Rounding a double value to a specific number of decimal places is a common task in programming, especially when dealing with monetary values. Java provides several methods to perform this task, and in this article, we will discuss how to round a double to 2 decimal places in Java with code examples.

Here are the ways to round a double to 2 decimal places in Java:

- Math.round() method

The Math.round() method is a standard library method in Java that returns the closest long to the argument, with ties rounding to positive infinity. We can use this method to round a double to 2 decimal places by multiplying the double value by 100, rounding it to the nearest integer, and then dividing it by 100.

Here's an example of how to use the Math.round() method to round a double to 2 decimal places:

```
double num = 123.45678;
long factor = (long) Math.pow(10, 2);
num = num * factor;
double rounded = (double) Math.round(num) / factor;
System.out.println("Rounded to 2 decimal places: " + rounded);
```

The output will be:

```
Rounded to 2 decimal places: 123.46
```

- DecimalFormat class

The DecimalFormat class is a class that formats a number to a string representation following a specific pattern. We can use this class to round a double to 2 decimal places by defining a pattern that includes only 2 decimal places and then using the format() method to format the double value.

Here's an example of how to use the DecimalFormat class to round a double to 2 decimal places:

```
double num = 123.45678;
DecimalFormat df = new DecimalFormat("#.00");
String rounded = df.format(num);
System.out.println("Rounded to 2 decimal places: " + rounded);
```

The output will be:

```
Rounded to 2 decimal places: 123.46
```

- BigDecimal class

The BigDecimal class is a class that provides arbitrary-precision decimal arithmetic. We can use this class to round a double to 2 decimal places by creating a BigDecimal object from the double value and then using the setScale() method to set the number of decimal places.

Here's an example of how to use the BigDecimal class to round a double to 2 decimal places:

```
double num = 123.45678;
BigDecimal bd = new BigDecimal(num);
bd = bd.setScale(2, RoundingMode.HALF_UP);
double rounded = bd.doubleValue();
System.out.println("Rounded to 2 decimal places: " + rounded);
```

The output will be:

```
Rounded to 2 decimal places: 123.46
```

In conclusion, rounding a double to 2 decimal places in Java can be done using the Math.round() method, the DecimalFormat class, or the BigDecimal class. Each method has its advantages and disadvantages, and the choice of which method to use depends on the specific requirements of your project.

Rounding Modes:

One important aspect to consider when rounding a double to a specific number of decimal places is the rounding mode. The rounding mode determines the rule to be used when rounding is required.

Java provides several rounding modes that can be used with the setScale() method of the BigDecimal class or with the RoundingMode enumeration:

- RoundingMode.UP: Rounds away from zero.
- RoundingMode.DOWN: Rounds towards zero.
- RoundingMode.CEILING: Rounds towards positive infinity.
- RoundingMode.FLOOR: Rounds towards negative infinity.
- RoundingMode.HALF_UP: Rounds towards the nearest integer, rounding away from zero if the decimal part is exactly 0.5.
- RoundingMode.HALF_DOWN: Rounds towards the nearest integer, rounding towards zero if the decimal part is exactly 0.5.
- RoundingMode.HALF_EVEN: Rounds towards the nearest integer, rounding towards the even integer if the decimal part is exactly 0.5.

When rounding a double to 2 decimal places, the most common rounding mode to use is RoundingMode.HALF_UP, as this will round up when the decimal part is exactly 0.5.

Precision:

When rounding a double to a specific number of decimal places, it's important to note that the resulting value may not be exactly what you expect due to the limitations of floating-point arithmetic.

In most cases, this is not a problem, as the difference is usually very small and can be ignored. However, in some cases, it may be necessary to use a different data type that provides greater precision, such as the BigDecimal class.

When using the BigDecimal class, it's important to keep in mind that the setScale() method returns a new BigDecimal object and does not modify the original object. This means that you'll need to assign the result of the setScale() method to a new variable or update the original object.

Performance:

The performance of the different methods for rounding a double to 2 decimal places can vary depending on the specific requirements of your project.

In general, the Math.round() method is the fastest, followed by the DecimalFormat class, and the BigDecimal class is the slowest.

If performance is a concern, it's recommended to use the Math.round() method or the DecimalFormat class for small numbers of values. For large numbers of values, the BigDecimal class can be used, although it may be necessary to use an optimized implementation or consider using a different data type that provides better performance.

In conclusion, rounding a double to 2 decimal places in Java is a common task that can be performed using several methods. When choosing a method, it's important to consider the rounding mode, precision, and performance, as well as the specific requirements of your project.

## Popular questions

- What are the different methods to round a double to 2 decimal places in Java?

There are several methods to round a double to 2 decimal places in Java, including using the Math.round() method, the DecimalFormat class, or the BigDecimal class.

- What is the fastest method to round a double to 2 decimal places in Java?

The fastest method to round a double to 2 decimal places in Java is the Math.round() method.

- What is the most precise method to round a double to 2 decimal places in Java?

The most precise method to round a double to 2 decimal places in Java is the BigDecimal class.

- How do you specify the rounding mode when rounding a double to 2 decimal places in Java?

The rounding mode can be specified by using the setScale() method of the BigDecimal class with one of the RoundingMode enumeration values, or by using the RoundingMode enumeration with the Math.round() method.

- Do the different methods for rounding a double to 2 decimal places in Java modify the original value or return a new value?

The Math.round() method returns a new value, while the DecimalFormat class returns a new String object. The BigDecimal class returns a new BigDecimal object and does not modify the original object.

### Tag

Rounding.