了解： 当作字符串连接符

字符串在前，基本数据类型基本上沦陷为拼接

public class Demo2 {
    public static void main(String[] args) {
        int a =3;
        int b = 4;
        String str = "hell0";
        System.out.println(a+b + str);  //7hello
        System.out.println(str+a+b);    //hello34
        System.out.println(str+(a+b));  //hell07
    }