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;
024
025/**
026 * This class is derived from the abstract {@link Constant} and represents a reference to a (external) class.
027 *
028 * @see Constant
029 */
030public final class ConstantClass extends Constant implements ConstantObject {
031
032    private int nameIndex; // Identical to ConstantString except for the name
033
034    /**
035     * Initialize from another object.
036     */
037    public ConstantClass(final ConstantClass c) {
038        this(c.getNameIndex());
039    }
040
041    /**
042     * Constructs an instance from file data.
043     *
044     * @param dataInput Input stream
045     * @throws IOException if an I/O error occurs reading from the given {@code dataInput}.
046     */
047    ConstantClass(final DataInput dataInput) throws IOException {
048        this(dataInput.readUnsignedShort());
049    }
050
051    /**
052     * @param nameIndex Name index in constant pool. Should refer to a ConstantUtf8.
053     */
054    public ConstantClass(final int nameIndex) {
055        super(Const.CONSTANT_Class);
056        this.nameIndex = nameIndex;
057    }
058
059    /**
060     * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
061     * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
062     *
063     * @param v Visitor object
064     */
065    @Override
066    public void accept(final Visitor v) {
067        v.visitConstantClass(this);
068    }
069
070    /**
071     * Dumps constant class to file stream in binary format.
072     *
073     * @param file Output file stream
074     * @throws IOException if an I/O error occurs writing to the DataOutputStream.
075     */
076    @Override
077    public void dump(final DataOutputStream file) throws IOException {
078        file.writeByte(super.getTag());
079        file.writeShort(nameIndex);
080    }
081
082    /**
083     * @return dereferenced string
084     */
085    public String getBytes(final ConstantPool cp) {
086        return (String) getConstantValue(cp);
087    }
088
089    /**
090     * @return String object
091     */
092    @Override
093    public Object getConstantValue(final ConstantPool cp) {
094        return cp.getConstantUtf8(nameIndex).getBytes();
095    }
096
097    /**
098     * @return Name index in constant pool of class name.
099     */
100    public int getNameIndex() {
101        return nameIndex;
102    }
103
104    /**
105     * @param nameIndex the name index in the constant pool of this Constant Class
106     */
107    public void setNameIndex(final int nameIndex) {
108        this.nameIndex = nameIndex;
109    }
110
111    /**
112     * @return String representation.
113     */
114    @Override
115    public String toString() {
116        return super.toString() + "(nameIndex = " + nameIndex + ")";
117    }
118}