//  Constant.java -- values from a Java classfile "constant" tablepackage toba.classfile;import java.io.*;import java.util.*;public class Constant {		// constant table entry    public int index;		// entry index    public int tag;		// constant type    public Object value;	// resolved constant value// tag typespublic static final int CLASS		=  7;public static final int FIELD		=  9;public static final int METHOD		= 10;public static final int INTERFACE	= 11;public static final int STRING		=  8;public static final int INTEGER		=  3;public static final int FLOAT		=  4;public static final int LONG		=  5;public static final int DOUBLE		=  6;public static final int NAMETYPE	= 12;public static final int UTF8		=  1;public static final int UNICODE		=  2;private static final String TagToName [] = new String [13];static {  TagToName [CLASS] = "CLASS";  TagToName [FIELD] = "FIELD";  TagToName [METHOD] = "METHOD";  TagToName [INTERFACE] = "INTERFACE";  TagToName [STRING] = "STRING";  TagToName [INTEGER] = "INTEGER";  TagToName [FLOAT] = "FLOAT";  TagToName [LONG] = "LONG";  TagToName [DOUBLE] = "DOUBLE";  TagToName [NAMETYPE] = "NAMETYPE";  TagToName [UTF8] = "UTF8";  TagToName [UNICODE] = "UNICODE";}/** This is like java.io.DataInputStream.readUTF, except it doesn't fall  * through to the error case on three-byte UTF codes.  That bug was  * fixed in jdk1.1.1.   * @return the String.  */private final static String readUTF(DataInput in) throws IOException {        int utflen = in.readUnsignedShort();        char str[] = new char[utflen];	int count = 0;	int strlen = 0;	while (count < utflen) {	    int c = in.readUnsignedByte();	    int char2, char3;	    switch (c >> 4) { 	        case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:		    // 0xxxxxxx		    count++;		    str[strlen++] = (char)c;		    break;	        case 12: case 13:		    // 110x xxxx   10xx xxxx		    count += 2;		    if (count > utflen) 			throw new UTFDataFormatException();		  		    char2 = in.readUnsignedByte();		    if ((char2 & 0xC0) != 0x80)			throw new UTFDataFormatException();		  		    str[strlen++] = (char)(((c & 0x1F) << 6) | (char2 & 0x3F));		    break;	        case 14:		    // 1110 xxxx  10xx xxxx  10xx xxxx		    count += 3;		    if (count > utflen) 			throw new UTFDataFormatException();		  		    char2 = in.readUnsignedByte();		    char3 = in.readUnsignedByte();		    if (((char2 & 0xC0) != 0x80) || ((char3 & 0xC0) != 0x80))			throw new UTFDataFormatException();		  		    str[strlen++] = (char)(((c & 0x0F) << 12) |					   ((char2 & 0x3F) << 6) |					   ((char3 & 0x3F) << 0));                    break; // DON'T FALL THROUGH	        default:		    // 10xx xxxx,  1111 xxxx		    throw new UTFDataFormatException();		  		}	}        return new String(str, 0, strlen);    }//  load(d) -- read and crack constant table from stream d.static Constant[] load (DataInputStream d)    throws ClassFormatError, IOException{    // allocate constant table; first entry is unused    Constant[] table = new Constant[d.readUnsignedShort()];    table[0] = null;    // read constant table entries    for (int i = 1; i < table.length; i++) {	Constant c = new Constant();	table[i] = c;	c.index = i;	c.tag = d.readByte();	switch (c.tag) {	    case UTF8:		c.value = readUTF(d).intern(); // intern strings as they come in		break;	    case UNICODE:		int len = d.readUnsignedShort();		char s[] = new char[len];		for (int j = 0; j < len; j++)		    s[j] = (char)d.readUnsignedShort();		c.value = new String(s).intern(); // intern strings as they come in		break;	    case INTEGER:		c.value = new Integer(d.readInt());		break;	    case FLOAT:		c.value = new Float(d.readFloat());		break;	    case LONG:		c.value = new Long(d.readLong());		table[++i] = null;	// following entry unused		break;	    case DOUBLE:		c.value = new Double(d.readDouble());		table[++i] = null;	// following entry unused		break;	    case CLASS:	    case STRING:		c.value = new Integer(d.readUnsignedShort());		break;	    case FIELD:	    case METHOD:	    case INTERFACE:	    case NAMETYPE:		Pair p = new Pair();		p.i1 = d.readUnsignedShort();		p.i2 = d.readUnsignedShort();		c.value = p;		break;	    default:		throw new ClassFormatError(		    "unrecognized constant tag " + c.tag);	}    }    // Now we need to patch up references between constant table    // entries to a useable form.    // first, replace strings with actual strings, not ints    for (int i = 1; i < table.length; i++) {	Constant c = table[i];	if ((c != null) && (c.tag == STRING)) {	    Constant c2 = table[((Integer)c.value).intValue()];	    if ((c2.tag != UTF8) && (c2.tag != UNICODE))		throw new 		    ClassFormatError("Invalid string in constant pool (" 				     + i + ")");	    c.value = c2.value;	}    }    // next, replace classes with ClassRefs    for (int i = 1; i < table.length; i++) {	Constant c = table[i];	if ((c != null) && (c.tag == CLASS)) {	    String s = (String)table[((Integer)c.value).intValue()].value;	    c.value = ClassRef.byName (s.replace('/', '.'));	}    }    // then, fill in fields of reference entries    for (int i = 1; i < table.length; i++) {	Constant c = table[i];	Pair p, p2;	if (c != null) switch (c.tag) {	    case FIELD:	    case METHOD:	    case INTERFACE:		p = (Pair)c.value;		p2 = (Pair)table[p.i2].value;		ClassRef cref = (ClassRef)table[p.i1].value;		String name = (String)table[p2.i1].value;		String sig = (String)table[p2.i2].value;		if (c.tag == FIELD)		    c.value = new VariableRef(cref, name, sig);		else if (c.tag == METHOD)		    c.value = new MethodRef(cref, name, sig);		else if (c.tag == INTERFACE)		    c.value = new InterfaceRef(cref, name, sig);		break;	}    }    return table;}public StringtoString (){    return TagToName [tag] + "/" + value;}//  dump(d, table) -- dump a constant tablepublic static void dump(PrintWriter d, Constant table[]){    d.println();    d.println("/*  Constant table:");    for (int i = 1; i < table.length; i++) {	Constant c = table[i];	if (c == null)				// if unused entry	    continue;	d.print("    c" + i + ".  (" + c.tag + ")  ");	d.println(c.value);    }    d.println("*/");    d.println();}} // class Constant