win.doyto.query.core.StringJoiner Maven / Gradle / Ivy

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package win.doyto.query.core;

/**
 * StringJoiner
 *
 * @author f0rb on 2019-06-04
 */
class StringJoiner {
    private final char[] joiner;
    private final String[] list;
    private int count = 0;
    private int cursor = 0;

    public StringJoiner(String joiner, int size) {
        this.joiner = joiner.toCharArray();
        list = new String[size];
    }

    public StringJoiner append(String str) {
        list[cursor++] = str;
        count += str.length();
        // 追加扩容策略
        return this;
    }

    @Override
    public String toString() {
        String[] strings = list;
        int joinerLength = joiner.length;
        int capacity = count + joinerLength * (strings.length - 1);
        char[] chars = new char[capacity];

        String str = strings[0];
        int length = str.length();
        str.getChars(0, length, chars, 0);

        int location = length;

        for (int i = 1; i < cursor; i++) {

            System.arraycopy(joiner, 0, chars, location, joinerLength);
            location += joinerLength;

            str = strings[i];
            length = str.length();
            str.getChars(0, length, chars, location);

            location += length;
        }

        return new String(chars);
    }

}