我在这设计输入显示偶数个图片，为什么我整个程序运行是没反应？

public LLKTableModel(int r, int c) {
        // 创建数组
        st = new String[r][c];// 分配了内存

        // 给数组中每个格子放上图片文件名字
        for (int i = 0; i < r ; i++)
            for (int j = 0; j < c; j++) {
                int f=1;// 下面while函数的判断词
                java.util.Random ran = new java.util.Random();
                int index = ran.nextInt(6);
                st[i][j] = "images/" + index + ".gif";
                int k = (ran.nextInt(r / 2)) + r / 2;
                int h = ran.nextInt(c);
                while (f == 1) {
                    if ("".equals((st[k][h]))) {
                        st[k][h] = st[i][j];break;

                    } else {
                        k = (ran.nextInt(r / 2)) + r / 2;
                        h = ran.nextInt(c);
                        break;

                    }
                }
            }

    }