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Apache Commons Lang, a package of Java utility classes for the classes that are in java.lang's hierarchy, or are considered to be so standard as to justify existence in java.lang. The code is tested using the latest revision of the JDK for supported LTS releases: 8, 11, 17 and 21 currently. See https://github.com/apache/commons-lang/blob/master/.github/workflows/maven.yml Please ensure your build environment is up-to-date and kindly report any build issues.

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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.commons.lang3.text.translate;

import java.io.IOException;
import java.io.Writer;

/**
 * Translates codepoints to their Unicode escaped value.
 *
 * @since 3.0
 * @version $Id: UnicodeEscaper.java 1666535 2015-03-13 18:18:59Z britter $
 */
public class UnicodeEscaper extends CodePointTranslator {

    private final int below;
    private final int above;
    private final boolean between;

    /**
     * Constructs a UnicodeEscaper for all characters. 
     */
    public UnicodeEscaper(){
        this(0, Integer.MAX_VALUE, true);
    }

    /**
     * Constructs a UnicodeEscaper for the specified range. This is
     * the underlying method for the other constructors/builders. The below
     * and above boundaries are inclusive when between is
     * true and exclusive when it is false. 
     *
     * @param below int value representing the lowest codepoint boundary
     * @param above int value representing the highest codepoint boundary
     * @param between whether to escape between the boundaries or outside them
     */
    protected UnicodeEscaper(final int below, final int above, final boolean between) {
        this.below = below;
        this.above = above;
        this.between = between;
    }

    /**
     * Constructs a UnicodeEscaper below the specified value (exclusive). 
     *
     * @param codepoint below which to escape
     * @return the newly created {@code UnicodeEscaper} instance
     */
    public static UnicodeEscaper below(final int codepoint) {
        return outsideOf(codepoint, Integer.MAX_VALUE);
    }

    /**
     * Constructs a UnicodeEscaper above the specified value (exclusive). 
     *
     * @param codepoint above which to escape
     * @return the newly created {@code UnicodeEscaper} instance
     */
    public static UnicodeEscaper above(final int codepoint) {
        return outsideOf(0, codepoint);
    }

    /**
     * Constructs a UnicodeEscaper outside of the specified values (exclusive). 
     *
     * @param codepointLow below which to escape
     * @param codepointHigh above which to escape
     * @return the newly created {@code UnicodeEscaper} instance
     */
    public static UnicodeEscaper outsideOf(final int codepointLow, final int codepointHigh) {
        return new UnicodeEscaper(codepointLow, codepointHigh, false);
    }

    /**
     * Constructs a UnicodeEscaper between the specified values (inclusive). 
     *
     * @param codepointLow above which to escape
     * @param codepointHigh below which to escape
     * @return the newly created {@code UnicodeEscaper} instance
     */
    public static UnicodeEscaper between(final int codepointLow, final int codepointHigh) {
        return new UnicodeEscaper(codepointLow, codepointHigh, true);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean translate(final int codepoint, final Writer out) throws IOException {
        if (between) {
            if (codepoint < below || codepoint > above) {
                return false;
            }
        } else {
            if (codepoint >= below && codepoint <= above) {
                return false;
            }
        }

        // TODO: Handle potential + sign per various Unicode escape implementations
        if (codepoint > 0xffff) {
            out.write(toUtf16Escape(codepoint));
        } else {
          out.write("\\u");
          out.write(HEX_DIGITS[(codepoint >> 12) & 15]);
          out.write(HEX_DIGITS[(codepoint >> 8) & 15]);
          out.write(HEX_DIGITS[(codepoint >> 4) & 15]);
          out.write(HEX_DIGITS[(codepoint) & 15]);
        }
        return true;
    }

    /**
     * Converts the given codepoint to a hex string of the form {@code "\\uXXXX"}
     * 
     * @param codepoint
     *            a Unicode code point
     * @return the hex string for the given codepoint
     *
     * @since 3.2
     */
    protected String toUtf16Escape(final int codepoint) {
        return "\\u" + hex(codepoint);
    }
}