ConstantValue.java :  » Scripting » bcel-5.2 » org » apache » bcel » classfile » Java Open Source

/*
 * Copyright  2000-2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); 
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License. 
 *
 */
package org.apache.bcel.classfile;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import org.apache.bcel.Constants;

/**
 * This class is derived from <em>Attribute</em> and represents a constant 
 * value, i.e., a default value for initializing a class field.
 * This class is instantiated by the <em>Attribute.readAttribute()</em> method.
 *
 * @version $Id: ConstantValue.java 386056 2006-03-15 11:31:56Z tcurdt $
 * @author  <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
 * @see     Attribute
 */
public final class ConstantValue extends Attribute {

    private int constantvalue_index;


    /**
     * Initialize from another object. Note that both objects use the same
     * references (shallow copy). Use clone() for a physical copy.
     */
    public ConstantValue(ConstantValue c) {
        this(c.getNameIndex(), c.getLength(), c.getConstantValueIndex(), c.getConstantPool());
    }


    /**
     * Construct object from file stream.
     * @param name_index Name index in constant pool
     * @param length Content length in bytes
     * @param file Input stream
     * @param constant_pool Array of constants
     * @throws IOException
     */
    ConstantValue(int name_index, int length, DataInputStream file, ConstantPool constant_pool)
            throws IOException {
        this(name_index, length, file.readUnsignedShort(), constant_pool);
    }


    /**
     * @param name_index Name index in constant pool
     * @param length Content length in bytes
     * @param constantvalue_index Index in constant pool
     * @param constant_pool Array of constants
     */
    public ConstantValue(int name_index, int length, int constantvalue_index,
            ConstantPool constant_pool) {
        super(Constants.ATTR_CONSTANT_VALUE, name_index, length, constant_pool);
        this.constantvalue_index = constantvalue_index;
    }


    /**
     * Called by objects that are traversing the nodes of the tree implicitely
     * defined by the contents of a Java class. I.e., the hierarchy of methods,
     * fields, attributes, etc. spawns a tree of objects.
     *
     * @param v Visitor object
     */
    public void accept( Visitor v ) {
        v.visitConstantValue(this);
    }


    /**
     * Dump constant value attribute to file stream on binary format.
     *
     * @param file Output file stream
     * @throws IOException
     */
    public final void dump( DataOutputStream file ) throws IOException {
        super.dump(file);
        file.writeShort(constantvalue_index);
    }


    /**
     * @return Index in constant pool of constant value.
     */
    public final int getConstantValueIndex() {
        return constantvalue_index;
    }


    /**
     * @param constantvalue_index the index info the constant pool of this constant value
     */
    public final void setConstantValueIndex( int constantvalue_index ) {
        this.constantvalue_index = constantvalue_index;
    }


    /**
     * @return String representation of constant value.
     */
    public final String toString() {
        Constant c = constant_pool.getConstant(constantvalue_index);
        String buf;
        int i;
        // Print constant to string depending on its type
        switch (c.getTag()) {
            case Constants.CONSTANT_Long:
                buf = "" + ((ConstantLong) c).getBytes();
                break;
            case Constants.CONSTANT_Float:
                buf = "" + ((ConstantFloat) c).getBytes();
                break;
            case Constants.CONSTANT_Double:
                buf = "" + ((ConstantDouble) c).getBytes();
                break;
            case Constants.CONSTANT_Integer:
                buf = "" + ((ConstantInteger) c).getBytes();
                break;
            case Constants.CONSTANT_String:
                i = ((ConstantString) c).getStringIndex();
                c = constant_pool.getConstant(i, Constants.CONSTANT_Utf8);
                buf = "\"" + Utility.convertString(((ConstantUtf8) c).getBytes()) + "\"";
                break;
            default:
                throw new IllegalStateException("Type of ConstValue invalid: " + c);
        }
        return buf;
    }


    /**
     * @return deep copy of this attribute
     */
    public Attribute copy( ConstantPool _constant_pool ) {
        ConstantValue c = (ConstantValue) clone();
        c.constant_pool = _constant_pool;
        return c;
    }
}