只要运算中有字符串就会自动转为字符串运算，但是只是从字符串以后的开始字符串链接，前面的不受影响

public class Java {
     public static void main(String[] args) {
          int a = 1;
          int b = 2 ;
          String c = "3";
          System.out.println(a + b + c);        // 33
          System.out.println(c + a + b);        // 123
     }

}