    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 *  Unless required by applicable law or agreed to in writing, software
    012 *  distributed under the License is distributed on an "AS IS" BASIS,
    013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 *  See the License for the specific language governing permissions and
    015 *  limitations under the License.
    016 */
    017package org.apache.bcel.classfile;
    018
    019import java.io.DataInput;
    020import java.io.DataOutputStream;
    021import java.io.IOException;
    022
    023import org.apache.bcel.Const;
    024import org.apache.bcel.util.Args;
    025
    026/**
    027 * This class is derived from <em>Attribute</em> and represents a constant value, i.e., a default value for initializing
    028 * a class field. This class is instantiated by the <em>Attribute.readAttribute()</em> method.
    029 *
    030 * <pre>
    031 * ConstantValue_attribute {
    032 *   u2 attribute_name_index;
    033 *   u4 attribute_length;
    034 *   u2 constantvalue_index;
    035 * }
    036 * </pre>
    037 * @see Attribute
    038 */
    039public final class ConstantValue extends Attribute {
    040
    041    private int constantValueIndex;
    042
    043    /**
    044     * Initialize from another object. Note that both objects use the same references (shallow copy). Use clone() for a
    045     * physical copy.
    046     *
    047     * @param c Source to copy.
    048     */
    049    public ConstantValue(final ConstantValue c) {
    050        this(c.getNameIndex(), c.getLength(), c.getConstantValueIndex(), c.getConstantPool());
    051    }
    052
    053    /**
    054     * Constructs object from input stream.
    055     *
    056     * @param nameIndex Name index in constant pool
    057     * @param length Content length in bytes
    058     * @param input Input stream
    059     * @param constantPool Array of constants
    060     * @throws IOException if an I/O error occurs.
    061     */
    062    ConstantValue(final int nameIndex, final int length, final DataInput input, final ConstantPool constantPool) throws IOException {
    063        this(nameIndex, length, input.readUnsignedShort(), constantPool);
    064    }
    065
    066    /**
    067     * @param nameIndex Name index in constant pool
    068     * @param length Content length in bytes
    069     * @param constantValueIndex Index in constant pool
    070     * @param constantPool Array of constants
    071     */
    072    public ConstantValue(final int nameIndex, final int length, final int constantValueIndex, final ConstantPool constantPool) {
    073        super(Const.ATTR_CONSTANT_VALUE, nameIndex, Args.require(length, 2, "ConstantValue attribute length"), constantPool);
    074        this.constantValueIndex = constantValueIndex;
    075    }
    076
    077    /**
    078     * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
    079     * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
    080     *
    081     * @param v Visitor object
    082     */
    083    @Override
    084    public void accept(final Visitor v) {
    085        v.visitConstantValue(this);
    086    }
    087
    088    /**
    089     * @return deep copy of this attribute
    090     */
    091    @Override
    092    public Attribute copy(final ConstantPool constantPool) {
    093        final ConstantValue c = (ConstantValue) clone();
    094        c.setConstantPool(constantPool);
    095        return c;
    096    }
    097
    098    /**
    099     * Dump constant value attribute to file stream on binary format.
    100     *
    101     * @param file Output file stream
    102     * @throws IOException if an I/O error occurs.
    103     */
    104    @Override
    105    public void dump(final DataOutputStream file) throws IOException {
    106        super.dump(file);
    107        file.writeShort(constantValueIndex);
    108    }
    109
    110    /**
    111     * @return Index in constant pool of constant value.
    112     */
    113    public int getConstantValueIndex() {
    114        return constantValueIndex;
    115    }
    116
    117    /**
    118     * @param constantValueIndex the index info the constant pool of this constant value
    119     */
    120    public void setConstantValueIndex(final int constantValueIndex) {
    121        this.constantValueIndex = constantValueIndex;
    122    }
    123
    124    /**
    125     * @return String representation of constant value.
    126     */
    127    @Override
    128    public String toString() {
    129        Constant c = super.getConstantPool().getConstant(constantValueIndex);
    130        String buf;
    131        int i;
    132        // Print constant to string depending on its type
    133        switch (c.getTag()) {
    134        case Const.CONSTANT_Long:
    135            buf = String.valueOf(((ConstantLong) c).getBytes());
    136            break;
    137        case Const.CONSTANT_Float:
    138            buf = String.valueOf(((ConstantFloat) c).getBytes());
    139            break;
    140        case Const.CONSTANT_Double:
    141            buf = String.valueOf(((ConstantDouble) c).getBytes());
    142            break;
    143        case Const.CONSTANT_Integer:
    144            buf = String.valueOf(((ConstantInteger) c).getBytes());
    145            break;
    146        case Const.CONSTANT_String:
    147            i = ((ConstantString) c).getStringIndex();
    148            c = super.getConstantPool().getConstantUtf8(i);
    149            buf = "\"" + Utility.convertString(((ConstantUtf8) c).getBytes()) + "\"";
    150            break;
    151        default:
    152            throw new IllegalStateException("Type of ConstValue invalid: " + c);
    153        }
    154        return buf;
    155    }
    156}