src/java.base/share/classes/sun/text/ComposedCharIter.java

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package sun.text;

import jdk.internal.icu.impl.NormalizerImpl;
import jdk.internal.icu.text.NormalizerBase;

public final class ComposedCharIter {
    /**
     * Constant that indicates the iteration has completed.
     * {@link #next} returns this value when there are no more composed characters
     * over which to iterate.
     */
    public static final int DONE = NormalizerBase.DONE;

    //cache the decomps mapping, so the seconde composedcharIter does
    //not need to get the data again.
    private static int chars[];
    private static String decomps[];
    private static int decompNum;

    static {
        int maxNum = 2100;
        chars = new int[maxNum];
        decomps = new String[maxNum];
        decompNum = NormalizerImpl.getDecompose(chars, decomps);
    }

    /**
     * Construct a new {@code ComposedCharIter}.  The iterator will return
     * all Unicode characters with canonical decompositions, excluding Korean
     * Hangul characters.
     */
    public ComposedCharIter() { }

    /**
     * Returns the next precomposed Unicode character.
     * Repeated calls to {@code next} return all of the precomposed characters defined
     * by Unicode, in ascending order.  After all precomposed characters have
     * been returned, {@link #hasNext} will return {@code false} and further calls
     * to {@code next} will return {@link #DONE}.
     */
    public int next() {
        if (curChar == decompNum - 1) {
            return DONE;
        }
        return chars[++curChar];
    }

    /**
     * Returns the Unicode decomposition of the current character.
     * This method returns the decomposition of the precomposed character most
     * recently returned by {@link #next}.  The resulting decomposition is
     * affected by the settings of the options passed to the constructor.
     */
    public String decomposition() {
        return decomps[curChar];
    }
    private int curChar = -1;
}