org.apache.commons.lang3

Class BitField

java.lang.Object

org.apache.commons.lang3.BitField

public class BitField
extends java.lang.Object

Supports operations on bit-mapped fields. Instances of this class can be used to store a flag or data within an int, short or byte.

Each BitField is constructed with a mask value, which indicates the bits that will be used to store and retrieve the data for that field. For instance, the mask 0xFF indicates the least-significant byte should be used to store the data.

As an example, consider a car painting machine that accepts paint instructions as integers. Bit fields can be used to encode this:

    // blue, green and red are 1 byte values (0-255) stored in the three least
    // significant bytes
    BitField blue = new BitField(0xFF);
    BitField green = new BitField(0xFF00);
    BitField red = new BitField(0xFF0000);

    // anyColor is a flag triggered if any color is used
    BitField anyColor = new BitField(0xFFFFFF);

    // isMetallic is a single bit flag
    BitField isMetallic = new BitField(0x1000000);

Using these BitField instances, a paint instruction can be encoded into an integer:

    int paintInstruction = 0;
    paintInstruction = red.setValue(paintInstruction, 35);
    paintInstruction = green.setValue(paintInstruction, 100);
    paintInstruction = blue.setValue(paintInstruction, 255);

Flags and data can be retrieved from the integer:

    // Prints true if red, green or blue is non-zero
    System.out.println(anyColor.isSet(paintInstruction));   // prints true

    // Prints value of red, green and blue
    System.out.println(red.getValue(paintInstruction));     // prints 35
    System.out.println(green.getValue(paintInstruction));   // prints 100
    System.out.println(blue.getValue(paintInstruction));    // prints 255

    // Prints true if isMetallic was set
    System.out.println(isMetallic.isSet(paintInstruction)); // prints false

Since:

2.0

Constructor Summary

Constructors

Constructor and Description
BitField(int mask) Creates a BitField instance.

Method Summary

Modifier and Type	Method and Description
int	clear(int holder) Clears the bits.
byte	clearByte(byte holder) Clears the bits.
short	clearShort(short holder) Clears the bits.
int	getRawValue(int holder) Obtains the value for the specified BitField, unshifted.
short	getShortRawValue(short holder) Obtains the value for the specified BitField, unshifted.
short	getShortValue(short holder) Obtains the value for the specified BitField, appropriately shifted right, as a short.
int	getValue(int holder) Obtains the value for the specified BitField, appropriately shifted right.
boolean	isAllSet(int holder) Returns whether all of the bits are set or not.
boolean	isSet(int holder) Returns whether the field is set or not.
int	set(int holder) Sets the bits.
int	setBoolean(int holder, boolean flag) Sets a boolean BitField.
byte	setByte(byte holder) Sets the bits.
byte	setByteBoolean(byte holder, boolean flag) Sets a boolean BitField.
short	setShort(short holder) Sets the bits.
short	setShortBoolean(short holder, boolean flag) Sets a boolean BitField.
short	setShortValue(short holder, short value) Replaces the bits with new values.
int	setValue(int holder, int value) Replaces the bits with new values.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BitField

public BitField(int mask)

Creates a BitField instance.

Parameters:

mask - the mask specifying which bits apply to this BitField. Bits that are set in this mask are the bits that this BitField operates on

Method Detail

getValue

public int getValue(int holder)

Obtains the value for the specified BitField, appropriately shifted right.

Many users of a BitField will want to treat the specified bits as an int value, and will not want to be aware that the value is stored as a BitField (and so shifted left so many bits).

Parameters:

holder - the int data containing the bits we're interested in

Returns:

the selected bits, shifted right appropriately

See Also:

setValue(int,int)

getShortValue

public short getShortValue(short holder)

Obtains the value for the specified BitField, appropriately shifted right, as a short.

Many users of a BitField will want to treat the specified bits as an int value, and will not want to be aware that the value is stored as a BitField (and so shifted left so many bits).

Parameters:

holder - the short data containing the bits we're interested in

Returns:

the selected bits, shifted right appropriately

See Also:

setShortValue(short,short)

getRawValue

public int getRawValue(int holder)

Obtains the value for the specified BitField, unshifted.

Parameters:

holder - the int data containing the bits we're interested in

Returns:

the selected bits

getShortRawValue

public short getShortRawValue(short holder)

Obtains the value for the specified BitField, unshifted.

Parameters:

holder - the short data containing the bits we're interested in

Returns:

the selected bits

isSet

public boolean isSet(int holder)

Returns whether the field is set or not.

This is most commonly used for a single-bit field, which is often used to represent a boolean value; the results of using it for a multi-bit field is to determine whether *any* of its bits are set.

Parameters:

holder - the int data containing the bits we're interested in

Returns:

true if any of the bits are set, else false

isAllSet

public boolean isAllSet(int holder)

Returns whether all of the bits are set or not.

This is a stricter test than isSet(int), in that all of the bits in a multi-bit set must be set for this method to return true.

Parameters:

holder - the int data containing the bits we're interested in

Returns:

true if all of the bits are set, else false

setValue

public int setValue(int holder,
                    int value)

Replaces the bits with new values.

Parameters:

holder - the int data containing the bits we're interested in

value - the new value for the specified bits

Returns:

the value of holder with the bits from the value parameter replacing the old bits

See Also:

getValue(int)

setShortValue

public short setShortValue(short holder,
                           short value)

Replaces the bits with new values.

Parameters:

holder - the short data containing the bits we're interested in

value - the new value for the specified bits

Returns:

the value of holder with the bits from the value parameter replacing the old bits

See Also:

getShortValue(short)

clear

public int clear(int holder)

Clears the bits.

Parameters:

holder - the int data containing the bits we're interested in

Returns:

the value of holder with the specified bits cleared (set to 0)

clearShort

public short clearShort(short holder)

Clears the bits.

Parameters:

holder - the short data containing the bits we're interested in

Returns:

the value of holder with the specified bits cleared (set to 0)

clearByte

public byte clearByte(byte holder)

Clears the bits.

Parameters:

holder - the byte data containing the bits we're interested in

Returns:

the value of holder with the specified bits cleared (set to 0)

set

public int set(int holder)

Sets the bits.

Parameters:

holder - the int data containing the bits we're interested in

Returns:

the value of holder with the specified bits set to 1

setShort

public short setShort(short holder)

Sets the bits.

Parameters:

holder - the short data containing the bits we're interested in

Returns:

the value of holder with the specified bits set to 1

setByte

public byte setByte(byte holder)

Sets the bits.

Parameters:

holder - the byte data containing the bits we're interested in

Returns:

the value of holder with the specified bits set to 1

setBoolean

public int setBoolean(int holder,
                      boolean flag)

Sets a boolean BitField.

Parameters:

holder - the int data containing the bits we're interested in

flag - indicating whether to set or clear the bits

Returns:

the value of holder with the specified bits set or cleared

setShortBoolean

public short setShortBoolean(short holder,
                             boolean flag)

Sets a boolean BitField.

Parameters:

holder - the short data containing the bits we're interested in

flag - indicating whether to set or clear the bits

Returns:

the value of holder with the specified bits set or cleared

setByteBoolean

public byte setByteBoolean(byte holder,
                           boolean flag)

Sets a boolean BitField.

Parameters:

holder - the byte data containing the bits we're interested in

flag - indicating whether to set or clear the bits

Returns:

the value of holder with the specified bits set or cleared