Java中易出现错误的运算符

Java中易出现错误的运算符

1.除：/

把握原则（小转大）

//除运算
int num1 = 12;
int num2 = 5;
int result = num1 / num2;       //取整
System.out.println(result);     //2

double result1 = num1 / num2;   //    num1 / num2为int，再赋给double
System.out.println(result1);    //2.0


double result2 = num1 / num2 + 0.0;     //2.0
double result3 = num1 / (num2 + 0.0);   //2.4
double result4 = (double)num1 / num2;   //2.4
double result5 = (double) (num1 / num2);    //2.0

2.取余:%

//%：取模运算
int a = 12;
int b = 5;
System.out.println("a % b = " + a % b);     //2

int a1 = -12;
int b1 = 5;
System.out.println("a1 % b1 = " + a1 % b1);     //-2

int a2 = 12;
int b2 = -5;
System.out.println("a2 % b2 = " + a2 % b2);     //2

int a3 = -12;
int b3 = -5;
System.out.println("a3 % b3 = " + a3 % b3);     //-2

结论：结果的符号与被模数的符号相同

• 在开发中，经常使用%来判断能否被除尽的情况。

3.自增++、自减--

1. 前++：先自增1，后运算。

2. 后++：先运算，后自增1

   //前++和后++ 、前--和后--
   int x = 10;
   int y = ++x;
   System.out.println("x = " + x + ",y = " + y);   //x=11,y=11
   
   int x1 = 10;
   int y1 = x1++;
   System.out.println("x1 = " + x1 + ",y1 = " + y1);   //x1=11,y1=10
   

• 注意：自增1不会改变变量本身的数据类型；

• 根据++的规律得出--的规律

1. 前--：先自减1，后运算
2. 后--：先运算，后自减1

• 单独前++，后++，结果一样

int x2 = 10;
x2++;
System.out.println(x2);     //11

int x3 = 10;
++x3;
System.out.println(x3);     //11