[Chapter 14] The java.math Package

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| Chapter 14 |

# 14. The java.math Package

Contents:
BigDecimal
BigInteger

The package `java.math` is new as of Java 1.1. It contains two classes that support arithmetic on arbitrarily large integers and floating-point numbers. Figure 14.1 shows the class hierarchy for the `java.math` package.

#### Figure 14.1: The java.math package

# BigDecimal

## Name

BigDecimal

## Synopsis

Class Name:

  `java.math.BigDecimal`

Superclass:

  `java.lang.Number`

Immediate Subclasses:

  None

Interfaces Implemented:

  None

Availability:

  New as of JDK 1.1

## Description

The `BigDecimal` class represents arbitrary-precision rational numbers. A `BigDecimal` object provides a good way to represent a real number that exceeds the range or precision that can be represented by a `double` value or the rounding that is done on a `double` value is unacceptable.

The representation for a `BigDecimal` consists of an unlimited precision integer value and an integer scale factor. The scale factor indicates a power of 10 that the integer value is implicitly divided by. For example, a `BigDecimal` would represent the value 123.456 with an integer value of 123456 and the scale factor of 3. Note that the scale factor cannot be negative and a `BigDecimal` cannot overflow.

Most of the methods in `BigDecimal` perform mathematical operations or make comparisons with other `BigDecimal` objects. Operations that result in some loss of precision, such as division, require a rounding method to be specified. The `BigDecimal` class defines constants to represent the different rounding methods. The rounding method determines if the digit before a discarded fraction is rounded up or left unchanged.

## Class Summary

    public class java.math.BigDecimal extends java.lang.Number {
      // Constants
      public static final int ROUND_CEILING;
      public static final int ROUND_DOWN;
      public static final int ROUND_FLOOR;
      public static final int ROUND_HALF_DOWN;
      public static final int ROUND_HALF_EVEN;
      public static final int ROUND_HALF_UP;
      public static final int ROUND_UNNECESSARY;
      public static final int ROUND_UP;
      // Constructors
      public BigDecimal(double val);
      public BigDecimal(String val);
      public BigDecimal(BigInteger val);
      public BigDecimal(BigInteger val, int scale);
      // Class Methods
      public static BigDecimal valueOf(long val);
      public static BigDecimal valueOf(long val, int scale);
      // Instance Methods
      public BigDecimal abs();
      public BigDecimal add(BigDecimal val);
      public int compareTo(BigDecimal val);
      public BigDecimal divide(BigDecimal val, int roundingMode);
      public BigDecimal divide(BigDecimal val, int scale, int roundingMode);
      public double doubleValue();
      public boolean equals(Object x);
      public float floatValue();
      public int hashCode();
      public int intValue();
      public long longValue();
      public BigDecimal max(BigDecimal val);
      public BigDecimal min(BigDecimal val);
      public BigDecimal movePointLeft(int n);
      public BigDecimal movePointRight(int n);
      public BigDecimal multiply(BigDecimal val);
      public BigDecimal negate();
      public int scale();
      public BigDecimal setScale(int scale);
      public BigDecimal setScale(int scale, int roundingMode);
      public int signum();
      public BigDecimal subtract(BigDecimal val);
      public BigInteger toBigInteger();
      public String toString();
    }

## Constants

### ROUND_CEILING

#### public static final int ROUND_CEILING

Description

  A rounding method that rounds towards positive infinity. Under this method, the value is rounded to the least integer greater than or equal to its value. For example, 2.5 rounds to 3 and -2.5 rounds to -2.

### ROUND_DOWN

#### public static final int ROUND_DOWN

Description

  A rounding method that rounds towards zero by truncating. For example, 2.5 rounds to 2 and -2.5 rounds to -2.

### ROUND_FLOOR

#### public static final int ROUND_FLOOR

Description

  A rounding method that rounds towards negative infinity. Under this method, the value is rounded to the greatest integer less than or equal to its value. For example, 2.5 rounds to 2 and -2.5 rounds to -3.

### ROUND_HALF_DOWN

#### public static final int ROUND_HALF_DOWN

Description

  A rounding method that increments the digit prior to a discarded fraction if the fraction is greater than 0.5; otherwise, the digit is left unchanged. For example, 2.5 rounds to 2, 2.51 rounds to 3, -2.5 rounds to -2, and -2.51 rounds to -3.

### ROUND_HALF_EVEN

#### public static final int ROUND_HALF_EVEN

Description

  A rounding method that behaves like `ROUND_HALF_UP` if the digit prior to the discarded fraction is odd; otherwise it behaves like `ROUND_HALF_DOWN`. For example, 2.5 rounds to 2, 3.5 rounds to 4, -2.5 rounds to -2, and -3.5 rounds to -4.

### ROUND_HALF_UP

#### public static final int ROUND_HALF_UP

Description

  A rounding method that increments the digit prior to a discarded fraction if the fraction is greater than or equal to 0.5; otherwise, the digit is left unchanged. For example, 2.5 rounds to 3, 2.49 rounds to 2, -2.5 rounds to -3, and -2.49 rounds to -2.

### ROUND_UNNECESSARY

#### public static final int ROUND_UNNECESSARY

Description

  A constant that specifies that rounding is not necessary. If the result really does require rounding, an `ArithmeticException` is thrown.

### ROUND_UP

#### public static final int ROUND_UP

Description

  A rounding method that rounds away from zero by truncating. For example, 2.5 rounds to 3 and -2.5 rounds to -3.

## Constructors

### BigDecimal

#### public BigDecimal(double val) throws NumberFormatException

Parameters

  `val`

    The initial value.

Throws

  `NumberFormatException`

    If the `double` has any of the special values: `Double.NEGATIVE_INFINITY`, `Double.POSITIVE_INFINITY`, or `Double.NaN`.

Description

  This constructor creates a `BigDecimal` with the given initial value. The scale of the `BigDecimal` that is created is the smallest value such that (`10^scale x val`) is an integer.

#### public BigDecimal(String val) throws NumberFormatException

Parameters

  `val`

    The initial value.

Throws

  `NumberFormatException`

    If the string cannot be parsed into a valid `BigDecimal`.

Description

  This constructor creates a `BigDecimal` with the initial value specified by the `String`. The string can contain an optional minus sign, followed by zero or more decimal digits, followed by an optional fraction. The fraction must contain a decimal point and zero or more decimal digits. The string must contain as least one digit in the integer or fractional part. The scale of the `BigDecimal` that is created is equal to the number of digits to the right of the decimal point or 0 if there is no decimal point. The mapping from characters to digits is provided by the `Character.digit()` method.

#### public BigDecimal(BigInteger val)

Parameters

  `val`

    The initial value.

Description

  This constructor creates a `BigDecimal` whose initial value comes from the given `BigInteger`. The scale of the `BigDecimal` that is created is 0.

####

     public BigDecimal(BigInteger val, int scale) throws NumberFormatException

Parameters

  `val`

    The initial value.

  `scale`

    The initial scale.

Throws

  `NumberFormatException`

    If `scale` is negative.

Description

  This constructor creates a `BigDecimal` from the given parameters. The `scale` parameter specifies how many digits of the supplied `BigInteger` fall to the right of the decimal point.

## Class Methods

### valueOf

#### public static BigDecimal valueOf(long val)

Parameters

  `val`

    The initial value.

Returns

  A `BigDecimal` that represents the given value.

Description

  This method creates a `BigDecimal` from the given `long` value. The scale of the `BigDecimal` that is created is 0.

####

     public static BigDecimal valueOf(long val, int scale) throws NumberFormatException

Parameters

  `val`

    The initial value.

  `scale`

    The initial scale.

Returns

  A `BigDecimal` that represents the given value and scale.

Throws

  `NumberFormatException`

    If `scale` is negative.

Description

  This method creates a `BigDecimal` from the given parameters. The `scale` parameter specifies how many digits of the supplied `long` fall to the right of the decimal point.

## Instance Methods

### abs

#### public BigDecimal abs()

Returns

  A `BigDecimal` that contains the absolute value of this number.

Description

  This method returns the absolute value of this `BigDecimal`. If this `BigDecimal` is nonnegative, it is returned. Otherwise, a new `BigDecimal` that contains the absolute value of this `BigDecimal` is returned. The scale of the new `BigDecimal` is the same as that of this `BigDecimal`.

### add

#### public BigDecimal add(BigDecimal val)

Parameters

  `val`

    The number to be added.

Returns

  A new `BigDecimal` that contains the sum of this number and the given value.

Description

  This method returns the sum of this `BigDecimal` and the given `BigDecimal` as a new `BigDecimal`. The value of the new `BigDecimal` is the sum of the values of the two `BigDecimal` objects being added; the scale is the maximum of their two scales.

### compareTo

#### public int compareTo(BigDecimal val)

Parameters

  `val`

    The number to be compared.

Returns

  `-1` if this number is less than `val`, `0` if this number is equal to `val`, or `1` if this number is greater than `val`.

Description

  This method compares this `BigDecimal` to the given`BigDecimal` and returns a value that indicates the result of the comparison. The method considers two `BigDecimal` objects that have the same values but different scales to be equal. This method can be used to implement all six of the standard boolean comparison operators: `==`, `!=`, `<=`, `<`, `>=`, and `>`.

### divide

####

     public BigDecimal divide(BigDecimal val, int roundingMode) throws ArithmeticException, IllegalArgumentException

Parameters

  `val`

    The divisor.

  `roundingMode`

    The rounding mode.

Returns

  A new `BigDecimal` that contains the result (quotient) of dividing this number by the supplied value.

Throws

  `ArithmeticException`

    If `val` is `0`, or if `ROUND_UNNECESSARY` is specified for the rounding mode but rounding is necessary.

  `IllegalArgumentException`

    If `roundingMode` is not a valid value.

Description

  This method returns the quotient that results from dividing this `BigDecimal` by the given `BigDecimal` and applying the specified rounding mode. The quotient is returned as a new `BigDecimal` that has the same scale as the scale of this `BigDecimal` scale. One of the rounding constants must be specified for the rounding mode.

####

     public BigDecimal divide(BigDecimal val, int scale, int roundingMode) throws ArithmeticException, IllegalArgumentException

Parameters

  `val`

    The divisor.

  `scale`

    The scale for the result.

  `roundingMode`

    The rounding mode.

Returns

  A new `BigDecimal` that contains the result (quotient) of dividing this number by the supplied value.

Throws

  `ArithmeticException`

    If `val` is `0`, if `scale` is less than zero, or if `ROUND_UNNECESSARY` is specified for the rounding mode but rounding is necessary.

  `IllegalArgumentException`

    If `roundingMode` is not a valid value.

Description

  This method returns the quotient that results from dividing dividing this `BigDecimal` by the given `BigDecimal` and applying the specified rounding mode. The quotient is returned as a new `BigDecimal` that has the given scale. One of the rounding constants must be specified for the rounding mode.

### doubleValue

#### public double doubleValue()

Returns

  The value of this `BigDecimal` as a `double`.

Overrides

  `Number.doubleValue()`

Description

  This method returns the value of this `BigDecimal` as a `double`. If the value exceeds the limits of a `double`, `Double.POSITIVE_INFINITY` or `Double.NEGATIVE_INFINITY` is returned.

### equals

#### public boolean equals(Object x)

Parameters

  `x`

    The object to be compared with this object.

Returns

  `true` if the objects are equal; `false` if they are not.

Overrides

  `Object``.equals()`

Description

  This method returns `true` if `x` is an instance of `BigDecimal`, and it represents the same value as this `BigDecimal`. In order to be considered equal using this method, two `BigDecimal` objects must have the same values and scales.

### floatValue

#### public float floatValue()

Returns

  The value of this `BigDecimal` as a `float`.

Overrides

  `Number.floatValue()`

Description

  This method returns the value of this `BigDecimal` as a `float`. If the value exceeds the limits of a `float`, `Float.POSITIVE_INFINITY` or `Float.NEGATIVE_INFINITY` is returned.

### hashCode

#### public int hashCode()

Returns

  A hashcode for this object.

Overrides

  `Object``.hashCode()`

Description

  This method returns a hashcode for this `BigDecimal`.

### intValue

#### public int intValue()

Returns

  The value of this `BigDecimal` as an `int`.

Overrides

  `Number.intValue()`

Description

  This method returns the value of this `BigDecimal` as an `int`. If the value exceeds the limits of an `int`, the excessive high-order bits are discarded. Any fractional part of this `BigDecimal` is truncated.

### longValue

#### public long longValue()

Returns

  The value of this `BigDecimal` as a `long`.

Overrides

  `Number.longValue()`

Description

  This method returns the value of this `BigDecimal` as a `long`. If the value exceeds the limits of a `long`, the excessive high-order bits are discarded. Any fractional part of this `BigDecimal` is also truncated.

### max

#### public BigDecimal max(BigDecimal val)

Parameters

  `val`

    The number to be compared.

Returns

  The `BigDecimal` that represents the greater of this number and the given value.

Description

  This method returns the greater of this `BigDecimal` and the given `BigDecimal`.

### min

#### public BigDecimal min(BigDecimal val)

Parameters

  `val`

    The number to be compared.

Returns

  The `BigDecimal` that represents the lesser of this number and the given value.

Description

  This method returns the lesser of this `BigDecimal` and the given `BigDecimal`.

### movePointLeft

#### public BigDecimal movePointLeft(int n)

Parameters

  `n`

    The number of digits to move the decimal point to the left.

Returns

  A new `BigDecimal` that contains the adjusted number.

Description

  This method returns a `BigDecimal` that is computed by shifting the decimal point of this `BigDecimal` left by the given number of digits. If `n` is nonnegative, the value of the new `BigDecimal` is the same as the current value, and the scale is increased by `n`. If `n` is negative, the method call is equivalent to `movePointRight(-n)`.

### movePointRight

#### public BigDecimal movePointRight(int n)

Parameters

  `n`

    The number of digits to move the decimal point to the right.

Returns

  A new `BigDecimal` that contains the adjusted number.

Description

  This method returns a `BigDecimal` that is computed by shifting the decimal point of this `BigDecimal` right by the given number of digits. If `n` is nonnegative, the value of the new `BigDecimal` is the same as the current value, and the scale is decreased by `n`. If `n` is negative, the method call is equivalent to `movePointLeft(-n)`.

### multiply

#### public BigDecimal multiply(BigDecimal val)

Parameters

  `val`

    The number to be multiplied.

Returns

  A new `BigDecimal` that contains the product of this number and the given value.

Description

  This method multiplies this `BigDecimal` and the given `BigDecimal`, and returns the result as a new `BigDecimal`. The value of the new `BigDecimal` is the product of the values of the two `BigDecimal` objects being added; the scale is the sum of their two scales.

### negate

#### public BigDecimal negate()

Returns

  A new `BigDecimal` that contains the negative of this number.

Description

  This method returns a new `BigDecimal` that is identical to this `BigDecimal` except that its sign is reversed. The scale of the new `BigDecimal` is the same as the scale of this `BigDecimal`.

### scale

#### public int scale()

Returns

  The scale of this number.

Description

  This method returns the scale of this`BigDecimal`.

### setScale

####

     public BigDecimal setScale(int scale) throws ArithmeticException, IllegalArgumentException

Parameters

  `scale`

    a The new scale.

Returns

  A new `BigDecimal` that is identical to this number, except that is has the given scale.

Throws

  `ArithmeticException`

    If the new number cannot be calculated without rounding.

  `IllegalArgumentException`

    This exception is never thrown.

Description

  This method creates a new `BigDecimal` that has the given scale and a value that is calculated by multiplying or dividing the value of this `BigDecimal` by the appropriate power of 10 to maintain the overall value. The method is typically used to increase the scale of a number, not decrease it. It can decrease the scale, however, if there are enough zeros in the fractional part of the value to allow for rescaling without loss of precision.

  Calling this method is equivalent to calling `setScale(scale,` `BigDecimal.ROUND_UNNECESSARY)`.

####

     public BigDecimal setScale(int scale, int roundingMode) throws ArithmeticException, IllegalArgumentException

Parameters

  `scale`

    The new scale.

  `roundingMode`

    The rounding mode.

Returns

  A new `BigDecimal` that contains this number adjusted to the given scale.

Throws

  `ArithmeticException`

    If `scale` is less than zero, or if `ROUND_UNNECESSARY` is specified for the rounding mode but rounding is necessary.

  `IllegalArgumentException`

    If `roundingMode` is not a valid value.

Description

  This method creates a new `BigDecimal` that has the given scale and a value that is calculated by multiplying or dividing the value of this `BigDecimal` by the appropriate power of 10 to maintain the overall value. When the scale is reduced, the value must be divided, so precision may be lost. In this case, the specified rounding mode is used.

### signum

#### public int signum()

Returns

  `-1` if this number is negative, `0` if this number is zero, or `1` if this number is positive.

Description

  This method returns a value that indicates the sign of this `BigDecimal`.

### subtract

#### public BigDecimal subtract(BigDecimal val)

Parameters

  `val`

    The number to be subtracted.

Returns

  A new `BigDecimal` that contains the result of subtracting the given number from this number.

Description

  This method subtracts the given `BigDecimal` from this `BigDecimal` and returns the result as a new `BigDecimal`. The value of the new `BigDecimal` is the result of subtracting the value of the given `BigDecimal` from this `BigDecimal`; the scale is the maximum of their two scales.

### toBigInteger

#### public BigInteger toBigInteger()

Returns

  The value of this `BigDecimal` as a `BigInteger`.

Description

  This method returns the value of this `BigDecimal` as a `BigInteger`. The fractional part of this number is truncated.

### toString

#### public String toString()

Returns

  A string representation of this object.

Overrides

  `Object.toString()`

Description

  This method returns a string representation of this `BigDecimal`. A minus sign represents the sign, and a decimal point is used to represent the scale. The mapping from digits to characters is provided by the `Character.forDigit()` method.

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`byteValue()` | `Number` | `clone()` | `Object`
`getClass()` | `Object` | `finalize()` | `Object`
`notify()` | `Object` | `notifyAll()` | `Object`
`shortValue()` | `Number` | `wait()` | `Object`
`wait(long)` | `Object` | `wait(long, int)` | `Object`

## See Also

`ArithmeticException`, `BigInteger`, `Character`, `Double`, `Float`, `IllegalArgumentException`, `Integer`, `Long`, `Number`, `NumberFormatException`

Modifier |  | BigInteger