原因:long 和 Integer 之间没有任何继承关系，都继承于Number类
测试代码：
public class test{
public static void main(String[] args){
long num_long = 2;
Integer num_integer = 3;
//long Integer int 转换
int num1 = 1;
num1 = num_integer;
System.out.println("Integer 转 int : "+ num1);
int num2 = 1;
num2 = (int)num_long;
System.out.println("long 转 int : "+ num2);
num_integer =(Integer)((Long) num_long).intValue();
System.out.println("long 转 Integer : "+ num_integer);
long num_long1 = 2;
Integer num_integer1 = 3;
num_long1 =((long) num_integer1);
System.out.println("Integer 转 long : "+ num_long1);
}
}
输出结果:
Integer 转 int : 3
long 转 int : 2
long 转 Integer : 2
Integer 转 long : 3