數據結構 串匹配 好難懂

package string;

public class StringTest {

    /**
     * 字符串模式匹配
     */
    public static void main(String[] args) {
        String str = "acabaabaabcacdaabc";
        String p = "abaabcacd";
        KMP kmp = new KMP(str, p);
        int[] next = kmp.nextArr();
        for (int i : next) {
            System.out.print(i + " ");
        }
        System.out.println();
        int index = kmp.match();
        if (index < 0)
            System.out.println("this is no matches!");
        else {
            for (int i = 0, len = p.length(); i < len; i++) {
                System.out.print(str.charAt(i + index));
            }
        }
    }

}

class KMP {
    private String s;
    private String t;

    public KMP(String s, String t) {
        this.s = s;
        this.t = t;
    }

    public int[] nextArr() {
        int k = -1, j = 0;
        int[] next = new int[this.t.length()];
        next[0] = k;
        while (j < this.t.length() - 1) {
            if (k == -1 || this.t.charAt(k) == this.t.charAt(j)) {
                k++;
                j++;
                next[j] = k;
            } else {
                k = next[k];
            }
        }
        return next;
    }

    public int match() {
        int i = 0;
        int j = 0;
        int[] next = nextArr();
        while ((i < this.s.length()) && (j < this.t.length())) {
            if (j == -1 || this.s.charAt(i) == this.t.charAt(j)) {
                i++;
                j++;
            } else {
                j = next[j];
            }
        }
        if (j > this.t.length() - 1)
            return i - this.t.length();
        else
            return -1;
    }
}