
sc.close();
try {
// Convert the input string to a long value using the valueOf method
long MathNumber = Long.valueOf(input);
System.out.print("The changed string: " + MathNumber);
} catch (NumberFormatException e) {
System.out.printf(" Not a valid string.");
}
}
}
Output:
Enter a string :
123456
The changed string : 123456
Explanation:
- The code imports the java.util.Scanner library
- A public class called “StringToLong” is created
- In the main method, a Scanner object named “sc” is created to read input from the user
- The program prompts the user to enter a string with the message “Enter a string for long conversion: “
- The input string is read and stored in a variable named “input”
- A try-catch block is used to handle any NumberFormatExceptions that may occur during the conversion of the string to a long value
- Inside the try block, the valueOf method of the Long class is used to convert the input string to a long value
- The converted long value is then printed to the screen with the message “The changed string: ” followed by the converted value
- In the catch block, an error message “Not a valid string.” is printed if a NumberFormatException is thrown during the conversion
- In the finally block, the Scanner object “sc” is closed to prevent resource leaks.
4. Change String to Long Using Decimal Format Class:
This method involves converting the string to a BigDecimal object and then to a long value using the longValue() method
Sample code:
import java.text.DecimalFormat;
import java.text.ParseException;
import java.util.Scanner;
public class StringToLong {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter a string: ");
String input = sc.nextLine();
try {
// Create a DecimalFormat object to parse the string into a long value
DecimalFormat df = new DecimalFormat();
Number convertedValue = df.parse(input);
System.out.println("The converted long value is: " + convertedValue.longValue());
} catch (ParseException e) {
System.out.println("Not a valid String input.");
} finally {
sc.close();
}}}
Output:
Enter a string:
123456789
The converted long value is: 123456789
Explanation:
- Import the java.text.DecimalFormat and java.util.Scanner packages
- Create a Scanner object to read input from the user
- Read the input string from the user using the nextLine() method
- Create a DecimalFormat object to parse the string into a long value using the parse() method
- Print the converted long value by calling the longValue() method of the Number object.
- Handle the ParseException that may be thrown during the conversion process and print a custom error message
- Close the Scanner object to prevent resource leaks
Best of the four methods:
For numerous reasons, long.parseLong() is frequently regarded as the finest Java method to turn a string into a long value.
1. Ease of use: It is easy and simple to use. Simply provide the string you wish to convert as an argument, and the programme will return the corresponding long value.
2. Effective: It works quickly and effectively. It has a small overhead and is optimised for translating strings into lengthy values.
3. It is a lightweight way because it doesn’t call for the creation of any new objects.
4. Throws the relevant exceptions: If the input string is not a legitimate representation of a long value, it throws a NumberFormatException. This makes it easier for you to deal with coding problems.
5. High-performance applications that require the quick conversion of strings into lengthy values can use it because of its good performance.
In conclusion, the best way for converting a string into a long value in Java is Long.parseLong() since it is quick, lightweight, efficient, throws the right exceptions, and performs well. When you have a string representation of a long value and you wish to convert it to a long, this is the method of choice for the majority of use cases.
Sample Problems for Converting String Into Long:
1. Long.parseLong(String s) method Sample Problem:
Problem: write a program that will display all the prime numbers till number N and N will be string user input which will be converted to long using the long.parselong() method in java.
Code:
import java.util.Scanner;
public class PrimeNumbers {
// Main method
public static void main(String[] args) {
// Scanner object to read input
Scanner input = new Scanner(System.in);
System.out.print("Enter a number N: ");
String NStr = input.nextLine();
// Converting the string to a long value
long N = Long.parseLong(NStr);
System.out.println("The prime numbers till " + N + " are: ");
// interacting from 2 to N
for (long i = 2; i <= N; i++) {
if (isPrime(i)) {
System.out.println(i);
}}}
public static boolean isPrime(long n) {
if (n <= 1) {
return false;
}
for (long i = 2; i < n; i++) {
if (n % i == 0) {
return false;
}
}return true;}}
Output:
Enter a number N: 20
The prime numbers till 20 are:
2
3
5
7
11
13
17
19
2. Long.valueOf(String s) method Sample Problem:
Problem: write a program that will display the Fibonacci series till number N and N will be string user input which will be converted to long using the long.valueOf() method in java.
Code:
import java.util.Scanner;
public class Fibonacci {
// main method
public static void main(String[] args) {
//Scanner object to read input
Scanner sc = new Scanner(System.in);
System.out.print("Enter the value of N: ");
// read input as string
String input = sc.nextLine();
//parse the string to a long value
long n = Long.valueOf(input);
// values of the two previous numbers
long prev1 = 0, prev2 = 1;
// print the message indicating the series
System.out.print("Fibonacci series up to " + n + ": ");
// loop to generate the series
while (prev1 <= n) {
// calculate the next number in the series
System.out.print(prev1 + " ");
long next = prev1 + prev2;
prev1 = prev2;
prev2 = next;
}
sc.close();
}
}Output:
Enter the value of N: 100
Fibonacci series up to 100: 0 1 1 2 3 5 8 13 21 34 55 89
3. Using Long Constructor Sample Problem:
Problem: write a program in java that will display the factorial of N which will be string user input and will be converted to long using the long constructor.
Code:
import java.util.Scanner;
public class Factorial {
// Main method
public static void main(String[] args) {
// Scanner object to read input
Scanner sc = new Scanner(System.in);
System.out.print("Enter the value of N: ");
// Read the input from the user
String input = sc.nextLine();
// Convert the string to a long value
long n = Long.parseLong(input);
//variable to store the result
long result = 1;
for (long i = 1; i <= n; i++) {
//Multiply the result by the current number
result *= i;
}
//print result
System.out.println("The factorial of " + n + " is " + result);
sc.close();
}
}
Output:
Enter the value of N: 5
The factorial of 5 is 120
4. Decimal Format Class Sample Problem:
Problem: write a code in java that will provide the area of a rectangle and length and breadth will be provided by the user as a string and will be converted into long using decimal format class.
Code:
import java.text.DecimalFormat;
import java.text.ParseException;
import java.util.Scanner;
public class RectangleArea {
// Main method
public static void main(String[] args) throws ParseException {
//Scanner object to read input
Scanner sc = new Scanner(System.in);
//enter the length
System.out.print("Enter the length of the rectangle: ");
// read input as string
String lengthInput = sc.nextLine();
// enter breadth of rectengle
System.out.print("Enter the breadth of the rectangle: ");
// read breadth
String breadthInput = sc.nextLine();
// DecimalFormat object to format the string as long value
DecimalFormat df = new DecimalFormat("#");
// Parse the length input string as a long value
long length = df.parse(lengthInput).longValue();
// Parse the breadth input string as a long value
long breadth = df.parse(breadthInput).longValue();
//Calculate the area of the rectangle
long area = length * breadth;
// print result
System.out.println("The area of the rectangle is: " + area);
sc.close();
}
}
Output:
Enter the length of the rectangle: 10
Enter the breadth of the rectangle: 20
The area of the rectangle is: 200
Conclusion:
In conclusion, there are generally four ways to convert a string to a long in Java, and those are using the Long.parseLong(String) method, Using the Long.valueOf(String) Method, Using Decimal Format Class, and the long constructor. Choosing one method over the other will depend on the specific use case and personal preference.
Regardless of the method used, the result will be a long representation of the string. It is recommended to try each and every method discussed above and use the one with the least time complexity.
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