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Java Fundamental Classes Reference

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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.

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


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