Apache BCEL Source Code Files are inside the Apache BCEL source package file like bcel-6.5.0-src.zip. Unzip the source package file and go to the "src/main" sub-directory, you will see source code files.

Here is the list of Java source code files of the Apache BCEL 6.5.0 in \Users\fyicenter\bcel-6.5.0\src:

⏎ org/apache/bcel/classfile/EnclosingMethod.java

/**
 *  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.bcel.classfile;

import java.io.DataInput;
import java.io.DataOutputStream;
import java.io.IOException;

import org.apache.bcel.Const;

/**
 * This attribute exists for local or
 * anonymous classes and ... there can be only one.
 *
 * @since 6.0
 */
public class EnclosingMethod extends Attribute {

    // Pointer to the CONSTANT_Class_info structure representing the
    // innermost class that encloses the declaration of the current class.
    private int classIndex;

    // If the current class is not immediately enclosed by a method or
    // constructor, then the value of the method_index item must be zero.
    // Otherwise, the value of the  method_index item must point to a
    // CONSTANT_NameAndType_info structure representing the name and the
    // type of a method in the class referenced by the class we point
    // to in the class_index.  *It is the compiler responsibility* to
    // ensure that the method identified by this index is the closest
    // lexically enclosing method that includes the local/anonymous class.
    private int methodIndex;

    // Ctors - and code to read an attribute in.
    EnclosingMethod(final int nameIndex, final int len, final DataInput input, final ConstantPool cpool) throws IOException {
        this(nameIndex, len, input.readUnsignedShort(), input.readUnsignedShort(), cpool);
    }

    private EnclosingMethod(final int nameIndex, final int len, final int classIdx,final int methodIdx, final ConstantPool cpool) {
        super(Const.ATTR_ENCLOSING_METHOD, nameIndex, len, cpool);
        classIndex  = classIdx;
        methodIndex = methodIdx;
    }

    @Override
    public void accept(final Visitor v) {
      v.visitEnclosingMethod(this);
    }

    @Override
    public Attribute copy(final ConstantPool constant_pool) {
        return (Attribute) clone();
    }

    // Accessors
    public final int getEnclosingClassIndex() {
        return classIndex;
    }

    public final int getEnclosingMethodIndex() {
        return methodIndex;
    }

    public final void setEnclosingClassIndex(final int idx) {
        classIndex = idx;
    }

    public final void setEnclosingMethodIndex(final int idx) {
        methodIndex = idx;
    }

    public final ConstantClass getEnclosingClass() {
        final ConstantClass c =
            (ConstantClass)super.getConstantPool().getConstant(classIndex,Const.CONSTANT_Class);
        return c;
    }

    public final ConstantNameAndType getEnclosingMethod() {
        if (methodIndex == 0) {
            return null;
        }
        final ConstantNameAndType nat =
            (ConstantNameAndType)super.getConstantPool().getConstant(methodIndex,Const.CONSTANT_NameAndType);
        return nat;
    }

    @Override
    public final void dump(final DataOutputStream file) throws IOException {
        super.dump(file);
        file.writeShort(classIndex);
        file.writeShort(methodIndex);
    }
}

⏎ org/apache/bcel/classfile/EnclosingMethod.java

Or download all of them as a single archive file:

File name: bcel-6.5.0-fyi.zip
File size: 706792 bytes
Release date: 2020-07-03
Download 

⇒ JDK "javap" Command

⇐ Install Apache BCEL 6.5.0 Binary Package

⇑ Apache BCEL (Byte Code Engineering Library)

⇑⇑ Java Bytecode Tools