# Class CommandAPDU

java.lang.Object
javax.smartcardio.CommandAPDU

All Implemented Interfaces:
  `Serializable`

public final class CommandAPDU extends Object implements Serializable
A command APDU following the structure defined in ISO/IEC 7816-4. It consists of a four byte header and a conditional body of variable length. This class does not attempt to verify that the APDU encodes a semantically valid command.

Note that when the expected length of the response APDU is specified in the constructors, the actual length (Ne) must be specified, not its encoded form (Le). Similarly, getNe() returns the actual value Ne. In other words, a value of 0 means "no data in the response APDU" rather than "maximum length."

This class supports both the short and extended forms of length encoding for Ne and Nc. However, note that not all terminals and Smart Cards are capable of accepting APDUs that use the extended form.

For the header bytes CLA, INS, P1, and P2 the Java type `int` is used to represent the 8 bit unsigned values. In the constructors, only the 8 lowest bits of the `int` value specified by the application are significant. The accessor methods always return the byte as an unsigned value between 0 and 255.

Instances of this class are immutable. Where data is passed in or out via byte arrays, defensive cloning is performed.

Since:
  1.6
See Also:
  - `ResponseAPDU`
  - `CardChannel.transmit`
  - Serialized Form

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `CommandAPDU(byte[] apdu)`
  Constructs a CommandAPDU from a byte array containing the complete APDU contents (header and body).
  `CommandAPDU(byte[] apdu, int apduOffset, int apduLength)`
  Constructs a CommandAPDU from a byte array containing the complete APDU contents (header and body).
  `CommandAPDU(int cla, int ins, int p1, int p2)`
  Constructs a CommandAPDU from the four header bytes.
  `CommandAPDU(int cla, int ins, int p1, int p2, byte[] data)`
  Constructs a CommandAPDU from the four header bytes and command data.
  `CommandAPDU(int cla, int ins, int p1, int p2, byte[] data, int ne)`
  Constructs a CommandAPDU from the four header bytes, command data, and expected response data length.
  `CommandAPDU(int cla, int ins, int p1, int p2, byte[] data, int dataOffset, int dataLength)`
  Constructs a CommandAPDU from the four header bytes and command data.
  `CommandAPDU(int cla, int ins, int p1, int p2, byte[] data, int dataOffset, int dataLength, int ne)`
  Constructs a CommandAPDU from the four header bytes, command data, and expected response data length.
  `CommandAPDU(int cla, int ins, int p1, int p2, int ne)`
  Constructs a CommandAPDU from the four header bytes and the expected response data length.
  `CommandAPDU(ByteBuffer apdu)`
  Creates a CommandAPDU from the ByteBuffer containing the complete APDU contents (header and body).

- ## Method Summary

  Modifier and Type
  Method
  Description
  `boolean`
  `equals(Object obj)`
  Compares the specified object with this command APDU for equality.
  `byte[]`
  `getBytes()`
  Returns a copy of the bytes in this APDU.
  `int`
  `getCLA()`
  Returns the value of the class byte CLA.
  `byte[]`
  `getData()`
  Returns a copy of the data bytes in the command body.
  `int`
  `getINS()`
  Returns the value of the instruction byte INS.
  `int`
  `getNc()`
  Returns the number of data bytes in the command body (Nc) or 0 if this APDU has no body.
  `int`
  `getNe()`
  Returns the maximum number of expected data bytes in a response APDU (Ne).
  `int`
  `getP1()`
  Returns the value of the parameter byte P1.
  `int`
  `getP2()`
  Returns the value of the parameter byte P2.
  `int`
  `hashCode()`
  Returns the hash code value for this command APDU.
  `String`
  `toString()`
  Returns a string representation of this command APDU.

  ### Methods declared in class Object

  `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- ## Constructor Details

  - ### CommandAPDU

    public CommandAPDU(byte[] apdu)
    Constructs a CommandAPDU from a byte array containing the complete APDU contents (header and body).

    Note that the apdu bytes are copied to protect against subsequent modification.

    Parameters:
      `apdu` - the complete command APDU
    Throws:
      `NullPointerException` - if apdu is null
      `IllegalArgumentException` - if apdu does not contain a valid command APDU

  - ### CommandAPDU

    public CommandAPDU(byte[] apdu, int apduOffset, int apduLength)
    Constructs a CommandAPDU from a byte array containing the complete APDU contents (header and body). The APDU starts at the index `apduOffset` in the byte array and is `apduLength` bytes long.

    Note that the apdu bytes are copied to protect against subsequent modification.

    Parameters:
      `apdu` - the complete command APDU
      `apduOffset` - the offset in the byte array at which the apdu data begins
      `apduLength` - the length of the APDU
    Throws:
      `NullPointerException` - if apdu is null
      `IllegalArgumentException` - if apduOffset or apduLength are negative or if apduOffset + apduLength are greater than apdu.length, or if the specified bytes are not a valid APDU

  - ### CommandAPDU

    public CommandAPDU(ByteBuffer apdu)
    Creates a CommandAPDU from the ByteBuffer containing the complete APDU contents (header and body). The buffer's `position` must be set to the start of the APDU, its `limit` to the end of the APDU. Upon return, the buffer's `position` is equal to its limit; its limit remains unchanged.

    Note that the data in the ByteBuffer is copied to protect against subsequent modification.

    Parameters:
      `apdu` - the ByteBuffer containing the complete APDU
    Throws:
      `NullPointerException` - if apdu is null
      `IllegalArgumentException` - if apdu does not contain a valid command APDU

  - ### CommandAPDU

    public CommandAPDU(int cla, int ins, int p1, int p2)
    Constructs a CommandAPDU from the four header bytes. This is case 1 in ISO 7816, no command body.
    Parameters:
      `cla` - the class byte CLA
      `ins` - the instruction byte INS
      `p1` - the parameter byte P1
      `p2` - the parameter byte P2

  - ### CommandAPDU

    public CommandAPDU(int cla, int ins, int p1, int p2, int ne)
    Constructs a CommandAPDU from the four header bytes and the expected response data length. This is case 2 in ISO 7816, empty command data field with Ne specified. If Ne is 0, the APDU is encoded as ISO 7816 case 1.
    Parameters:
      `cla` - the class byte CLA
      `ins` - the instruction byte INS
      `p1` - the parameter byte P1
      `p2` - the parameter byte P2
      `ne` - the maximum number of expected data bytes in a response APDU
    Throws:
      `IllegalArgumentException` - if ne is negative or greater than 65536

  - ### CommandAPDU

    public CommandAPDU(int cla, int ins, int p1, int p2, byte[] data)
    Constructs a CommandAPDU from the four header bytes and command data. This is case 3 in ISO 7816, command data present and Ne absent. The value Nc is taken as data.length. If `data` is null or its length is 0, the APDU is encoded as ISO 7816 case 1.

    Note that the data bytes are copied to protect against subsequent modification.

    Parameters:
      `cla` - the class byte CLA
      `ins` - the instruction byte INS
      `p1` - the parameter byte P1
      `p2` - the parameter byte P2
      `data` - the byte array containing the data bytes of the command body
    Throws:
      `IllegalArgumentException` - if data.length is greater than 65535

  - ### CommandAPDU

    public CommandAPDU(int cla, int ins, int p1, int p2, byte[] data, int dataOffset, int dataLength)
    Constructs a CommandAPDU from the four header bytes and command data. This is case 3 in ISO 7816, command data present and Ne absent. The value Nc is taken as dataLength. If `dataLength` is 0, the APDU is encoded as ISO 7816 case 1.

    Note that the data bytes are copied to protect against subsequent modification.

    Parameters:
      `cla` - the class byte CLA
      `ins` - the instruction byte INS
      `p1` - the parameter byte P1
      `p2` - the parameter byte P2
      `data` - the byte array containing the data bytes of the command body
      `dataOffset` - the offset in the byte array at which the data bytes of the command body begin
      `dataLength` - the number of the data bytes in the command body
    Throws:
      `NullPointerException` - if data is null and dataLength is not 0
      `IllegalArgumentException` - if dataOffset or dataLength are negative or if dataOffset + dataLength are greater than data.length or if dataLength is greater than 65535

  - ### CommandAPDU

    public CommandAPDU(int cla, int ins, int p1, int p2, byte[] data, int ne)
    Constructs a CommandAPDU from the four header bytes, command data, and expected response data length. This is case 4 in ISO 7816, command data and Ne present. The value Nc is taken as data.length if `data` is non-null and as 0 otherwise. If Ne or Nc are zero, the APDU is encoded as case 1, 2, or 3 per ISO 7816.

    Note that the data bytes are copied to protect against subsequent modification.

    Parameters:
      `cla` - the class byte CLA
      `ins` - the instruction byte INS
      `p1` - the parameter byte P1
      `p2` - the parameter byte P2
      `data` - the byte array containing the data bytes of the command body
      `ne` - the maximum number of expected data bytes in a response APDU
    Throws:
      `IllegalArgumentException` - if data.length is greater than 65535 or if ne is negative or greater than 65536

  - ### CommandAPDU

    public CommandAPDU(int cla, int ins, int p1, int p2, byte[] data, int dataOffset, int dataLength, int ne)
    Constructs a CommandAPDU from the four header bytes, command data, and expected response data length. This is case 4 in ISO 7816, command data and Le present. The value Nc is taken as `dataLength`. If Ne or Nc are zero, the APDU is encoded as case 1, 2, or 3 per ISO 7816.

    Note that the data bytes are copied to protect against subsequent modification.

    Parameters:
      `cla` - the class byte CLA
      `ins` - the instruction byte INS
      `p1` - the parameter byte P1
      `p2` - the parameter byte P2
      `data` - the byte array containing the data bytes of the command body
      `dataOffset` - the offset in the byte array at which the data bytes of the command body begin
      `dataLength` - the number of the data bytes in the command body
      `ne` - the maximum number of expected data bytes in a response APDU
    Throws:
      `NullPointerException` - if data is null and dataLength is not 0
      `IllegalArgumentException` - if dataOffset or dataLength are negative or if dataOffset + dataLength are greater than data.length, or if ne is negative or greater than 65536, or if dataLength is greater than 65535

- ## Method Details

  - ### getCLA

    public int getCLA()
    Returns the value of the class byte CLA.
    Returns:
      the value of the class byte CLA.

  - ### getINS

    public int getINS()
    Returns the value of the instruction byte INS.
    Returns:
      the value of the instruction byte INS.

  - ### getP1

    public int getP1()
    Returns the value of the parameter byte P1.
    Returns:
      the value of the parameter byte P1.

  - ### getP2

    public int getP2()
    Returns the value of the parameter byte P2.
    Returns:
      the value of the parameter byte P2.

  - ### getNc

    public int getNc()
    Returns the number of data bytes in the command body (Nc) or 0 if this APDU has no body. This call is equivalent to `getData().length`.
    Returns:
      the number of data bytes in the command body or 0 if this APDU has no body.

  - ### getData

    public byte[] getData()
    Returns a copy of the data bytes in the command body. If this APDU as no body, this method returns a byte array with length zero.
    Returns:
      a copy of the data bytes in the command body or the empty byte array if this APDU has no body.

  - ### getNe

    public int getNe()
    Returns the maximum number of expected data bytes in a response APDU (Ne).
    Returns:
      the maximum number of expected data bytes in a response APDU.

  - ### getBytes

    public byte[] getBytes()
    Returns a copy of the bytes in this APDU.
    Returns:
      a copy of the bytes in this APDU.

  - ### toString

    public String toString()
    Returns a string representation of this command APDU.
    Overrides:
      `toString` in class `Object`
    Returns:
      a String representation of this command APDU.

  - ### equals

    public boolean equals(Object obj)
    Compares the specified object with this command APDU for equality. Returns true if the given object is also a CommandAPDU and its bytes are identical to the bytes in this CommandAPDU.
    Overrides:
      `equals` in class `Object`
    Parameters:
      `obj` - the object to be compared for equality with this command APDU
    Returns:
      true if the specified object is equal to this command APDU
    See Also:
      - `Object.hashCode()`
      - `HashMap`

  - ### hashCode

    public int hashCode()
    Returns the hash code value for this command APDU.
    Overrides:
      `hashCode` in class `Object`
    Returns:
      the hash code value for this command APDU.
    See Also:
      - `Object.equals(java.lang.Object)`
      - `System.identityHashCode(Object)`