org.apache.bcel.classfile

## Class ConstantPool

- java.lang.Object
- - org.apache.bcel.classfile.ConstantPool

- All Implemented Interfaces:
    Cloneable, Iterable<Constant>, Node

      public class ConstantPool
      extends Object
      implements Cloneable, Node, Iterable<Constant>

  This class represents the constant pool, i.e., a table of constants, of a parsed classfile. It may contain null references, due to the JVM specification that skips an entry after an 8-byte constant (double, long) entry. Those interested in generating constant pools programmatically should see ConstantPoolGen.
  See Also:
    `Constant`, `ConstantPoolGen`

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `ConstantPool(Constant[] constantPool)`
    `ConstantPool(DataInput input)` Reads constants from given input stream.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `accept(Visitor v)` Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
    `String` | `constantToString(Constant c)` Resolves constant to a string representation.
    `String` | `constantToString(int index, byte tag)` Retrieves constant at `index' from constant pool and resolve it to a string representation.
    `ConstantPool` | `copy()`
    `void` | `dump(DataOutputStream file)` Dump constant pool to file stream in binary format.
    `<T extends Constant> T` | `getConstant(int index)` Gets constant from constant pool.
    `<T extends Constant> T` | `getConstant(int index, byte tag)` Gets constant from constant pool and check whether it has the expected type.
    `<T extends Constant> T` | `getConstant(int index, byte tag, Class<T> castTo)` Gets constant from constant pool and check whether it has the expected type.
    `<T extends Constant> T` | `getConstant(int index, Class<T> castTo)` Gets constant from constant pool.
    `ConstantInteger` | `getConstantInteger(int index)` Gets constant from constant pool and check whether it has the expected type.
    `Constant[]` | `getConstantPool()`
    `String` | `getConstantString(int index, byte tag)` Gets string from constant pool and bypass the indirection of `ConstantClass' and `ConstantString' objects.
    `ConstantUtf8` | `getConstantUtf8(int index)` Gets constant from constant pool and check whether it has the expected type.
    `int` | `getLength()`
    `Iterator<Constant>` | `iterator()`
    `void` | `setConstant(int index, Constant constant)`
    `void` | `setConstantPool(Constant[] constantPool)`
    `String` | `toString()`

    - ### Methods inherited from class java.lang.Object

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

    - ### Methods inherited from interface java.lang.Iterable

      `forEach, spliterator`

- - ### Constructor Detail

    - #### ConstantPool

          public ConstantPool(Constant[] constantPool)

      Parameters:
        `constantPool` - Array of constants

    - #### ConstantPool

          public ConstantPool(DataInput input)
                       throws IOException

      Reads constants from given input stream.
      Parameters:
        `input` - Input stream
      Throws:
        `IOException` - if problem in readUnsignedShort or readConstant

  - ### Method Detail

    - #### accept

          public void accept(Visitor v)

      Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class. I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
      Specified by:
        `accept` in interface `Node`
      Parameters:
        `v` - Visitor object

    - #### constantToString

          public String constantToString(Constant c)
                                  throws IllegalArgumentException

      Resolves constant to a string representation.
      Parameters:
        `c` - Constant to be printed
      Returns:
        String representation
      Throws:
        `IllegalArgumentException` - if c is unknown constant type

    - #### constantToString

          public String constantToString(int index,
                                         byte tag)

      Retrieves constant at `index' from constant pool and resolve it to a string representation.
      Parameters:
        `index` - of constant in constant pool
        `tag` - expected type
      Returns:
        String representation

    - #### copy

          public ConstantPool copy()

      Returns:
        deep copy of this constant pool

    - #### dump

          public void dump(DataOutputStream file)
                    throws IOException

      Dump constant pool to file stream in binary format.
      Parameters:
        `file` - Output file stream
      Throws:
        `IOException` - if problem in writeShort or dump

    - #### getConstant

          public <T extends Constant> T getConstant(int index)
                                             throws ClassFormatException

      Gets constant from constant pool.
      Parameters:
        `index` - Index in constant pool
      Returns:
        Constant value
      Throws:
        `ClassFormatException` - if index is invalid
      See Also:
        `Constant`

    - #### getConstant

          public <T extends Constant> T getConstant(int index,
                                                    byte tag)
                                             throws ClassFormatException

      Gets constant from constant pool and check whether it has the expected type.
      Parameters:
        `index` - Index in constant pool
        `tag` - Tag of expected constant, i.e., its type
      Returns:
        Constant value
      Throws:
        `ClassFormatException` - if constant type does not match tag
      See Also:
        `Constant`

    - #### getConstant

          public <T extends Constant> T getConstant(int index,
                                                    byte tag,
                                                    Class<T> castTo)
                                             throws ClassFormatException

      Gets constant from constant pool and check whether it has the expected type.
      Parameters:
        `index` - Index in constant pool
        `tag` - Tag of expected constant, i.e., its type
      Returns:
        Constant value
      Throws:
        `ClassFormatException` - if constant type does not match tag
      Since:
        6.6.0
      See Also:
        `Constant`

    - #### getConstant

          public <T extends Constant> T getConstant(int index,
                                                    Class<T> castTo)
                                             throws ClassFormatException

      Gets constant from constant pool.
      Type Parameters:
        `T` - A `Constant` subclass
      Parameters:
        `index` - Index in constant pool
        `castTo` - The `Constant` subclass to cast to.
      Returns:
        Constant value
      Throws:
        `ClassFormatException` - if index is invalid
      Since:
        6.6.0
      See Also:
        `Constant`

    - #### getConstantInteger

          public ConstantInteger getConstantInteger(int index)

      Gets constant from constant pool and check whether it has the expected type.
      Parameters:
        `index` - Index in constant pool
      Returns:
        ConstantInteger value
      Throws:
        `ClassFormatException` - if constant type does not match tag
      See Also:
        `ConstantInteger`

    - #### getConstantPool

          public Constant[] getConstantPool()

      Returns:
        Array of constants.
      See Also:
        `Constant`

    - #### getConstantString

          public String getConstantString(int index,
                                          byte tag)
                                   throws IllegalArgumentException

      Gets string from constant pool and bypass the indirection of `ConstantClass' and `ConstantString' objects. I.e. these classes have an index field that points to another entry of the constant pool of type `ConstantUtf8' which contains the real data.
      Parameters:
        `index` - Index in constant pool
        `tag` - Tag of expected constant, either ConstantClass or ConstantString
      Returns:
        Contents of string reference
      Throws:
        `IllegalArgumentException` - if tag is invalid
      See Also:
        `ConstantClass`, `ConstantString`

    - #### getConstantUtf8

          public ConstantUtf8 getConstantUtf8(int index)
                                       throws ClassFormatException

      Gets constant from constant pool and check whether it has the expected type.
      Parameters:
        `index` - Index in constant pool
      Returns:
        ConstantUtf8 value
      Throws:
        `ClassFormatException` - if constant type does not match tag
      See Also:
        `ConstantUtf8`

    - #### getLength

          public int getLength()

      Returns:
        Length of constant pool.

    - #### iterator

          public Iterator<Constant> iterator()

      Specified by:
        `iterator` in interface `Iterable<Constant>`

    - #### setConstant

          public void setConstant(int index,
                                  Constant constant)

      Parameters:
        `constant` - Constant to set

    - #### setConstantPool

          public void setConstantPool(Constant[] constantPool)

      Parameters:
        `constantPool` -

    - #### toString

          public String toString()

      Overrides:
        `toString` in class `Object`
      Returns:
        String representation.

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