a++

public class Demon12 {
    public static void main(String[] args) {
        int a = 3;
        int b = a++;
        System.out.println(a);
        int c =++a;
        System.out.println(a);
        System.out.println(b);
        System.out.println(c);
    }
}
输出：

4
5
3
5

Process finished with exit code 0

public class Demon12 {
    public static void main(String[] args) {
        //++ -- 自增 自减 属于一元运算符
        int a = 3;
        int b = a++;//先赋值b=3,再增加1.
        //a=a+1
        System.out.println(a);
        //a=a+1
        int c =++a;//执行该代码前先加1，再给c赋值。
        System.out.println(a);
        System.out.println(b);
        System.out.println(c);
        System.out.println("===============");

        //用以求3的2次方。
        double pow = Math.pow(3,2);
        System.out.println(pow);
    }
}

输出：

4
5
3
5
===============
9.0

Process finished with exit code 0