a++和++a区别

public class test {
    public static void main(String[] args) {
        int a = 20;
        int b = 30;
        int c = a++;  //先赋值再相加，c=20  a = 21
        System.out.println(c); //20
        System.out.println(a); //21
        int d = ++b; //先自增，再赋值
        System.out.println(d==b);
    }
}