【答案】： i % 2 == 0

public class TEST { // 奇偶数判断：x % 2 == 0public static void main(String[] args) {for (int i = 1; i < 100; i++) {if (i % 2 == 0) // 填空System.out.println(i * i / 2);elseSystem.out.println((i * i - 1) / 2);}}}