In Java, it’s common to work with numeric values in the form of decimals, and sometimes these values are provided as Strings. When working with Strings that represent decimal values, it’s often necessary to convert them to Decimal values to perform arithmetic operations or store them in a database.
Here we will discuss how to convert a String to a Decimal in Java. We will cover different methods of converting Strings to Decimals, including using the BigDecimal class, DecimalFormat class, NumberFormat class and Double.parseDouble() method.
Why is there a need to convert string to decimal in java?
There are many reasons why you might need to convert a String to a decimal in Java.
- Avoiding Data Errors:When working with financial or mathematical applications, accuracy is critical, and even small errors can lead to significant problems.
- Performing Arithmetic Operations:Converting a String to a Decimal is also necessary when performing arithmetic operations such as addition, subtraction, multiplication, or division. While Java can perform arithmetic operations on Strings, these operations are not always reliable or efficient.
In contrast, Decimal values are designed for numerical calculations and are much more reliable and efficient. - Storing Data in a Database:Many databases require numeric values to be stored as Decimal or other numeric types, and storing a String value directly in the database can lead to errors. By converting the String to a Decimal before storing it in the database, we ensure that the data is in the correct format and can be used efficiently
Four Methods for converting string to decimal in Java:
There are several ways to convert a string to decimal in Java:
- Using the BigDecimal class
- Using the DecimalFormat class
- Using the NumberFormat class
- Using the Double.parseDouble() method
A thorough explanation of each strategy about how to convert string to decimal in Java:
1.BigDecimal class method to convert string to decimal
To convert a String to a BigDecimal, you can use the BigDecimal(String) constructor, which creates a new BigDecimal instance from the specified String.
Sample Code:
import java.math.BigDecimal;
public class StringToDecimalExample {
public static void main(String[] args) {
// String containing decimal value
String str = "123.456";
// Convert String to Decimal using BigDecimal
BigDecimal decimal = new BigDecimal(str);
// Print the Decimal value
System.out.println(decimal);
}
}Output:
123.456Code Explanation:
- The code imports the java.math.BigDecimal class to use for converting the String to a Decimal.
- A new class named StringToDecimalExample is defined.
- The public static void main(String[] args) method is the starting point of the program where execution begins.
- A new String object named str is initialized with the value “123.456”, which is the String we want to convert to a Decimal.
- A new BigDecimal object named decimal is created by passing the str String to the BigDecimal constructor.
- The System.out.println(decimal) statement prints the decimal value to the console using the println() method.
2. DecimalFormat method to change string to decimal in Java:
The DecimalFormat class is a subclass of NumberFormat that allows you to format decimal values according to a specified pattern. To convert a String to a decimal using DecimalFormat, you first create a new DecimalFormat instance with the desired pattern, and then use the parse(String) method to parse the String and return a Number object, which you can then cast to a BigDecimal.
Sample Code:
import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.text.ParseException;
public class StringToDecimalExample {
public static void main(String[] args) throws ParseException {
// String containing decimal value
String str = "123.456";
// Convert String to Decimal using DecimalFormat
DecimalFormat decimalFormat = new DecimalFormat();
BigDecimal decimal = new BigDecimal(decimalFormat.parse(str).toString());
// Print the Decimal value
System.out.println(decimal);
}
}Output:
123.456Code Explanation:
- The program initializes a String object with the decimal value.
- A new DecimalFormat object is created, which will be used to parse the String object into a BigDecimal.
- The parse() method of the DecimalFormat object is called with the String object as a parameter, which returns a Number object.
- The toString() method of the Number object is called to get a String representation of the decimal value.
- The BigDecimal constructor is called with the String representation of the decimal value to create a new BigDecimal object.
- The BigDecimal object is printed to the console using the println() method.
3. Change String to decimal using NumberFormat class:
The NumberFormat class is an abstract class that provides a common interface for formatting and parsing numeric values. You can use the getNumberInstance() method to obtain a NumberFormat object that is specific to the default locale, and then use the parse(String) method to convert the String to a Number object.
Sample Code:
import java.math.BigDecimal;
import java.text.NumberFormat;
import java.text.ParseException;
public class StringToDecimalExample {
public static void main(String[] args) throws ParseException {
// String containing decimal value
String str = "123.456";
// Convert String to Decimal using NumberFormat
NumberFormat numberFormat = NumberFormat.getInstance();
BigDecimal decimal = new BigDecimal(numberFormat.parse(str).toString());
// Print the Decimal value
System.out.println(decimal);
}
}Output:
123.456Code Explanation:
- We first define a String variable str containing a decimal value “123.45”.
- We then create an instance of the NumberFormat class using the getInstance() method. This will return a NumberFormat object that can be used to parse the String value.
- We then use the parse() method of the NumberFormat object to convert the String value to a Number object, and then convert that to a BigDecimal object using the toString() method.
- Finally, we print the resulting BigDecimal object to the console using System.out.println().
4. Convert String to decimal using Double.parseDouble() method:
In Java, the Double class provides a simple method for converting a String to a decimal value: Double.parseDouble(). This method takes a String input and returns a double value representing the numeric value of the String.
Sample Code:
import java.math.BigDecimal;
public class StringToDecimalExample {
public static void main(String[] args) {
// String containing decimal value
String str = "123.456";
// Convert String to Decimal using Double.parseDouble()
BigDecimal decimal = BigDecimal.valueOf(Double.parseDouble(str));
// Print the Decimal value
System.out.println(decimal);
}
}Output:
123.456Code Explanation:
- We first define a String variable str containing a decimal value “123.456”.
- We then use the Double.parseDouble() method to parse the String value and convert it to a double value.
- We then use the BigDecimal.valueOf() method to convert the double value to a BigDecimal object.
- Finally, we print the resulting BigDecimal object to the console using System.out.println().
Best of the four methods:
For numerous reasons,the BigDecimal class is regarded as the finest java method to turn a string into a decimal.
- Precision and accuracy: The BigDecimal class provides the highest level of precision and accuracy, making it the best choice for applications where exact decimal values are critical.
- Range of operations: The BigDecimal class provides a range of methods for performing arithmetic operations, rounding, comparison, and more. This makes it a powerful tool for performing complex mathematical operations.
- Stability and reliability: BigDecimal is a stable and well-tested class that has been available in Java since version 1.1. This means that it has been thoroughly tested and is widely used, making it a reliable and trustworthy option.
- Flexible formatting: The BigDecimal class provides options for formatting decimal values, such as the number of decimal places and the use of rounding. This flexibility makes it a good choice for applications that require precise formatting of decimal values.
Sample Problems for Converting string to decimal in Java:
1. BigDecimal method Sample Problem:
Problem:
Write a Java program that converts a String representation of a decimal number to a BigDecimal object using the BigDecimal class.
Solution:
- In the code, a string value “1234.5678” is assigned to a variable named decimalString.
- The new BigDecimal(decimalString) statement creates a new BigDecimal object by passing the string value decimalString as an argument.
- The BigDecimal constructor can handle strings with decimal point, exponent, and thousands separators.
- The resulting BigDecimal object is assigned to a variable named decimal.
- Finally, the value of the BigDecimal object is printed to the console using the System.out.println() statement.
Code:
import java.math.BigDecimal;
public class StringToBigDecimalExample {
public static void main(String[] args) {
String decimalString = "1234.5678";
BigDecimal decimal = new BigDecimal(decimalString);
System.out.println("Decimal value: " + decimal);
}
}Output:
Decimal value: 1234.56782. DecimalFormat method Sample Problem:
Problem:
Convert the following String value to Decimal using the DecimalFormat class:
- “123.45”
Solution:
- Declare a String variable ‘str’ with the value “123.45”.
- Create a DecimalFormat object with the pattern “#.##”. This specifies that we want to round to two decimal places.
- Use the format() method of the DecimalFormat class to format the String value ‘str’ to a Decimal value with two decimal places. The format() method returns a String representation of the formatted value.
- Then, use the parseDouble() method of the Double class to convert the formatted String value to a Double value.
- Print the Decimal value to the console.
Code:
import java.text.DecimalFormat;
public class StringToDecimalExample {
public static void main(String[] args) {
// String containing decimal value
String str = "123.45";
// Create DecimalFormat object with appropriate pattern
DecimalFormat decimalFormat = new DecimalFormat("#.##");
// Convert String to Decimal using DecimalFormat
double decimal = Double.parseDouble(decimalFormat.format(Double.parseDouble(str)));
// Print the Decimal value
System.out.println(decimal);
}
}Output:
123.453. NumberFormat method Sample Problem:
Problem:
Write a Java program that prompts the user to enter a decimal number as a String, and converts it to a decimal using the NumberFormat class.
Solution:
- The program prompts the user to input a decimal number as a string using the Scanner class.
- The input string is stored in a variable named “decimalString”.
- The program uses a try-catch block to handle any exceptions that may occur during parsing.
- The NumberFormat class is used to convert the input string to a number.
- The parse method of NumberFormat returns a Number object which is then converted to a double using the doubleValue method.
- The resulting double value is stored in a variable named “decimal”.
- The program then prints the value of “decimal” to the console using the println method.
Code:
import java.text.NumberFormat;
import java.util.Scanner;
public class StringToDecimalExample {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter a decimal number: ");
String decimalString = scanner.next();
try {
double decimal = NumberFormat.getInstance().parse(decimalString).doubleValue();
System.out.println("Decimal value: " + decimal);
} catch (Exception e) {
System.out.println("Invalid input: " + e.getMessage());
}
}
}Output:
Enter a decimal number: 55.666
Decimal value: 55.6664. Double.parseDouble() method Sample Problem:
Problem:
How can you use the Double.parseDouble() method in Java to convert a user input decimal number from String to decimal. Write a program to implement this.
Solution:
- First, the program prompts the user to enter a decimal number as a String using the Scanner class.
- Then, the program uses the Double.parseDouble() method to convert the String to a double.
- If the input is not a valid decimal number, the program catches the NumberFormatException and prints an error message.
Code:
import java.util.Scanner;
public class StringToDoubleExample {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter a decimal number: ");
String decimalString = scanner.next();
try {
double decimal = Double.parseDouble(decimalString);
System.out.println("Decimal value: " + decimal);
} catch (NumberFormatException e) {
System.out.println("Invalid input: " + e.getMessage());
}
}
}Output:
Enter a decimal number: 55.6666
Decimal value: 55.6666Conclusion:
In this blog post, we learned how to convert a string to decimal in java .Converting a string value to a decimal can be achieved using several methods like BigDecimal class, DecimalFormat class, NumberFormat class and Double.parseDouble() method. However, after examining the advantages of each approach, it’s clear that BigDecimal class is the best option to use.
Also, the other methods can be useful in certain situations. When choosing a method, consider which one is the most appropriate for your use case.
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