src/java.base/share/classes/java/util/regex/PatternSyntaxException.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * under the terms of the GNU General Public License version 2 only, as
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 * accompanied this code).
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package java.util.regex;

/**
 * Unchecked exception thrown to indicate a syntax error in a
 * regular-expression pattern.
 *
 * @since 1.4
 */

public class PatternSyntaxException
    extends IllegalArgumentException
{
    @java.io.Serial
    private static final long serialVersionUID = -3864639126226059218L;

    /** @serial */
    private final String desc;
    /** @serial */
    private final String pattern;
    /** @serial */
    private final int index;

    /**
     * Constructs a new instance of this class.
     *
     * @param  desc
     *         A description of the error
     *
     * @param  regex
     *         The erroneous pattern
     *
     * @param  index
     *         The approximate index in the pattern of the error,
     *         or {@code -1} if the index is not known
     */
    public PatternSyntaxException(String desc, String regex, int index) {
        this.desc = desc;
        this.pattern = regex;
        this.index = index;
    }

    /**
     * Retrieves the error index.
     *
     * @return  The approximate index in the pattern of the error,
     *         or {@code -1} if the index is not known
     */
    public int getIndex() {
        return index;
    }

    /**
     * Retrieves the description of the error.
     *
     * @return  The description of the error
     */
    public String getDescription() {
        return desc;
    }

    /**
     * Retrieves the erroneous regular-expression pattern.
     *
     * @return  The erroneous pattern
     */
    public String getPattern() {
        return pattern;
    }

    /**
     * Returns a multi-line string containing the description of the syntax
     * error and its index, the erroneous regular-expression pattern, and a
     * visual indication of the error index within the pattern.
     *
     * @return  The full detail message
     */
    public String getMessage() {
        StringBuilder sb = new StringBuilder();
        sb.append(desc);
        if (index >= 0) {
            sb.append(" near index ");
            sb.append(index);
        }
        sb.append(System.lineSeparator());
        sb.append(pattern);
        if (index >= 0 && pattern != null && index < pattern.length()) {
            sb.append(System.lineSeparator());
            for (int i = 0; i < index; i++) {
                sb.append((pattern.charAt(i) == '\t') ? '\t' : ' ');
            }
            sb.append('^');
        }
        return sb.toString();
    }

}