java.lang.ExceptionInInitializerError

package test;

import java.util.Arrays;

public class AA {
    private static int[] a = new int[4];
    private static AA aa = new AA();
    boolean[] flag = new boolean[5];
    private static char[] ad = new char[4];

    private AA() {// 构造方法
        init();
    }

    public static AA getAA() {// 得到单态实例
        return aa;
    }

    public void init() {
        Arrays.fill(ad, ‘d‘);// 此处将会出错
        Arrays.fill(a, 1);// 此处不会出错
        Arrays.fill(flag, true);// 此处也不会出错，用作对比
        System.out.println(a[0]);
    }

    /** * @param args */
    public static void main(String[] args) {
        new AA();
    }
}