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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.tomcat.util.bcel.classfile;
import java.io.DataInput;
import java.io.IOException;
import org.apache.tomcat.util.bcel.Constants;
/**
* This class represents the constant pool, i.e., a table of constants, of
* a parsed classfile. It may contain null references, due to the JVM
* specification that skips an entry after an 8-byte constant (double,
* long) entry. Those interested in generating constant pools
* programatically should see <a href="../generic/ConstantPoolGen.html">
* ConstantPoolGen</a>.
* @see Constant
* @author <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
*/
public class ConstantPool {
private final Constant[] constant_pool;
/**
* Read constants from given file stream.
*
* @param file Input stream
* @throws IOException
* @throws ClassFormatException
*/
ConstantPool(DataInput file) throws IOException, ClassFormatException {
int constant_pool_count = file.readUnsignedShort();
constant_pool = new Constant[constant_pool_count];
/* constant_pool[0] is unused by the compiler and may be used freely
* by the implementation.
*/
for (int i = 1; i < constant_pool_count; i++) {
constant_pool[i] = Constant.readConstant(file);
/* Quote from the JVM specification:
* "All eight byte constants take up two spots in the constant pool.
* If this is the n'th byte in the constant pool, then the next item
* will be numbered n+2"
*
* Thus we have to increment the index counter.
*/
if (constant_pool[i] != null) {
byte tag = constant_pool[i].getTag();
if ((tag == Constants.CONSTANT_Double) || (tag == Constants.CONSTANT_Long)) {
i++;
}
}
}
}
/**
* Get constant from constant pool.
*
* @param index Index in constant pool
* @return Constant value
* @see Constant
*/
public Constant getConstant( int index ) {
if (index >= constant_pool.length || index < 0) {
throw new ClassFormatException("Invalid constant pool reference: " + index
+ ". Constant pool size is: " + constant_pool.length);
}
return constant_pool[index];
}
/**
* Get constant from constant pool and check whether it has the
* expected type.
*
* @param index Index in constant pool
* @param tag Tag of expected constant, i.e., its type
* @return Constant value
* @see Constant
* @throws ClassFormatException
*/
public Constant getConstant( int index, byte tag ) throws ClassFormatException {
Constant c;
c = getConstant(index);
if (c == null) {
throw new ClassFormatException("Constant pool at index " + index + " is null.");
}
if (c.getTag() != tag) {
throw new ClassFormatException("Expected class `" + Constants.CONSTANT_NAMES[tag]
+ "' at index " + index + " and got " + c);
}
return c;
}
}
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