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Oracle Coherence Community Edition
/*
* Copyright (c) 2000, 2020, Oracle and/or its affiliates.
*
* Licensed under the Universal Permissive License v 1.0 as shown at
* http://oss.oracle.com/licenses/upl.
*/
package com.tangosol.dev.assembler;
import java.io.IOException;
import java.io.DataInput;
import java.io.DataOutput;
/**
* Represent a Java Virtual Machine constant.
*
* @version 0.50, 05/12/98, assembler/dis-assembler
* @author Cameron Purdy
*/
public abstract class Constant extends VMStructure implements Constants, Comparable
{
// ----- constructors ---------------------------------------------------
/**
* Construct with a specific constant tag.
*
* @param nTag the constant tag
*/
protected Constant(int nTag)
{
m_nTag = nTag;
}
// ----- Constant operations --------------------------------------------
/**
* Based on the tag of the constant, which is encountered first in the
* stream, construct the correct constant class and disassemble it.
*
* @param stream the stream implementing java.io.DataInput from which
* to read the constant information
* @param pool the constant pool for the class which does not yet
* contain the constants referenced by this constant
*/
protected static Constant loadConstant(DataInput stream, ConstantPool pool)
throws IOException
{
int nTag = stream.readUnsignedByte();
Constant constant;
switch (nTag)
{
case CONSTANT_UTF8:
constant = new UtfConstant();
break;
case CONSTANT_INTEGER:
constant = new IntConstant();
break;
case CONSTANT_FLOAT:
constant = new FloatConstant();
break;
case CONSTANT_LONG:
constant = new LongConstant();
break;
case CONSTANT_DOUBLE:
constant = new DoubleConstant();
break;
case CONSTANT_CLASS:
constant = new ClassConstant();
break;
case CONSTANT_STRING:
constant = new StringConstant();
break;
case CONSTANT_FIELDREF:
constant = new FieldConstant();
break;
case CONSTANT_METHODREF:
constant = new MethodConstant();
break;
case CONSTANT_INTERFACEMETHODREF:
constant = new InterfaceConstant();
break;
case CONSTANT_NAMEANDTYPE:
constant = new SignatureConstant();
break;
case CONSTANT_METHODHANDLE:
ClassFile cf = pool.getClassFile();
constant = new MethodHandleConstant(
cf != null && cf.getMajorVersion() >= 52);
break;
case CONSTANT_METHODTYPE:
constant = new MethodTypeConstant();
break;
case CONSTANT_INVOKEDYNAMIC:
constant = new InvokeDynamicConstant();
break;
default:
throw new IOException("Invalid constant tag " + nTag);
}
constant.disassemble(stream, pool);
return constant;
}
/**
* Determine the enumerated JVM constant classification.
*
* @return the JVM constant tag
*/
public final int getTag()
{
return m_nTag;
}
/**
* Determine the number of constant pool slots used by the constant.
*
* @return the number of constant pool slots used by the constant
*/
protected final int getElementSize()
{
return CONSTANT_SIZE[m_nTag];
}
// ----- VMStructure operations -----------------------------------------
/**
* Read the constant information from the stream. Since constants can be
* inter-related, the dependencies are not derefenced until all constants
* are disassembled; at that point, the constants are resolved using the
* postdisassemble method.
*
* @param stream the stream implementing java.io.DataInput from which
* to read the constant information
* @param pool the constant pool for the class which does not yet
* contain the constants referenced by this constant
*/
protected abstract void disassemble(DataInput stream, ConstantPool pool)
throws IOException;
/**
* Resolve any referenced constants. When stored persistently, those
* constant types which refer to other constants do so by integer index;
* this method dereferences the integer index to access the referred-to
* constants directly. This method is overridden by constant types which
* reference other constants.
*
* @param pool the constant pool for the class which now contains all
* constants referenced by this constant
*/
protected void postdisassemble(ConstantPool pool)
{
}
/**
* Register any referenced constants. This method is overridden by
* constant types which reference other constants.
*
* The pre-assembly step collects the necessary entries for the constant
* pool. During this step, all constants used by this VM structure and
* any sub-structures are registered with (but not yet bound by position
* in) the constant pool.
*
* @param pool the constant pool for the class which needs to be
* populated with the constants required to build this
* VM structure
*/
protected void preassemble(ConstantPool pool)
{
}
/**
* The assembly process assembles and writes the constant to the passed
* output stream. The particular constant implementation should super
* to this generic implementation before assembling its own data.
*
* @param stream the stream implementing java.io.DataOutput to which to
* write the assembled constant
* @param pool the constant pool for the class which by this point
* contains the entire set of constants required to build
* this VM structure
*/
protected void assemble(DataOutput stream, ConstantPool pool)
throws IOException
{
stream.writeByte(m_nTag);
}
// ----- Comparable operations ------------------------------------------
/**
* Compares this Object with the specified Object for order. Returns a
* negative integer, zero, or a positive integer as this Object is less
* than, equal to, or greater than the given Object.
*
* @param obj the Object to be compared.
*
* @return a negative integer, zero, or a positive integer as this Object
* is less than, equal to, or greater than the given Object.
*
* @exception ClassCastException the specified Object's type prevents it
* from being compared to this Object.
*/
public abstract int compareTo(Object obj);
// ----- Object operations ----------------------------------------------
/**
* Produce a human-readable string describing the constant.
*
* @return a string describing the constant
*/
public abstract String toString();
/**
* Format the constant as it would appear in JASM code.
*
* @return the constant as it would appear in JASM code
*/
public abstract String format();
/**
* Compare this object to another object for equality.
*
* @param obj the other object to compare to this
*
* @return true if this object equals that object
*/
public abstract boolean equals(Object obj);
// ----- data members ---------------------------------------------------
/**
* The name of this class.
*/
private static final String CLASS = "Constant";
/**
* The JVM constant classification tag.
*/
private int m_nTag;
/**
* The cached location of the constant in the pool; used as an
* optimization to avoid repeatedly searching for the same constant if
* it isn't actually moving around in the pool.
*/
protected transient int m_iLastKnownLocation;
}