    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one
    003 * or more contributor license agreements.  See the NOTICE file
    004 * distributed with this work for additional information
    005 * regarding copyright ownership.  The ASF licenses this file
    006 * to you under the Apache License, Version 2.0 (the
    007 * "License"); you may not use this file except in compliance
    008 * with the License.  You may obtain a copy of the License at
    009 *
    010 *   https://www.apache.org/licenses/LICENSE-2.0
    011 *
    012 * Unless required by applicable law or agreed to in writing,
    013 * software distributed under the License is distributed on an
    014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    015 * KIND, either express or implied.  See the License for the
    016 * specific language governing permissions and limitations
    017 * under the License.
    018 */
    019package org.apache.bcel.classfile;
    020
    021import java.io.DataInput;
    022import java.io.DataOutputStream;
    023import java.io.IOException;
    024
    025import org.apache.bcel.Const;
    026import org.apache.bcel.util.Args;
    027
    028/**
    029 * This class is derived from <em>Attribute</em> and represents a constant value, that is, a default value for initializing
    030 * a class field. This class is instantiated by the <em>Attribute.readAttribute()</em> method.
    031 *
    032 * <pre>
    033 * ConstantValue_attribute {
    034 *   u2 attribute_name_index;
    035 *   u4 attribute_length;
    036 *   u2 constantvalue_index;
    037 * }
    038 * </pre>
    039 *
    040 * @see Attribute
    041 */
    042public final class ConstantValue extends Attribute {
    043
    044    private int constantValueIndex;
    045
    046    /**
    047     * Initialize from another object. Note that both objects use the same references (shallow copy). Use clone() for a
    048     * physical copy.
    049     *
    050     * @param c Source to copy.
    051     */
    052    public ConstantValue(final ConstantValue c) {
    053        this(c.getNameIndex(), c.getLength(), c.getConstantValueIndex(), c.getConstantPool());
    054    }
    055
    056    /**
    057     * Constructs object from input stream.
    058     *
    059     * @param nameIndex Name index in constant pool.
    060     * @param length Content length in bytes.
    061     * @param input Input stream.
    062     * @param constantPool Array of constants.
    063     * @throws IOException if an I/O error occurs.
    064     */
    065    ConstantValue(final int nameIndex, final int length, final DataInput input, final ConstantPool constantPool) throws IOException {
    066        this(nameIndex, length, input.readUnsignedShort(), constantPool);
    067    }
    068
    069    /**
    070     * Constructs a ConstantValue.
    071     *
    072     * @param nameIndex Name index in constant pool.
    073     * @param length Content length in bytes.
    074     * @param constantValueIndex Index in constant pool.
    075     * @param constantPool Array of constants.
    076     */
    077    public ConstantValue(final int nameIndex, final int length, final int constantValueIndex, final ConstantPool constantPool) {
    078        super(Const.ATTR_CONSTANT_VALUE, nameIndex, Args.require(length, 2, "ConstantValue attribute length"), constantPool);
    079        this.constantValueIndex = constantValueIndex;
    080    }
    081
    082    /**
    083     * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
    084     * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
    085     *
    086     * @param v Visitor object.
    087     */
    088    @Override
    089    public void accept(final Visitor v) {
    090        v.visitConstantValue(this);
    091    }
    092
    093    /**
    094     * Creates a deep copy of this attribute.
    095     *
    096     * @param constantPool the constant pool.
    097     * @return deep copy of this attribute.
    098     */
    099    @Override
    100    public Attribute copy(final ConstantPool constantPool) {
    101        final ConstantValue c = (ConstantValue) clone();
    102        c.setConstantPool(constantPool);
    103        return c;
    104    }
    105
    106    /**
    107     * Dumps constant value attribute to file stream on binary format.
    108     *
    109     * @param file Output file stream.
    110     * @throws IOException if an I/O error occurs.
    111     */
    112    @Override
    113    public void dump(final DataOutputStream file) throws IOException {
    114        super.dump(file);
    115        file.writeShort(constantValueIndex);
    116    }
    117
    118    /**
    119     * Gets the index in constant pool of constant value.
    120     *
    121     * @return Index in constant pool of constant value.
    122     */
    123    public int getConstantValueIndex() {
    124        return constantValueIndex;
    125    }
    126
    127    /**
    128     * Sets the constant value index.
    129     *
    130     * @param constantValueIndex the index info the constant pool of this constant value.
    131     */
    132    public void setConstantValueIndex(final int constantValueIndex) {
    133        this.constantValueIndex = constantValueIndex;
    134    }
    135
    136    /**
    137     * @return String representation of constant value.
    138     */
    139    @Override
    140    public String toString() {
    141        Constant c = super.getConstantPool().getConstant(constantValueIndex);
    142        final String buf;
    143        final int i;
    144        // Print constant to string depending on its type
    145        switch (c.getTag()) {
    146        case Const.CONSTANT_Long:
    147            buf = String.valueOf(((ConstantLong) c).getBytes());
    148            break;
    149        case Const.CONSTANT_Float:
    150            buf = String.valueOf(((ConstantFloat) c).getBytes());
    151            break;
    152        case Const.CONSTANT_Double:
    153            buf = String.valueOf(((ConstantDouble) c).getBytes());
    154            break;
    155        case Const.CONSTANT_Integer:
    156            buf = String.valueOf(((ConstantInteger) c).getBytes());
    157            break;
    158        case Const.CONSTANT_String:
    159            i = ((ConstantString) c).getStringIndex();
    160            c = super.getConstantPool().getConstantUtf8(i);
    161            buf = "\"" + Utility.convertString(((ConstantUtf8) c).getBytes()) + "\"";
    162            break;
    163        default:
    164            throw new IllegalStateException("Type of ConstValue invalid: " + c);
    165        }
    166        return buf;
    167    }
    168}