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, i.e., 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 * @see Attribute
040 */
041public final class ConstantValue extends Attribute {
042
043    private int constantValueIndex;
044
045    /**
046     * Initialize from another object. Note that both objects use the same references (shallow copy). Use clone() for a
047     * physical copy.
048     *
049     * @param c Source to copy.
050     */
051    public ConstantValue(final ConstantValue c) {
052        this(c.getNameIndex(), c.getLength(), c.getConstantValueIndex(), c.getConstantPool());
053    }
054
055    /**
056     * Constructs object from input stream.
057     *
058     * @param nameIndex Name index in constant pool
059     * @param length Content length in bytes
060     * @param input Input stream
061     * @param constantPool Array of constants
062     * @throws IOException if an I/O error occurs.
063     */
064    ConstantValue(final int nameIndex, final int length, final DataInput input, final ConstantPool constantPool) throws IOException {
065        this(nameIndex, length, input.readUnsignedShort(), constantPool);
066    }
067
068    /**
069     * @param nameIndex Name index in constant pool
070     * @param length Content length in bytes
071     * @param constantValueIndex Index in constant pool
072     * @param constantPool Array of constants
073     */
074    public ConstantValue(final int nameIndex, final int length, final int constantValueIndex, final ConstantPool constantPool) {
075        super(Const.ATTR_CONSTANT_VALUE, nameIndex, Args.require(length, 2, "ConstantValue attribute length"), constantPool);
076        this.constantValueIndex = constantValueIndex;
077    }
078
079    /**
080     * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
081     * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
082     *
083     * @param v Visitor object
084     */
085    @Override
086    public void accept(final Visitor v) {
087        v.visitConstantValue(this);
088    }
089
090    /**
091     * @return deep copy of this attribute
092     */
093    @Override
094    public Attribute copy(final ConstantPool constantPool) {
095        final ConstantValue c = (ConstantValue) clone();
096        c.setConstantPool(constantPool);
097        return c;
098    }
099
100    /**
101     * Dump constant value attribute to file stream on binary format.
102     *
103     * @param file Output file stream
104     * @throws IOException if an I/O error occurs.
105     */
106    @Override
107    public void dump(final DataOutputStream file) throws IOException {
108        super.dump(file);
109        file.writeShort(constantValueIndex);
110    }
111
112    /**
113     * @return Index in constant pool of constant value.
114     */
115    public int getConstantValueIndex() {
116        return constantValueIndex;
117    }
118
119    /**
120     * @param constantValueIndex the index info the constant pool of this constant value
121     */
122    public void setConstantValueIndex(final int constantValueIndex) {
123        this.constantValueIndex = constantValueIndex;
124    }
125
126    /**
127     * @return String representation of constant value.
128     */
129    @Override
130    public String toString() {
131        Constant c = super.getConstantPool().getConstant(constantValueIndex);
132        final String buf;
133        final int i;
134        // Print constant to string depending on its type
135        switch (c.getTag()) {
136        case Const.CONSTANT_Long:
137            buf = String.valueOf(((ConstantLong) c).getBytes());
138            break;
139        case Const.CONSTANT_Float:
140            buf = String.valueOf(((ConstantFloat) c).getBytes());
141            break;
142        case Const.CONSTANT_Double:
143            buf = String.valueOf(((ConstantDouble) c).getBytes());
144            break;
145        case Const.CONSTANT_Integer:
146            buf = String.valueOf(((ConstantInteger) c).getBytes());
147            break;
148        case Const.CONSTANT_String:
149            i = ((ConstantString) c).getStringIndex();
150            c = super.getConstantPool().getConstantUtf8(i);
151            buf = "\"" + Utility.convertString(((ConstantUtf8) c).getBytes()) + "\"";
152            break;
153        default:
154            throw new IllegalStateException("Type of ConstValue invalid: " + c);
155        }
156        return buf;
157    }
158}