Apache Ant Source Code Files are inside the Apache Ant source package file like apache-ant-1.10.10-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 Ant 1.10.10 in \Users\fyicenter\apache-ant-1.10.10\src\main:

⏎ org/apache/tools/ant/BuildLogger.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
 *
 *      https://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.tools.ant;

import java.io.PrintStream;

/**
 * Interface used by Ant to log the build output.
 *
 * A build logger is a build listener which has the 'right' to send output to
 * the ant log, which is usually <code>System.out</code> unless redirected by
 * the <code>-logfile</code> option.
 *
 */
public interface BuildLogger extends BuildListener {

    /**
     * Sets the highest level of message this logger should respond to.
     *
     * Only messages with a message level lower than or equal to the
     * given level should be written to the log.
     * <P>
     * Constants for the message levels are in the
     * {@link Project Project} class. The order of the levels, from least
     * to most verbose, is <code>MSG_ERR</code>, <code>MSG_WARN</code>,
     * <code>MSG_INFO</code>, <code>MSG_VERBOSE</code>,
     * <code>MSG_DEBUG</code>.
     *
     * @param level the logging level for the logger.
     */
    void setMessageOutputLevel(int level);

    /**
     * Sets the output stream to which this logger is to send its output.
     *
     * @param output The output stream for the logger.
     *               Must not be <code>null</code>.
     */
    void setOutputPrintStream(PrintStream output);

    /**
     * Sets this logger to produce emacs (and other editor) friendly output.
     *
     * @param emacsMode <code>true</code> if output is to be unadorned so that
     *                  emacs and other editors can parse files names, etc.
     */
    void setEmacsMode(boolean emacsMode);

    /**
     * Sets the output stream to which this logger is to send error messages.
     *
     * @param err The error stream for the logger.
     *            Must not be <code>null</code>.
     */
    void setErrorPrintStream(PrintStream err);
}

⏎ org/apache/tools/ant/BuildLogger.java

Or download all of them as a single archive file:

File name: apache-ant-1.10.10-fyi.zip
File size: 2392938 bytes
Release date: 2021-04-17
Download 

⇒ ant-1.8.0.jar - Apache Ant

⇐ Download Apache Ant Source Package

⇑ Apache Ant - Java Build Tool

⇑⇑ Java/JAR Tools